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Original research article, building climate resilience in rainfed landscapes needs more than good will.

• 1 Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden
• 2 Consultative Group for International Agricultural Research, Research Program ‘Water, Land and Ecosystems', Colombo, Sri Lanka
• 3 Independent Consultant, Malmö, Sweden
• 4 Independent Consultant, Colombo, Sri Lanka
• 5 International Water Management Institute (IWMI), US Office, Washington, DC, United States
• 6 International Water Management Institute (IWMI), West Africa Office, Accra, Ghana

Rainfed smallholder farming is particularly vulnerable to climate change, which can greatly exacerbate existing poverty and livelihood challenges. Understanding the complexity of the systems that connect the environment, society and people can help us to reduce this vulnerability and increase the resilience of communities and households to climate perturbations. In recent years, resilience theory has proven a useful approach for exploring the complexity of development challenges. As a result, there has been an increase in the development of tools and frameworks for assessing resilience. Despite this increased focus, there is no consistent use of the resilience concept in development practice and little evidence as to the benefits of using the tools. This paper aims to bridge theory and practice by coupling research on resilience with its application in the international development field. The specific hypothesis we explore is if and how rural livelihoods build resilience toward increased climatic variability in already degraded agro-ecological landscapes? We present a resilience framework with indicators to assess the extent of community resilience to climate change through improved local agricultural production and natural resources management. Primary and secondary landscape and community data, together with development of participatory watershed action plans were used to populate 16 indicators in a resilience framework baseline for the two rainfed dominated watersheds in Ethiopia and Ghana respectively. Given community awareness of the challenges related to the watershed natural resources, local agriculture and extreme weather, the communities were very willing to develop action plans to improve their management of natural resources and build climate resilience. Nevertheless, our analysis of the watershed action plans revealed that strengthening resilience through local action alone, would likely not be sufficient to meet all climate -livelihood challenges identified. To address severity and recurrence of climate change related disturbances, such as droughts, floods and disease in poverty-affected rural communities, the capacity to improve resilience will depend on external factors, in addition to inherent action. New knowledge, infrastructure and social security mechanisms, including insurance and emergency assistance need to added to build resilience for poverty-affected communities in degraded watersheds. We conclude there are also challenges in the use of resilience framework for development and climate-action related to rural poverty affected and degraded livelihood systems. Populating complex social–environmental systems will also need further development, to understand progress in resilience building under changing climate. Special attention to systemic indicators that describe the coupling and interdependencies of social-ecosystem factors will be critical to take action.

Introduction

Climate change, rainfall variability and water insecurity with recurrent incidence of droughts and dryspells affecting food security is estimated to affect 3.2 billion people, of which 1.4 billion is living in rural settings ( FAO, 2020 ). Latest report by IPCC (2021) re affirms that incidence and duration of precipitation and other weather related extreme events is already affecting multiple regions, with both more heavy precipitation and more incidence of agricultural and ecological droughts. In sub-Saharan Africa, smallholder farming is a main source of income and livelihood and an intervention area for poverty alleviation and development. Poverty persists, especially in rural areas, where livelihoods are closely related to agricultural production ( Katsushi et al., 2018 ). These areas are already affected by land degradation and soil nutrient depletion ( Leakey et al., 2009 ; Barrett and Bevis, 2015 ), making it a challenge to increase yields at a pace commensurate with population growth. Land degradation affects the well-being of over 3.2 billion people in the world, with the greatest impacts felt by the most vulnerable groups ( IPBES, 2018 ). Furthermore, a high probability of drought and dry spells ( Hyman et al., 2008 ; Rockström and Falkenmark, 2015 ; Gautier et al., 2016 ) make farming systems on degraded land particularly vulnerable to pressure from variable climates. Together these slow and fast social and environmental changes have severe impacts on rural smallholder farming systems, contributing to persistent poverty (e.g. Barrett and Bevis, 2015 ; Enfors, 2015 ; Grace et al., 2017 ). One action to support development is to use participatory pathways for better managing agricultural production systems and local natural resources. The approach are considered key to anticipating and adapting to challenges of weather and climate degraded land and productivity and livelihood impacts, to increase the resilience of rural agricultural communities.

Resilience is a useful concept for capturing the complexity and interactions of social-ecological systems ( Folke et al., 2010 ; Cote and Nightingale, 2012 ). While definitions vary, for the purposes of this study, resilience is defined as “the ability of a system and its component parts to anticipate, absorb, accommodate, or escape from unacceptable standards of living due to the effects of a hazardous event, in a timely and efficient manner ( Douxchamps et al., 2017 ).” In other words, resilience describes the capacity of communities in a given context or landscape to maintain and improve their livelihoods—despite stressors and shocks—through the sustainable management of natural resources while maintaining key ecological functions.

The concept of resilience is increasingly being embedded in development policy at global, regional and national levels ( Brown, 2015 ). For example, resilience to climate change is a fundamental element of several United Nations Sustainable Development Goals, including the goals on poverty reduction, food security, infrastructure, urbanization, climate change and oceans ( UNGA, 2015 ). The Paris Agreement emphasizes climate resilience and the resilience of socio-economic and ecological systems ( UNFCCC, 2015 ) and the Sendai Framework for Disaster Risk Reduction 2015–2030 calls for increased resilience to disasters ( UNISDR, 2015 ). At regional and national levels, resilience is a key focus of policies that address climate change impacts, for example, through commitments to creating climate-resilient communities and economies in the framework of Agenda 2063, The Africa We Want ( African Union, 2015 ), or to increasing agricultural production, in the framework of the African Union's Malabo Declaration on accelerated agricultural growth and transformation for shared prosperity and improved livelihoods ( African Union, 2014 ).

In academic literature, writing on resilience dates back at least to the 1970's (e.g., Holling, 1973 ; Berkes and Folke, 1998 ; Carpenter et al., 2001 ). Efforts to link resilience theory to development have increased in recent years as a means to strengthen capacities to cope with climate-related challenges and to contribute to poverty reduction. Berbés-Blázquez et al. (2017 ) identify multiple overlaps between development resilience strategies, specifically noting the need to adopt a complex systems perspective. To address the different interpretations of resilience across disciplines, Xu and Kajikawa (2017) developed an integrated framework aimed at a generalizing the concept, outlining the principal components irrespective of disciplinary approach. The authors considered aspects of system flexibility, redundancy, diversity, and connectedness. They paid special attention to external and internal slow and fast systems components, to enhance resilience for desired systems outcomes.

The use of resilience to address climate challenges has prompted advances in the development of practical tools for applying resilience theory. Although there are many approaches to measuring resilience in development practice ( UNDP, 2013 ; Béné et al., 2014 ; FAO, 2015 ; Quinlan et al., 2015 ; Douxchamps et al., 2017 ; Sellberg et al., 2017 ), there is little evidence of what can be achieved when different tools are applied. Key challenges concern what to measure and how, to gauge progress and change. Based on a review of more than fifty resilience tools and methodologies, Douxchamps et al. (2017) found that further studies are needed to ensure that resilience theory is fully grounded in empirical observation, and that more attention is paid to the systemic dimensions of social-ecological systems (SES) for accelerated development subject to changes, such as development and climate change.

This paper aims to bridge theory and practice by coupling research on resilience with its application in the international development field. The specific hypothesis we explore is: can rural livelihoods build resilience toward increased climatic variability in already degraded agro-ecological landscapes? To explore this, we present results from the implementation of community-developed watershed action plans aimed at supporting community efforts to improve watershed management for building resilience to climate-related stressors and shocks. We develop baseline data for measuring progress of community resilience related to the agro-ecological landscape and to the dominant livelihoods. And finally we analyse the proposed community plans of action, with specific interest to the systemic indicators, that are key to capture the interconnectedness between the components of the social-ecological system. The protocol was piloted in four watersheds dominated by smallholder farming systems in rainfed agriculture: two in Ghana and two in Ethiopia during 2016 and 2017.

Methodology

Protocol for assessing resilience in rural communities.

The protocol applied in this paper follows the resilience assessment components of developed by Douxchamps et al. (2017) based on the Common Analytical Model for Resilience Measurement ( Constas et al., 2014 ). It involves a mix of methods for data collection and analysis, which take into account multiple perspectives and governance levels. The specific approach in data collection is outlined in Table 1 and in Supplementary Section . In summary, three main approaches were used. Firstly, desk reviews from open access publications and public records were used to the finest spatial resolution and most updated record. For assessing historic watershed landuse change and rainfall data, remote sensing products ( Supplementary Section 2 ). Finally, the community-developed watershed action plans, following the IWMI (2018) “Sustainable Management of Water, Land and Ecosystems for Resilient Communities: Community Workshop Modules” tool were used for qualitative information and analysis of the proposed progress toward climate resilience, in respective location ( Figure 1 ).

Table 1 . List of indicator categories indicators [adopted from Douxchamps et al. (2017) ] and sources of data for measuring the resilience of the agro-ecological systems in G1, G2, E1, and E2 watersheds [adopted from Douxchamps et al. (2017) ].

Figure 1 . Schematic figure outlining data collection related resilience framework components [after Douxchamps et al. (2017) ] in the research study, using a mixed method approach to assess resilience which included landscape assessment using remotes sensing, climate data, desk study of census data and policy review, and the analysis of the community-developed watershed action plans.

The data was then measured against an identified set of indicators (see Table 1 ) derived from Douxchamps et al. (2017) to reveal the baseline level of resilience. The indicators were grouped into three categories: (i) initial states and capacities, which includes indicators on poverty, education, agricultural management, water and sanitation, and livelihoods and strategies to anticipate, absorb, accommodate, or escape stressors and shocks ; (ii) context, including indicators on agro-ecology and climate , i nstitutions and social networks, ecological regulation, functional responses, and connectivity . The systemic factors are particularly important for this indicator category as they have been identified as a gap in many resilience measurement frameworks ( Douxchamps et al., 2017 ). Systemic factors (environmental regulation, self-organization, functional responses, and connectivity) capture the links between systems components, both within the ecological and social systems respectively, as well as between the ecological and social aspects of the watershed. For example, access to inputs, such as irrigation, fertilizers, and pesticides, can result in higher yields, and have a positive impact on household incomes and increase resilience. However, such management practices can also result in the degradation of water surface and groundwater resources, if applied inappropriately, and hence can be considered an indicator for social-ecological system (SES) connectivity indicator. The final indicator category is iii) disturbance, which includes indicators on type, frequency, intensity and effects of shocks and stressors . For the purposes of this study, shocks and stressors were measured at community and district levels based on primary and secondary sources, to provide both objective and subjective understanding of the timing, length and effects of events over the past 25 years. This category also includes the recognition of undesirable stable states.

The indicators are listed in Table 1 and in Supplementary Section 1 section for full description and in Supplementary Section 2 with references to primary and secondary data sources for indicators.

Case Studies in Ethiopia and Ghana

Ethiopia, despite sustained economic growth, remains one of the world's least developed places, ranking 173 out of 186 countries in the 2020 Human Development Index ( UNDP, 2020 ). Weather related extremes are frequent, both as droughts and floods, that affect the largely agriculturally dominated livelihoods and economy. In Ghana, despite increasing growth at the national level and in the south of the country, there are still regions where poverty remains high and infrastructure is poorly developed ( Ghana Statistical Service, 2015 ). In these regions, addressing climate change and other development challenges is vital to reducing poverty and to responding to the vulnerability of rainfed farming systems to climate and temperature variations. The national policy environments in Ghana and Ethiopia provide space for actions to increase resilience to climate change. In Ghana, a review of policies on climate change, environmental resources management and agricultural production found that resilience has featured in policy and strategy documents since 2012 ( IWMI, 2018a , b ). For example, the MESTI (2013) includes resilience among its objectives for agriculture, infrastructure, water land systems and vulnerable communities ( MESTI, 2013 ) and the Ghana Shared Growth and Development Agenda (GSGDA) II (2014–2017) promotes crop varieties that are resilient to climate change ( Giordano and Cofie, 2017 ). In Ethiopia, strengthening resilience is an explicit policy commitment at the national level ( Barron and Debevec, 2016 ). The Federal Democratic Republic of Ethiopia (2011) ; FDRE (2012) identifies the sectors that are most vulnerable to climate change and calls for the development of adaptation plans targeting agriculture, health, water and energy, and the building and transport sectors ( Federal Democratic Republic of Ethiopia, 2011 ). There is also a Desta et al. (2005) aimed at strengthening resilience to climate-related shocks through proposed measures to increase incomes ( Federal Democratic Republic of Ethiopia, 2005 ).

The community developed watershed action plan process was applied in four agricultural watersheds in the Southern Nations, Nationalities and Peoples' Region (SNNP) and Tigray regions in Ethiopia; and in the Upper East and the Northern regions in Ghana. The locations were selected based on the current livelihood systems being dominated by rainfed agriculture, with marginal options for alternative income sources whilst being subject to current or future water resource limitations in landscapes. The four watersheds ( Table 2 ) will be referred to as E1, E2, G1, and G2. In Ethiopia, one of the selected sites had links to ongoing rural development projects (E1), while the second one—selected for comparative purposes—did not (E2).

Table 2 . Characteristics of the selected watersheds ( Oguntunde et al., 2006 ; Ghana Statistical Service, 2015 ; Mul et al., 2015 ; Adimassu, 2016 ; Kadyampakeni et al., 2017 ).

Between 70–80% of the population in G1 and G2 live in rural areas ( Ghana Statistical Service, 2015 ). In Ethiopia, 90% of all rural households rely primarily on agricultural activities. In the watersheds, communities depended almost completely on rainfed farming. Longterm average annual rainfall ranges from 749 mm y −1 in E1 to 1,300 mm y −1 in E2 ( Adimassu, 2016 ), and 1,000 mm y −1 for G1 and G2, respectively ( Kadyampakeni et al., 2017 ).

The community developed watershed action plan (section Protocol for Assessing Resilience in Rural Communities) was piloted in the two watersheds E1 and E2 in Ethiopia in May-June 2016. It was further refined and contextualized with a second trial in the two watersheds in G1 and G2, Ghana in June-July 2017. Facilitated dialogues in local language were organized in the four watersheds to develop the local action plans to build resilience. Results were shared back to communities, 6 months after respective workshop. All participants at all events were informed and consented to the information generated during workshops to be used for research purposes, following IRB standards. The facilitated dialogues to develop local for resilience building action plans followed the protocol described by IWMI (2018) . The workshop was divided into modules corresponding to the Table 1 indicators, where participants were guided through the modules and jointly developed consensus on current state and proposed action plans to build climate resilience in respective watershed. These action plans were analyzed by the research team, and used as primary data to inform on the state and capacity of social-ecological resilience of the four communities in the watersheds. The dialogues included communities from down-, mid, and upstream locations in each watershed, and 20–40 participants per workshop included elderly, young, male and female community members, local government agencies, and representatives from NGOs and watershed experts working with the respective communities. Secondary data was derived from official sources on census, climate and rainfall, land use change, and through policy analyses to triangulate and /or quantitate qualitative statements developed during the workshops by participants.

Scoring System for Resilience Indicators

We applied a 3- grade scoring system to all indicators of the resilience framework, populated with data according to Table 1 and Supplementary Sections 2, 3 . The 3-grade indicator scale provide a course indicator to guide the baseline of resilience of the agro-ecological systems in E1, E2, G1, and G2 watersheds [indicators adopted from Douxchamps et al. (2017) ]. The level of resilience was interpreted through the indicators in order to compare different contexts and understand whether and how resilience changes ( Hills et al., 2015 ). The groups of indicators were scored as to the effect on the community's resilience to climate change, where (+) indicates that the state of the measured indicator is positive; (0) indicates no effect, and (−) indicates a negative effect. The indicators for resilience framework categories “contextual factors and systemic indicators” and “Disturbances” are detailed in Table 3 . For full list of indicators, see Supplementary Section 1 .

Table 3 . Extract indicator category “Contextual and systemic indicators” and “Disturbances” and relative scoring.

Each indicator category was then weighted to provide a relative value per category per overall watershed, in terms of resilience for climate disturbances, taking into account the livelihood and community network.

Initial States and Capacities

Initial state and assets of livelihood systems.

When assessing indicators describing initial state of the four watershed and communities, we found Ethiopian sites E1 and E2 being in a relatively less developed state, with higher incidence of poverty, smaller farm sizes, lesser degree of literacy and less developed drinking water and sanitation facilities ( Table 4 ). The major difference was the level of access to improved sanitation, with 10–15% of households lacked improved sanitation in G2 and G1, and 94% lacked improved sanitation in E1 and E2. Access to improved water sources also differ widely, with nearly 80% access in G2 and just above 40% in E2. Notably, all four watershed community consultation reported practices of soil and water conservation (SWC) management to enhance rainfall infiltration and reduce rainfall runoff and sediment losses from crop fields. However, the lack of developed water storage could have negative implications for broader water insecurity and climate resilience in the rainfed-dominated agriculture systems of E1 and E2.

Table 4 . Indicator scoring on assets and use of assets for the four watersheds G1, G2, E1 and E2 [data derived from primary and secondary sources from: WFP (2012 , 2014) , Ghana Statistical Service (2013) , Debevec et al. (2016a , b ), IWMI (2016b) , Amoah and Appoh (2017a , b ), Central Statistical Agency (2017) ].

Capacity to Cope With Stressors and Shocks

The capacity to deal with risk and/or stress is an important indicator of resilience building. When consulted in the development of action plans, there were an inherent challenge of seasonal migratory labor out of communities, especially younger male, but also female. Internal remittances therefore played a role in all four watersheds. The communities in all four watersheds relied on a mix of agricultural activities for their livelihoods, ranging from beekeeping, livestock, shea butter production, aquaculture, and crop production. This diversity was often adding important albeit small incomes.

The results of analyzing the community developed watershed action plans showed that there was a willingness to improve natural resources management. Communities identified and proposed a range of actions to cope with various climate and natural resources-related challenges, in order to improve livelihoods and natural resources in the watershed ( Table 5 ). Proposed action included both behavioral change for community or individuals, such as dietary change, awareness raising and regulatory efforts, and pro-active measures to adapt, and re-inforce natural habitats and ecosystems functions (i.e., tree planting, more SWC practices). Most of the proposed actions were actions already undertaken or well-known in the community, as actions undertaken in the past, to address watershed degradation (i.e., SWC, tree planting) or when disturbances occurred (i.e., migrate, change diet when crops fail, sell livestock). Most communities explicitly recognized the importance of capacity building and awareness raising as an important component to build an action plan for resilience in the watershed. Only one location (G2) explicitly mentioned alternative coping strategies to diversify income generation through e.g., sale of livestock, or through migration for seeking alternative labor opportunities.

Table 5 . Summary of proposed natural resource management actions to build resilience in respective watershed (E1,E2, G1,G2).

Contextual Factors and Systemic Factors

Contextual factors included indicators on climate and ecosystems, social and systemic factors and the change of these factors ( Tables 6 , 7 ). In this protocol, focus was in particular on rainfall patterns and landuse changes of the four cases studies. Overall, only weak signals of rainfall change could be identified, with potential serious implication for the rainfed agricultural production systems. In G1 and G2, the incidence of dry spells of more than 7 days was likely to occur in more than 80% of seasons, with potential implication of yield reductions ( Kadyampakeni et al., 2017 ). In E1 and E2, rainfall analyses over the last 20 years showed a re-distribution of rainfall with decrease in annual wet days, as well as a decrease in heavy rainfall ( Gummadi et al., 2018 ). In E1 there short rains (Belg) had significantly reduced and were no longer considered for crop production ( Supplementary Section 3 ) Unexpectedly, the landuse change analyses showed that the permanent vegetation (tree cover) had increased in E1 and E2, and remained largely unchanged between 1987 and 2017 in G1 and G2, but spatially redistributed ( Supplementary Section 3 ).

Table 6 . Indicator scoring results on contextual factors for the four watersheds G1, G2, E1, E2.

Table 7 . Indicator scoring results on contextual systemic factors for the four watersheds G1, G2, E1 and E2.

Regarding social factors “institutions” and “social networks,” consultations with local communities in development of action plans showed that there are formal and informal social networks in place in the event of a crisis for most of the communities in the four watersheds. In response to drought, support included receiving seedlings and awareness efforts around bush burning from the Ministry of Forestry and Agriculture (G1); technical expertise for improved farming practices from agriculture extension officers (G2); and food aid from the government (all watersheds).

A range of institutions were identified for various roles in managing natural resources in the different watersheds. The communities in G2, E1, and E2 identified themselves as having a key role, but this was limited to labor rather than decision-making. All of the communities relied mainly on their district assemblies to address issues around natural resources management. Public service agricultural extension officers were identified as having great influence on farming activity through information sharing and training. Local and international NGOs also provided such services as well as funding.

The systemic factors (environmental regulation, self-organization, functional responses, and connectivity) capture the links between systems components, both within the ecological and social systems respectively, as well as between the ecological and social aspects of a community and the watershed ( Table 7 ). Land degradation was perceived as high across all four watersheds, and in G1 and G2, changes in water quality were linked to activities such as farming and keeping livestock. Communities only connected downstream water resource issues (water quality, water quantity) with community use upstream in the action plan development. We interpreted this as there was marginal awareness of the respective communities and the use of natural resources actual and potential effects in the watersheds (G1, G2, and E2). This unawareness of connectivity between use and emerging effects suggested a limited capacity to address challenges related to the dynamics, such as upstream-downstream water pollution. Other natural resources that may be implicated were the use of communal land (E1, E2), and abstraction of surface water upstream.

Disturbance

Stability and shocks.

The data on stability and shocks focus on events with both slow and fast incidence of change, including drought, floods, storms, erosion and landslides, fires, pest and disease outbreaks, market (price structure) collapse and political conflicts, as mentioned by the communities in the action plan development process. Figure 2 shows the type and frequency of events over a 25-year period that the participants recalled as a community in respective watershed. The events present the perspective of the communities, although not always possible to triangulate with independent verification, such as rainfall analyses. The data suggest that stressors and shocks were multiple and frequently recurring, which exacerbated the impacts of natural climatic variability on communities and watersheds. Most locations experienced either too little or too much rainfall every 3–5 years. E2 was particularly exposed to frequent floods, droughts and erosion events, -a significant challenge since these types of events require different responses. G2, on the other hand, only experienced a few events and listed none after year 2000. Interestingly, all of the watersheds listed fewer shocks during the period 2005–2015 than before 2000. It is unclear if this an indication of improved coping strategies, or a reflection of methodological weakness (i.e., workshop participant age distribution, and/or with impaired memories).

Figure 2 . Frequency and type of shocks and disturbances during the past 25 years (1990–2015) as recalled by the communities in the four watersheds during the consultative development of watershed action plans. Data drawn from Oguntunde et al. (2006) , Debevec et al. (2016a , b ), IWMI (2016b) , and Amoah and Appoh (2017a , b ).

Summary of Resilience Indicator Status

To compare the four case watershed baseline of resilience, the 16 indicators were average into the resilience framework indicator categories “Initial state and capacities,” “Contextual and systemic factors,” and “Disturbances” ( Figure 1 ). Figure 3 summarizes the results from the three categories of indicators as presented in Tables 4 – 7 and Figure 2 . The results indicate the relative level of resilience in the different watersheds, specifying weaker and stronger components in each watershed.

Figure 3 . Summary result for baseline resilience based on resilience framework indicator categories for four cases E1, E2 G1, G2. (−) decreases the resilience of the system; (0) does not impact the resilience of the system, negatively or positively; (+) positively impacts the resilience of the system.

The G2 watershed stands out, since its average score was highest across the indicator categories. The ability of G2 to anticipate, absorb, accommodate the impacts of shocks and stressors exceeded that in the other watersheds, as indicated in the proposed actions in the community action plans. A key factor could be the community's proximity to a large city, which provides access to health, education, markets and information, which exceeds any other watershed.

In terms of disturbances, here related primarily to drought and flood events, E1, E2, and G1 are already having a historic and current high exposure to extreme weather events. Due to the contextual and systemic category also scoring negative, we interpret this as an inherent weak capacity to build resilience, and therefore also two concurring set of indicator categories further act to set back this capacity.

E2 consistently scored slightly lower than the other watersheds. Poverty levels were higher and access to water and sanitation services were lower. Despite greater rainfall levels, land degradation was a challenge and there was an increasing trend in dry extreme events. A key aspect was also low connectivity and access to key infrastructure, which is important for external support in the event of disturbances.

Capacity to Increase Resilience in Ghana and Ethiopia Case Studies

We explored the capacity to build resilience in four rural communities of smallholder rainfed dominated agriculture, highly dependent on past and current weather and local natural resource base in watersheds. Data for a baseline in resilience was established, using a mixed method approach combining primary evidence through a consultation process and secondary complementary data on climate, landuse, and statistical livelihood context from multiple sources. We acknowledge it does not reflect individual perspectives on well-being, or differences in well-being among different groups and individuals. Nevertheless, the data enables a baseline understanding of the communities' potential to respond to climatic events or other external or internal stressors and disturbances, such as extreme weather events expected to be on the increase (e.g., IPCC, 2021 ). The capacity to respond to shocks and stressors varied between the communities. While all of the communities were eager to reduce the impact of climate change and current landscape degradation through watershed management with additional natural resources management efforts, the proposed action plans were unlikely to be sufficient to address slow variables or severe shocks, such as prolonged or more recurring drought events, severe floods, or soil fertility decline. In a recent study, Findlater et al. (2018) confirmed that even well-resourced farmers struggle to adopt climate change management approaches, despite incentive and willingness to adapt.

Drought is a particular challenge. Historically, the response to severe droughts included external food aid from government agencies and NGOs. The community response to such events included migration (E1, E2), selling livestock (G2), or change of diet (E2)—actions that can help temporarily (e.g., seasonal dry periods), but which can lead to decreased resilience in the long term. Labor migration tends to age the rural populations, and undermine willingness to invest in longterm interventions. Change in climate parameters have been shown to negatively affect child early year development (e.g., Randell et al., 2020 ) and the most likely pathways were proposed to be change in diets due to limited food supply by agriculture. Furthermore, recurring severe shocks can act as a disincentive to investment in agriculture ( Hansen et al., 2019 ) and thus undermine necessary climate adaptation.

Other measures that can support resilience but were not mentioned by the communities, include strengthening market access, (micro) loan facilities, savings or insurance mechanisms. In a review of climate risk interventions, Hansen et al. (2019) found that institutional interventions, such as insurance and social-protection programs, alongside improved farming practices, can increase the ability of smallholders to cope in the event of a severe shock, including climate and extreme-weather related shocks. Notably, whereas all action plans included elements on information access, awareness making and capacity (knowledge) strengthening, these are generally not possible to address within communities themselves. Identifying solutions to new and complex challenges, such as livelihood- environmental development, sustainability and climate adaptation, tend to require innovation and knowledge often sourced externally, merged with local knowledge.

The systemic factors revealed that the communities had practices that could increase resilience by increasing yields, such as the use of organic and inorganic fertilizers, or keeping livestock, which increase livelihood benefits, but can simultaneously result in water quality changes. Other practices such as SWC practices often proposed to reduce climate change impacts are already in place. Hence, it is doubtful if “more of the same” will strengthen resilience further, especially as the main variable of rainfall is increasing in variability or even declining in seasonal amounts ( Table 6 ). Chemura et al. (2020) suggest that current rainfed crops of maize, sorghum, cassava and groundnut in Ghana, is already cultivated under suboptimal agro-ecological conditions, and these will be increased by >12% under expected climate change. Appropriate and diversified agricultural management practices can support stable production and have a positive impact on resilience ( Hansen et al., 2019 ). However, management practices can also result in the degradation of natural resources if, for example, they lead to water pollution into surface and groundwater sources, unsustainable water withdrawals or soil degradation. These aspects need to be managed at an integrated landscape—watershed scale to balance opportunity with potential negative impacts within other resource users or downstream area of practice.

Challenges in Application of the Protocol in Ghana and Ethiopia

This paper provides a snapshot of the current state of resilience in the four watersheds. Understanding the relative change in resilience over time will require tracking changes over time. The timing of the measurements, taking into account seasonality, will be important for enabling comparisons ( Barrett and Constas, 2014 ). Data gathering and verification is a continuous problem, which calls for mixed methods approaches including participatory consultation, to ensure the precision of resilience measuring. A careful selection of indicators will allow a more detailed analysis, but add cost and analyses to be executed. We used a pragmatic 3-level scale relative scale for indicators to compare the four livelihood- watershed cases identified in Ethiopia and Ghana for the similarities in terms of rainfed agricultural dependencies and a perceived degree of land—oil degradation. We acknowledge the oversimplification to describe complex social—ecological systems with quantitative and qualitative data with such relative scale. Yet, the selection of key indicators indicator categories based on the resilience framework, with a consistent approach in data collection across cases, provided results to compare and rank the four cases into more or less resilient baseline state. And further, this protocol provided guidance on which category or even specific indicator, may be critical to action to build social—ecological resilience in respective watershed to build climate resileince.

Systemic indicators do not receive much attention in existing resilience measurement and assessment frameworks ( Douxchamps et al., 2017 ) despite their importance ( Xu and Kajikawa, 2017 ). This study advance the discussion on systemic indicators, the metrics and the ways to enhance them for building resilience and balance development and sustainability under added challenge of climate change. A number of questions remain. For example, does measuring systemic factors add to the understanding of resilience in a system, or are there other ways to approach the question? The indicators used for measuring the systemic factors in this study largely overlapped with other indicators and, to a great extent, focused on either social or ecological aspects of the system ( Table 1 ). Constas et al. (2014) observed that measuring resilience should involve a systems perspective, with measures that are sensitive to interconnected sets of relationships. Grafton et al. (2019) emphasized a pragmatic approach to guide context specific progress to resilience for environmentally focused SES. However, by explicitly consider systemic indicators, the systems lens is applied throughout the measurement process.

A transformation to more resilient and improved livelihoods is the aim of most development projects and should be explicit in resilience measurement frameworks. This analysis shows that external inputs, regarding technical assistance, new knowledge, and (public service) support, such as social support as well as coordinated and adaptive management of emerging environmental impacts, will be needed to support a transformation. The need for these support actions will only increase, as climate change offset greater challenges for smallholder rural farming systems dependent on variable rainfall, and already affected by degraded landscapes.

The key finding of the study is that the capacity of communities to improve their resilience may not be adequate to deal with emerging climate change, despite a high level of willingness to improve their natural resources management to better cope with stressors and shocks. The community action plans developed through facilitated dialogues were largely informed by agricultural “best practices,” including water and soil-land conservation practices and revegetation efforts at household-individual scale. The proposed action plans lacked innovation, nor did they always adequately respond to the challenges of climatic change and extreme weather. Furthermore, the plans did not include poverty alleviation efforts such as strengthening market access, loan facilities or safety nets. To achieve greater resilience, these communities will thus have to depend on external factors and actors, to progress under current development challenges, and further under added burden of increased temperatures and rainfall variability. Differences among communities will also impact their opportunities and abilities to increase resilience and find pathways out of poverty.

The concept of resilience can help capture the complexity of well-being challenges by addressing social and ecological interconnectedness, and the slow and fast drivers that shape SES systems. A better balance is needed to ensure that application of resilience frameworks and resilience measurement is anchored in research as well as in practical actions. For example, in selecting indicators and including key aspects of resilience, such as systemic factors and transformation, data availability will continue to pose a challenge for context-specific analyses. This requires collaboration by practitioners in development and academic expertise, to accelerate evidenced-based development under increasing challenges such as climate change.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Author Contributions

JB conceptualized full case study, developed protocol for manuscript, and participatory case studies, includes background documentation supported by MG. SS led desk synthesis of four case studies and conceptualize indicator framework. ZA undertook climatic and landuse change studies and supported participatory processes in Ethiopia and Ghana. All authors contributed to manuscript development and writing.

This work was supported by the United States Agency for International Development (USAID) CGIAR-natural resource management (NRM) Public International Organization (PIO) grant no. EEM-G−00-04-00010 to the International Water Management Institute (IWMI), with additional support from the CGIAR Research Program on Water, Land and Ecosystems (WLE). The opinions expressed here are the sole responsibility of the authors.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Acknowledgments

The manuscript benefitted from two diligent editors help. We thank the partners and communities who participated in this effort.

Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fclim.2021.735880/full#supplementary-material

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Keywords: social-ecological system, agriculture, watershed development, dryland, Ghana, Ethiopia, community participation, resilience

Citation: Barron J, Skyllerstedt S, Giordano M and Adimassu Z (2021) Building Climate Resilience in Rainfed Landscapes Needs More Than Good Will. Front. Clim. 3:735880. doi: 10.3389/fclim.2021.735880

Received: 03 July 2021; Accepted: 11 November 2021; Published: 16 December 2021.

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Copyright © 2021 Barron, Skyllerstedt, Giordano and Adimassu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Jennie Barron, jennie.barron@slu.se

This article is part of the Research Topic

Climate Risk Management in Smallholder Agriculture

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Adapting agriculture to climate change via sustainable irrigation: biophysical potentials and feedbacks

Lorenzo Rosa 1

Published 10 June 2022 • © 2022 The Author(s). Published by IOP Publishing Ltd Environmental Research Letters , Volume 17 , Number 6 Focus on the Future of Water-Limited Agricultural Landscapes Citation Lorenzo Rosa 2022 Environ. Res. Lett. 17 063008 DOI 10.1088/1748-9326/ac7408

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1 Department of Global Ecology, Carnegie Institution for Science, Stanford, CA, United States of America

Lorenzo Rosa https://orcid.org/0000-0002-1280-9945

• Received 17 March 2022
• Accepted 27 May 2022
• Published 10 June 2022

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Irrigated agriculture accounts for ∼90% of anthropogenic freshwater consumption, is deployed on 22% of cultivated land, and provides 40% of global food production. Expanding irrigation onto currently underperforming rainfed croplands is crucial to meet future global food demand without further agricultural expansion and associated encroachment of natural ecosystems. Establishing irrigation is also a potential climate adaptation solution to alleviate heat- and water-stress to crops and reduce climate variability and extremes. Despite irrigation being one of the land management practices with the largest environmental and hydroclimatic impacts, the role of irrigation to adapt agriculture to climate change and achieve global sustainability goals has just started to be quantified. This study reviews biophysical opportunities and feedbacks of 'sustainable irrigation'. I describe the concept of sustainable irrigation expansion—where there are opportunities to increase agricultural productivity over currently water-limited rainfed croplands by adopting irrigation practices that do not deplete freshwater stocks and impair aquatic ecosystems. Expanding sustainable irrigation may avert agricultural expansion but create additional externalities that are often neglected. This review highlights major gaps in the analysis and understanding on the role of sustainable irrigation expansion to adapt agriculture to climate change. This study reviews the implications of a potential sustainable irrigation expansion on (a) global food security, (b) hydroclimatic conditions, (c) water quality, (d) soil salinization, (e) water storage infrastructure, and (f) energy use. These implications help to explain the challenges of achieving sustainability in irrigated agriculture and thus also point toward solutions and future research needs.

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1. Introduction

Feeding the growing and increasingly affluent human population requires doubling global food production by 2050 [ 1 ] as well as reducing food waste and shifting diets [ 2 – 8 ]. Advances in agricultural practices have reduced hunger around the world, but at the same time have contributed significantly to climate change, biodiversity loss, and degradation of land and water resources [ 9 – 11 ]. Thus, ensuring sufficient and equitable access to food while reducing agriculture's environmental impacts is one of the greatest societal challenges of the 21st century.

Box 1. Concepts and definitions about sustainable irrigation.

Water withdrawals: The volume of water abstracted from a water body. Depending on its use, withdrawn water is partly consumed and partly returned to a water body where it is available for future use.

Water consumption: The volume of water used and not returned to water bodies after its withdrawals. Consumed water becomes unavailable for future use by human activities in the same watershed.

Irrigated agriculture: Agricultural practices that artificially apply water to croplands through tubes, pumps, and sprays. Irrigation allows crops to grow under non-water limiting conditions.

Rainfed agriculture: Agricultural practices that solely depend on precipitation and no irrigation water is provided to crops. The productivity of rainfed agriculture highly depends on climatic conditions and is particularly vulnerable to vagaries in temperature and precipitation patterns which are intensifying due to global warming [ 45 ]. Importantly, I here define rainfed agriculture as crop production without irrigation independently on the climate. However, rainfed and dryland agriculture can be distinguished by humid and semiarid climates, respectively [ 52 ].

Dryland agriculture: Agricultural practices without irrigation and less than 500 mm yr −1 of precipitation [ 52 ].

Sustainable irrigation: Irrigation practices are defined as sustainable when their water consumption does not exceed local renewable water availability, does not impair environmental flows, and does not deplete freshwater stocks [ 53 ]. Here, sustainable irrigation indicates sustainability from the water quantity point of view and does not indicate sustainability of the agricultural system in broader terms, namely nutrient use, water quality, soil, energy use, or biodiversity.

Environmental flows: Freshwater flows with appropriate quantity, timing, and quality to sustain freshwater ecosystems and their processes as well as direct human benefits [ 54 ].

Sustainable irrigation expansion: Opportunities to increase crop yields from currently water-limited rainfed croplands by adopting sustainable irrigation practices that do not deplete freshwater stocks and impair aquatic ecosystems [ 21 ].

Expanding irrigation onto currently underperforming rainfed croplands is crucial to meet future global food demand without further expansion of croplands and associated encroachment of natural ecosystems [ 21 – 23 , 27 , 28 ]. Global warming has and will increasingly reduce agricultural productivity and affect global food security [ 29 – 37 ]. Rainfed agriculture is highly dependent on climatic conditions and sustains 60% of global food production. Thus, rural communities that rely the most on rainfed agriculture will be most impacted by climate change [ 38 – 41 ]. As global warming aggravates water- and heat-stress events over rainfed croplands [ 42 – 44 ], establishing irrigation as a potential climate adaptation solution can alleviate heat- and water-stress to crops and reduce climate variability and extremes [ 23 , 45 ].

Irrigated areas more than doubled in the past 60 years and currently account for 22% of global croplands [ 46 ]. While most of the irrigation expansion in the 20th century happened during the Green Revolution [ 47 ], global irrigated areas still expanded by an additional 52 million hectares between year 2000 and 2019, reaching a total of 341 million hectares. Population growth will be a key driver for future irrigation expansion and according to recent projections, global irrigated agriculture could double by 2050 reaching up to 800 million hectares [ 48 ] and thus increasing water demand for irrigation [ 49 – 51 ]. However, there are biophysical limits to water and land availability especially with climate change.

This study explores biophysical opportunities and feedbacks of sustainable irrigation. This review describes the concept of 'sustainable irrigation', where water consumption does not exceed local renewable water available in surface and ground water, and hence does not impair freshwater ecosystems (box 1 ). This study shows the global biophysical extent to which sustainable irrigation can contribute to agricultural intensification without impairing freshwater resources and environmental flows. Expanding sustainable irrigation might avert agricultural expansion but might create additional externalities that are often neglected. This study discusses the implications of a prospective sustainable irrigation expansion on (a) global food security, (b) hydroclimatic conditions, (c) water quality, (d) soil salinization, (e) water storage infrastructure, and (f) energy use. These implications help to explain the challenges of achieving sustainability in irrigated agriculture and thus also point toward solutions and future research needs.

This study aims to fulfill an urgent need as decision makers and institutions are exploring avenues towards global food security in a warmer climate. Thus, this review aims to set the research agenda on the role of irrigation to adapt agriculture to climate change and highlight the externalities of irrigation expansion. Scientist and decision makers should acknowledge the role of irrigated agriculture to adapt agriculture to climate change to avoid underestimating potential environmental and climatic implications.

1.1. Irrigation methods and irrigation efficiency

There are different sources of irrigation water, irrigation methods and efficiencies. Water for irrigation can be sourced from groundwater or from surface water through rivers, lakes, reservoirs, or other sources such as treated wastewater or desalinated brackish or salt water [ 55 – 57 ]. Depending on how irrigation water is distributed to crops, there are different irrigation systems, including surface, sprinkler, and drip [ 58 ]. Surface irrigation consists in applying water over cultivated lands by gravity and includes furrow, basin, and border irrigation systems. Sprinkler irrigation applies water to crops in a controlled manner like rainfall while drip irrigation applies water directly to the crops. Not all irrigation systems are suitable for every crop type. The suitability of irrigation systems for croplands also depends on other factors including but not limited to energy requirements, maintenance, labor intensity, capital and operation costs [ 58 ]. Irrigation systems also have different irrigation efficiencies—the volume of irrigation water optimally used by crops during photosynthesis divided by the total water diverted or applied to the cropland [ 59 ]. With 85%–95%, drip irrigation has the highest irrigation efficiency, followed by sprinkler (65%–85%), and surface irrigation (40%–70%) [ 58 , 60 ]. While highly efficient irrigation systems can reduce irrigation water consumption, higher water consumption efficiency rarely reduces overall water consumption creating a rebound effect, where irrigators switch to more water intensive crops or expand irrigated area [ 60 ].

1.2. The unsustainability of irrigation

Irrigated agriculture has higher yields than rainfed agriculture and is crucial for food security because it sustains 40% of global food production although only 22% of cultivated areas are irrigated (table 1 ). However, half of irrigation water consumption is currently unsustainable, i.e. their water consumption exceeds local renewable water availability and therefore deplete environmental flows and freshwater stocks [ 53 ]. Unsustainable irrigation practices include abstraction of pre-historic water from groundwater [ 61 ], pumping of groundwater at a rate that mine an aquifer [ 62 ], or rivers flow depletion with deleterious effects on aquatic species and ecosystems [ 25 , 63 , 64 ]. Unsustainable irrigation has substantially degraded local and downstream water flows in various regions of the world, including the US High Plains, California's Central Valley, the North China Plain and the Indo-Gangetic Basin [ 21 , 25 , 65 – 68 ] (figure 1 ). Thus, the extensive reliance of food production on unsustainable irrigation threatens global and local water and food security.

Figure 1.  The global extent of sustainable irrigation over cultivated lands. (A) Sustainable and unsustainable irrigation over currently irrigated croplands, and potential for sustainable irrigation expansion onto rainfed croplands under 3 °C warmer climate. (B) Country-specific additional irrigated lands with sustainable irrigation expansion potential under 3 °C warmer climate. Figure (A) shows the sustainability of irrigation at 10 km resolution and determines regions that are suitable for the intensification of agriculture through sustainable irrigation. A 3 °C warmer climate with respect to the pre-industrial era represent the plausible level of global warming expected to be reached by the end of the century under current policies [ 75 , 76 ]. Data source [ 23 ].

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Table 1.  Global statistics on irrigation.

Croplands with unsustainable irrigation grow crops that feed 1.3 billion people [ 53 ]. Yet, a significant portion of food thus produced does not contribute to local food security but is part of the international food trade [ 69 – 72 ]. Globally, 15% of unsustainable irrigation volumes are used to produce agricultural commodities for the export market [ 53 ]. China and European nations are major importers of these agricultural commodities while India, Pakistan, the United States and Mexico are their major exporters [ 53 , 70 , 73 ]. Most remunerative crops such as cotton, sugar cane, vegetables and fruits are responsible for two thirds of global unsustainable irrigation water consumption devoted to grow crops for exports [ 53 ]. Therefore, there are important trade-offs to consider between the economic benefits and the environmental impacts of unsustainable irrigation practices [ 74 ].

1.3. Agricultural economic water scarcity

Understanding where existing land, water, and technology are available for sustainable intensification of agriculture is central to developing viable policies for achieving global sustainability targets. On some croplands with available water resources in lakes, streams, or groundwater reservoirs, irrigation is not in place because of socio-economic and institutional barriers—a phenomenon defined as 'agricultural economic water scarcity' [ 22 ]. In fact, socioeconomic aspects play a major role for the development of irrigation [ 77 , 78 ]. Over croplands facing agricultural economic water scarcity, accessing available water resources would allow the expansion of sustainable irrigation and achieve food security goals.

With present-day precipitation and ambient temperature patterns, there is enough locally available water to expand irrigation sustainably over 35% of agricultural lands around the globe, thus boosting food production to feed 1.4 billion additional people without depleting water resources or encroaching natural areas [ 23 ]. Sustainable irrigation can be implemented by using locally available water resources that do not impair freshwater ecosystems and deplete rivers, lakes, reservoirs, and groundwater. These results highlight the potential of overcoming economic water scarcity and enhancing productivity in countries with modest socioeconomic development especially across sub-Saharan Africa, Eastern Europe, and Central Asia.

1.4. Irrigation expansion potential under global warming

Agricultural interventions adopted under current climate conditions may be ineffective under future global warming. By the end of the century, freshwater limitations could require the reversal of 60 million hectares from irrigated to rainfed [ 79 ]. However, climate change is altering rainfall patterns [ 80 ] in a way that will exacerbate water-stress over 70 million hectares of currently rainfed croplands, which provide food for 700 million people worldwide [ 23 ]. From a thermodynamic perspective, climate change is also expected to increase extreme heat waves, which can reduce crop yields directly through heat-stress and indirectly by raising atmospheric vapor pressure deficit and therefore crop water-stress [ 81 – 85 ]. However, from a meteorological perspective, warming might decrease evaporation due to more longwave radiation to the atmosphere, which reduces available energy and evaporation [ 86 ]. Therefore, a warmer climate can create feedbacks that inhibit the expected increase in water use by crops [ 86 ]. Importantly, elevated atmospheric CO 2 could alter water-use efficiency of crops and influence crop productivity [ 35 , 87 – 89 ].

Rainfed croplands are particularly sensitive to increased climate variability and extremes. Establishing sustainable irrigation onto water-stressed rainfed croplands is a prominent adaptation and mitigation measure that can provide a reliable supply of water to water-stressed crops and alleviate heat-stress and contribute to more reliable and resilient crop production [ 23 , 90 – 94 ]. Reducing irrigation water demand, improving water productivity, and increasing soil moisture are all climate adaptation solutions to implement sustainable irrigation in an increasingly water scarce world.

Even with a 3 °C warmer climate with respect to the pre-industrial era—the plausible level of global warming expected to be reached by the end of the century under current policies [ 75 , 76 ]—an expansion of irrigation is sustainably feasible in Latin America, Eastern Europe, and sub-Saharan Africa (figure 1 (A)). The United States, Russia, Brazil, and Nigeria will be the countries with the largest cropland extent for sustainable irrigation expansion (figure 1 (B)). Figure 1 identifies the rainfed cropping systems and countries where irrigation water requirements can be sustainably met either through short-term water storage using rainwater-harvesting schemes or with longer-term water storage in larger reservoirs [ 23 ]. However, extreme weather associated with climate change will increase intra-annual variability in water resources, requiring the construction of reservoirs to store excess water for irrigation (figure 2 ). Even though large tracts of contemporary rainfed croplands will not be suitable for irrigation expansion with a 3 °C warmer climate, large reservoirs could be constructed to store enough water to maintain global sustainable irrigation expansion potential under climate change (figure 2 ). Globally, in a 3 °C warmer climate, long-term water storage in large reservoirs could help to feed 1.2 billion more people than water storage with rainwater-harvesting techniques, which only store water for few days or weeks (figure 2 ). As climate change reduces rainfall in farming regions, investments in water storage infrastructure will grow more important for food security.

Figure 2.  The global potential for sustainable irrigation expansion under current and 3 °C warmer climate conditions. Additional irrigated lands (left), sustainable water consumption (center), and people (right) that could be fed by applying different water storage strategies, namely short-term water storage using rainwater-harvesting schemes and long-term water storage in large reservoirs. A 3 °C warmer climate with respect to the pre-industrial era represent the plausible level of global warming expected to be reached by the end of the century under current policies [ 75 , 76 ]. Data source [ 23 ].

1.5. Opportunities for implementing sustainable irrigation under climate change

There are two approaches to implement sustainable irrigation under global warming. The first consists of nature-based solutions to reduce crop water-stress and increase soil moisture by alleviating evaporation and enhancing infiltration [ 95 , 96 ]. Contour stone bund, pitting, and terracing are farming techniques that increase soil moisture by reducing surface runoff and enhancing infiltration [ 97 ]. Agroforestry, mulching and no-till farming can improve water retention in soils and reduce evaporation by decreasing exposure to sunlight due to shading [ 98 ]. Removing weeds can further reduce nonproductive evaporation and increase water availability to crops [ 96 ]. The alternative approach consists in engineered solutions that aim to reduce water demand and increase water availability. Water demand can be reduced by planting less water-intensive crops and improving crop water productivity [ 99 – 101 ], shifting to more efficient sprinkler and drip irrigation systems [ 96 ], and implementing deficit irrigation practices where crops are grown under mild water-stress conditions with minimal effects on yields [ 22 ]. Irrigation water demand can be reduced by installing photovoltaic panels over croplands to mitigate evaporation due to shading [ 102 ]. A strategy to increase water available to crops is the adoption of rainwater harvesting techniques to capture and store rainwater for supplemental irrigation [ 96 , 103 , 104 ]. Solar powered drip irrigation systems are a sustainable irrigation solution promoted by the United Nations [ 105 ].

2. Implications of sustainable irrigation expansion

Intensification of agriculture with sustainable irrigation expansion might avert agricultural expansion into pristine ecosystems but might create additional externalities. An expansion of irrigation over several million hectares will affect global food security, hydroclimatic conditions, water quality, soil salinization, water storage infrastructure, and energy use (figure 3 ). Following, I discuss the implications of sustainable irrigation expansion. These implications help to explain the challenges of achieving sustainability in irrigated agriculture and thus also point toward solutions and future research needed.

Figure 3.  Socio-environmental and hydroclimatic implications of sustainable irrigation expansion.

2.1. Global food security

Current irrigation practices produce calories that can feed 3.4 billion people worldwide (figure 4 ). As unsustainable irrigation currently produce food that feed 1.3 billion people (figure 4 ), the extensive reliance on unsustainable irrigation in the face of climate change and diminishing freshwater resources threatens global and local food security [ 106 , 107 ]. Changes in climate might imply that current unsustainable irrigation practices may no longer be an option. For example, without irrigation, the current irrigated regions in the western United States, China, and India may need to transition to rainfed agriculture because of freshwater limitations, leading to a loss of calorie production that can feed 490 million people [ 79 ].

Figure 4.  Global food security potential of sustainable irrigation. The figure shows the number of people fed with current sustainable and unsustainable practices and the potential number of people that could be fed with sustainable irrigation expansion in a 3 °C warmer climate using different water storage strategies, namely short-term water storage using rainwater-harvesting schemes and long-term water storage in large reservoirs. Data source [ 22 , 23 ].

The food production lost with elimination of unsustainable irrigation practices could be offset by expanding irrigation over rainfed croplands affected by agricultural economic water scarcity (figure 4 ). Even under global warming, the global food security potential of sustainable irrigation expansion would be maintained with substantial investments in water storage infrastructure. In a 3 °C warmer climate, sustainable irrigation expansion could feed an additional 0.2 billion people either through short-term water storage using rainwater-harvesting techniques and 1.2 billion people with longer-term water storage in larger reservoirs (figure 4 ). These results show that targeted policy and farming decisions could achieve important reductions in unsustainable irrigation demand without compromising global food security.

Figure 5 shows country-specific additional number of people that could be fed with sustainable irrigation expansion under current and 3 °C warmer climate conditions. Even under the current climate, most countries can feed more people with sustainable irrigation, e.g. 166 million in Russia, 120 million in Nigeria, 82 million in the United States and 69 million in China. With future climate, sustainable irrigation expansion potential in most countries could feed the same number of more people, but will likely be lower for Russia, Ukraine, and Poland (figure 5 ). These results highlight those agricultural interventions adopted under current climate conditions may not yield the same benefits under future global warming.

Figure 5.  Country-specific additional people potentially fed with sustainable irrigation under current and 3 °C warmer climate conditions. Source [ 23 ].

2.2. Hydroclimatic feedback

The expansion of irrigation in the 20th century has affected hydroclimatic conditions in many regions [ 108 – 114 ]. The increase in evaporation induced by irrigation has increased atmospheric moisture altering precipitation and temperature patterns [ 115 , 116 ]. By enhancing evapotranspiration, irrigation affects the surface energy balance and is a driver of land surface cooling [ 117 , 118 ] and change in precipitation patterns [ 119 – 123 ].

The expansion of irrigation in the 20th century has alleviated extreme hot temperatures for approximately 1 billion people and consequently also reduced crops exposure to hot extremes [ 93 ]. However, the cooling caused by irrigation has amplified human exposure to moist heat stress through increased air humidity, especially in arid regions where there is a greater increase in evaporation from irrigation [ 124 , 125 ]. Thus, irrigated agriculture in a warmer climate may intensify lethal heat stress by exposing humans to heat and humidity too severe for human survivability [ 126 – 129 ]. Moist heat might also reduce labor productivity of farmers [ 130 ] and therefore affect agricultural productivity and food security.

Irrigated agriculture has several hydroclimatic trade-offs that should be thoroughly evaluated in future climate projections. Even though future irrigated areas and agricultural water management will alter climatic conditions, the current generation of Earth system models do not account for the various irrigation practices in climate projections. Changes in temperature and rainfall patterns may affect both crop water demand and the availability of water for irrigation, thus modifying the spatial extent of regions of, or the optimal irrigation practice for, sustainable irrigation expansion. It is also unclear whether a sustainable irrigation expansion will alleviate heat-stress to crops in the face of further warming.

2.3. Water storage infrastructure

Meeting future sustainable irrigation expansion potential requires more water storage to bridge temporal mismatches between water availability and crop water demand. In a warmer climate, large water storage infrastructure needs to be constructed to store enough water to maintain current irrigation expansion potentials [ 23 ] (figure 3 ), and its shortage will likely be a continuing driver of agricultural economic water scarcity [ 22 ]. Providing water storage infrastructure adds additional social, economic, and ecologic challenges for future food systems, and remains a major knowledge gap to evaluate the economic and environmental implications of expanding irrigation.

Large dams and reservoirs have been a defining feature of infrastructure building in the 20th century [ 131 ]. In fact, water stored in man-made reservoirs is an important source for irrigation [ 56 ]. A reliance on an 'hard-path' water governance approach with large, centralized, capital-intensive irrigation projects had several impacts on ecosystems, coastal processes, and riparian livelihoods [ 132 – 135 ]. Few large rivers have escaped the 'hydraulic mission' of the 20th century [ 131 ] and only around 23% of the world's rivers flow uninterrupted to the ocean [ 136 ], making them of great interest for global conservation efforts. There are also systemic challenges associated to a hard-path water governance approach. Increasing water storage for irrigation can also fuel 'reservoir effects', vicious cycles in which increasing storage leads to over-proportionate growth in demand and reliance on reservoir storage, fueling unsustainable water use and increasing vulnerability to climatic extremes [ 137 , 138 ]. Water storage demand for irrigation could also drive construction of additional dams and increase competition for water storage between irrigated agriculture and hydropower production [ 139 ]. Regulation of surface water flows through dammed reservoirs for irrigation also increases evapotranspiration rates and influence climatic conditions [ 138 ].

'Soft-path' water harvesting solutions for irrigation are an alternative to hard-path solutions [ 132 ]. Soft-path solutions rely on small, modular, decentralized water management, namely water harvesting with small check dams, managed aquifer recharge by creating artificial streams and pond or local catchment systems, and better water management [ 96 , 103 , 104 , 140 , 141 ]. Managed aquifer recharge harvests floodwater to recharge aquifers and is a promising solution to reduce flood risks and store surplus water for irrigation [ 142 ]. Importantly, by reducing the capital and operational costs of hard-path irrigation systems, soft-path solutions are more likely to benefit smallholder farms facing agricultural economic water scarcity and energy poverty [ 143 ].

Global warming will change future water storage supply and demand for agriculture. Less winter snow and or earlier snow and glacier meltwater patterns will influence the amount and timing of water available for agriculture and will likely increase the need to store water for irrigation [ 144 – 147 ]. Changes in crop water use due to elevated atmospheric CO 2 [ 148 , 149 ], or farmers' adaptation to global warming through changes in cropping systems [ 100 ], harvest frequency [ 150 ], and croplands migration [ 151 – 153 ] will further alter future water storage requirements for agriculture. Additionally, irrigated agriculture and water storage will also likely be important components in climate adaptation and mitigation strategies for carbon neutrality, such as bioenergy with carbon capture and storage [ 154 , 155 ]. In fact, increased demand for bio-energy crops for carbon dioxide removal is projected to drive a further expansion of irrigated croplands [ 156 ], furthering pressures on water resources [ 157 , 158 ].

2.4. Water quality

An intensification of agriculture with irrigation expansion will affect water quality and nutrient loading into water bodies [ 159 , 160 ]. Intensive irrigation, often paired with increased fertilizer and pesticide applications [ 18 ], exacerbates fertilizer and pesticide leaching, which have negative impacts on water quality and further disrupt ecosystem processes [ 161 ]. The leaching of phosphorous and nitrogen fertilizer alters biogeochemical cycles [ 162 , 163 ] and creates algal blooms and anoxic dead zones, which impair aquatic ecosystems and generate serious threats to human health [ 164 , 165 ].

Irrigation practices are also a driver of freshwater salinization [ 166 ]. Evapotranspiration concentrates salts contained in irrigation water on the surface of croplands. These salts are then transported into water bodies during rainfall events increasing freshwater salinity and water scarcity [ 167 , 168 ]. Additional irrigation means less water in freshwater bodies, which in turn means less water available to dilute nutrients, sediment, chemicals and other water quality issues caused by agriculture [ 169 ]. Future irrigation expansion must therefore be considered in designing strategies for managing water quality.

2.5. Soil salinization

Soil salinization is a natural process in arid regions with low rainfall, high evapotranspiration rates and presence of soluble salts in runoff [ 170 ]. It is a land degradation process that decreases soil fertility and is a significant component of desertification processes in the world's drylands [ 171 ]. Another driver of soil salinization in the world's drylands is the evapotranspiration of irrigation water carrying dissolved salts, which leads to salts accumulation in the root zone [ 172 , 173 ]. By limiting plant water uptake and therefore reducing crop productivity [ 174 ], soil salinization is a global threat to food security already affecting 20% of global irrigated areas [ 175 , 176 ]. Expansion of irrigated areas, poor irrigation practices (e.g. insufficient irrigation water application and use of saline or brackish water), combined with higher evapotranspiration rates and change in precipitation patterns under global warming are expected to increase soil salinization [ 170 , 177 ].

2.6. Energy implications

A transition from rainfed to irrigated agriculture also has energy implications [ 178 ]. Most irrigation practices require energy to move water from the abstraction source to the field and are usually powered with fossil fuels-based energy sources, such as diesel-powered irrigation pumps [ 179 ]. In countries with intensive irrigated agriculture, the energy used for irrigation systems is considerable [ 180 , 181 ]. As irrigated areas expand, greenhouse gas emissions from irrigation practices will increase. Therefore, an expansion of irrigation means that predictions of agricultural greenhouse gas emissions might be much lower than they will be since these predictions do not account for likely irrigation expansion. The energy use and greenhouse gas emissions associated with irrigation are poorly understood and have only partially been considered in water management planning.

Irrigation energy use directly relates to the depth and distance from which water is pumped and transported. Thus, irrigation systems might require substantial energy for pumping and delivering water to crops [ 182 ]. Irrigation plays a dominant role in direct energy use in farm operations, with an energy intensity of 8 (±6) GJ ha −1 yr −1 [ 181 ]. These broad range of values reflect the differences in irrigation practices, irrigation water requirements, and groundwater pumping [ 181 ]. Importantly, groundwater pumping is the most energy-intensive irrigation practice and groundwater depth is crucial for energy-intensity assessments [ 181 , 183 ]. Additional energy and greenhouse gas emissions from irrigation expansion will come from the production of machineries and infrastructure required to industrialize agriculture from rainfed to irrigated systems [ 178 ]. While a shift to more efficient irrigation technologies can reduce energy and greenhouse gas emissions due to lower pumping of water, declines in water levels and deeper groundwater levels in water scarce regions can offset energy efficiency gains from efficient irrigation technologies [ 184 ]. Solar powered drip irrigation systems are a cost-effective solution promoted by the United Nations to reduce dependence on fossil fuels-based irrigation and reliance on international markets for energy import [ 105 , 185 ].

3. Conclusions

Sustainable irrigation expansion is an important strategy to increase food production and meet future food demand without further expansion of croplands and associated encroachment of natural ecosystems. This study describes the concept of 'sustainable irrigation', where water consumption does not exceed local renewable water available in surface and ground water, and hence does not impair freshwater ecosystems. This study reviews the biophysical potentials and implications of sustainable irrigation expansion under current and future climate conditions. By reducing heat- and water-stress events over croplands, I describe the potential role that irrigated agriculture might have to adapt agriculture to global warming. This study shows that sustainable irrigation can contribute to agricultural intensification and global food security but might create additional externalities that require further investigation.

This review highlights some major gaps in the analysis and understanding on the role of sustainable irrigation expansion in adapting agriculture to climate change. More specifically, (a) more work needs to be done to investigate the food security implications of irrigation expansion. Irrigation expansion may allow for multi-cropping and determine a shift in planting dates and crop types with consequent impacts on food security and nutrition [ 186 ]; (b) the hydroclimate feedback of irrigation and its cooling effect have only recently been acknowledged and more work should be done to include irrigation in climate projections with Earth system models; (c) it is unclear how and where a sustainable irrigation expansion will alleviate heat-stress to crops and how it will affect future agricultural productivity under global warming; (d) irrigation expansion and climate change will require additional water storage to maintain irrigation potential. The socio-economic and environmental feasibility of water storage infrastructure are currently overlooked; (e) irrigation expansion is often paired with other changes in agricultural practices through an industrialization of agriculture and an increase in fertilizer application [ 178 ], which has energy implications and create additional greenhouse gas emissions that are still unquantified; (f) it is also not clear how and where the increased fertilizer applications will likely affect biogeochemical cycles and water quality; (g) while the economic value of irrigation water has been estimated [ 187 , 188 ], the economic feasibility and profitability of irrigation expansion and infrastructure still needs to be evaluated; (h) a sustainable irrigation expansion will also be a driver of soil salinization and freshwater salinization. The drivers and feedbacks of salinization require further investigation.

The vulnerability of food production systems to climate change has been recognized by the United Nations [ 45 ]. Investments in sustainable irrigation expansion may contribute to alleviating poverty (sustainable development goal (SDG) 1), improving food security (SDG 2), ensuring adequate water resources for humans and ecosystems (SDG 6), increasing resilience and adaptive capacity to climate change (SDG 13), and halting biodiversity loss (SDG 15). Understanding where existing land, water, and technology are available for a sustainable intensification of agriculture is central to developing viable policies for achieving these goals. By identifying, at high spatial resolution, the location and productivity potential of croplands affected by agricultural economic water scarcity, it is possible to provide clear and actionable next steps for decisions makers to implement policy mechanisms to ensure global food security.

Acknowledgments

I thank Professor Inez Fung (University of California Berkeley) for valuable comments on this manuscript. Part of the material presented here is part of my PhD dissertation, which can be accessed online [ 189 ].

Data availability statement

No new data were created or analyzed in this study.

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• Published: 28 March 2024

New water accounting reveals why the Colorado River no longer reaches the sea

• Brian D. Richter   ORCID: orcid.org/0000-0001-7216-1397 1 , 2 ,
• Gambhir Lamsal   ORCID: orcid.org/0000-0002-2593-8949 3 ,
• Landon Marston   ORCID: orcid.org/0000-0001-9116-1691 3 ,
• Sameer Dhakal   ORCID: orcid.org/0000-0003-4941-1559 3 ,
• Laljeet Singh Sangha   ORCID: orcid.org/0000-0002-0986-1785 4 ,
• Richard R. Rushforth 4 ,
• Dongyang Wei   ORCID: orcid.org/0000-0003-0384-4340 5 ,
• Benjamin L. Ruddell 4 ,
• Kyle Frankel Davis   ORCID: orcid.org/0000-0003-4504-1407 5 , 6 ,
• Astrid Hernandez-Cruz   ORCID: orcid.org/0000-0003-0776-5105 7 ,
• Samuel Sandoval-Solis 8 &
• John C. Schmidt 9  

Communications Earth & Environment volume  5 , Article number:  134 ( 2024 ) Cite this article

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Persistent overuse of water supplies from the Colorado River during recent decades has substantially depleted large storage reservoirs and triggered mandatory cutbacks in water use. The river holds critical importance to more than 40 million people and more than two million hectares of cropland. Therefore, a full accounting of where the river’s water goes en route to its delta is necessary. Detailed knowledge of how and where the river’s water is used can aid design of strategies and plans for bringing water use into balance with available supplies. Here we apply authoritative primary data sources and modeled crop and riparian/wetland evapotranspiration estimates to compile a water budget based on average consumptive water use during 2000–2019. Overall water consumption includes both direct human uses in the municipal, commercial, industrial, and agricultural sectors, as well as indirect water losses to reservoir evaporation and water consumed through riparian/wetland evapotranspiration. Irrigated agriculture is responsible for 74% of direct human uses and 52% of overall water consumption. Water consumed for agriculture amounts to three times all other direct uses combined. Cattle feed crops including alfalfa and other grass hays account for 46% of all direct water consumption.

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Introduction

Barely a trickle of water is left of the iconic Colorado River of the American Southwest as it approaches its outlet in the Gulf of California in Mexico after watering many cities and farms along its 2330-kilometer course. There were a few years in the 1980s in which enormous snowfall in the Rocky Mountains produced a deluge of spring snowmelt runoff capable of escaping full capture for human uses, but for most of the past 60 years the river’s water has been fully consumed before reaching its delta 1 , 2 . In fact, the river was overconsumed (i.e., total annual water consumption exceeding runoff supplies) in 16 of 21 years during 2000–2020 3 , requiring large withdrawals of water stored in Lake Mead and Lake Powell to accommodate the deficits. An average annual overdraft of 10% during this period 2 caused these reservoirs– the two largest in the US – to drop to three-quarters empty by the end of 2022 4 , triggering urgent policy decisions on where to cut consumption.

Despite the river’s importance to more than 40 million people and more than two million hectares (>5 million acres) of cropland—producing most of the vegetable produce for American and Canadian plates in wintertime and also feeding many additional people worldwide via exports—a full sectoral and crop-specific accounting of where all that water goes en route to its delta has never been attempted, until now. Detailed knowledge of how and where the river’s water is used can aid design of strategies and plans for bringing water use into balance with available supplies.

There are interesting historical reasons to explain why this full water budget accounting has not been accomplished previously, beginning a full century ago when the apportionment of rights to use the river’s water within the United States was inscribed into the Colorado River Compact of 1922 5 . That Compact was ambiguous and confusing in its allocation of water inflowing to the Colorado River from the Gila River basin in New Mexico and Arizona 6 , even though it accounts for 24% of the drainage area of the Colorado River Basin (Fig.  1 ). Because of intense disagreements over the rights to the Gila and other tributaries entering the Colorado River downstream of the Grand Canyon, the Compact negotiators decided to leave the allocation of those waters rights to a later time so that the Compact could proceed 6 . Arizona’s formal rights to the Gila and other Arizona tributaries were finally affirmed in a US Supreme Court decision in 1963 that also specified the volumes of Colorado River water allocated to California, Arizona, and Nevada 7 . Because the rights to the Gila’s waters lie outside of the Compact allocations, the Gila has not been included in formal accounting of the Colorado River Basin water budget to date 8 . Additionally, the Compact did not specify how much water Mexico—at the river’s downstream end—should receive. Mexico’s share of the river was not formalized until 22 years later, in the 1944 international treaty on “Utilization of the Waters of the Colorado and Tijuana Rivers and of the Rio Grande” (1944 Water Treaty) 9 . As a result of these political circumstances, full accounting for direct water consumption at the sectoral level—in which water use is accounted according to categories such as municipal, industrial, commercial, or agricultural uses—has not previously been compiled for the Gila River basin’s water, and sectoral accounting for Mexico was not published until 2023 10 .

The physical boundary of the Colorado River Basin is outlined in black. Hatched areas outside of the basin boundary receive Colorado River water via inter-basin transfers (also known as ‘exports’). The Gila River basin is situated in the far southern portion of the CRB in Arizona, New Mexico, and Mexico. Map courtesy of Center for Colorado River Studies, Utah State University.

The US Bureau of Reclamation (“Reclamation”)—which owns and operates massive water infrastructure in the Colorado River Basin—has served as the primary accountant of Colorado River water. In 2012, the agency produced a “Colorado River Basin Water Supply and Demand Study” 8 that accounted for both the sectoral uses of water within the basin’s physical boundaries within the US as well as river water exported outside of the basin (Fig.  1 ). But Reclamation did not attempt to account for water generated from the Gila River basin because of that sub-basin’s exclusion from the Colorado River Compact, and it did not attempt to explain how water crossing the border into Mexico is used. The agency estimated riparian vegetation evapotranspiration for the lower Colorado River but not the remainder of the extensive river system. Richter et al. 11 published a water budget for the Colorado River that included sectoral and crop-specific water consumption but it too did not include water used in Mexico, nor reservoir evaporation or riparian evapotranspiration, and it did not account for water exported outside of the Colorado River Basin’s physical boundary as illustrated in Fig.  1 . Given that nearly one-fifth (19%) of the river’s water is exported from the basin or used in Mexico, and that the Gila is a major tributary to the Colorado, this incomplete accounting has led to inaccuracies and misinterpretations of “where the Colorado River’s water goes” and has created uncertainty in discussions based on the numbers. This paper provides fuller accounting of the fate of all river water during 2000–2019, including averaged annual consumption in each of the sub-basins including exports, consumption in major sectors of the economy, consumption in the production of specific types of crops, and water consumed by reservoir evaporation and riparian/wetland evapotranspiration.

Rising awareness of water overuse and prolonged drought has driven intensifying dialog among the seven US states sharing the basin’s waters as well as between the United States, Mexico, and 30 tribal nations within the US. Since 2000, six legal agreements affecting the US states and two international agreements with Mexico have had the effect of reducing water use from the Colorado River 7 :

In 2001, the US Secretary of the Interior issued a set of “Interim Surplus Guidelines” to reduce California’s water use by 14% to bring the state within its allocation as determined in the 1963 US Supreme Court case mentioned previously. A subsequent “Quantification Settlement Agreement” executed in 2003 spelled out details about how California was going to achieve the targeted reduction.

In 2007, the US Secretary of the Interior adopted a set of “Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead” that reduced water deliveries to Arizona and Nevada when Lake Mead drops to specified levels, with increasing cutbacks as levels decline.

In 2012, the US and Mexican federal governments signed an addendum to the 1944 Water Treaty known as Minute 319 that reduced deliveries to Mexico as Lake Mead elevations fall.

In 2017, the US and Mexican federal governments established a “Binational Water Scarcity Contingency Plan” as part of Minute 323 that provides for deeper cuts in deliveries to Mexico under specified low reservoir elevations in Lake Mead.i

In 2019, the three Lower Basin states and the US Secretary of the Interior agreed to commitments under the “Lower Basin Drought Contingency Plan” that further reduced water deliveries beyond the levels set in 2007 and added specifications for deeper cuts as Lake Mead drops to levels lower than anticipated in the 2007 Guidelines.

In 2023, the states of California, Arizona and Nevada committed to further reductions in water use through the year 2026 12 .

With each of the above agreements, overall water consumption has been reduced but many scientists assert that these reductions still fall substantially short of balancing consumptive use with 21st century water supplies 2 , 13 . With all of these agreements—excepting the Interim Surplus Guidelines of 2001—set to expire in 2026, management of the Colorado River’s binational water supply is now at a crucial point, emphasizing the need for comprehensive water budget accounting.

Our tabulation of the Colorado River’s full water consumption budget (Table  1 ) provides accounting for all direct human uses of water as either agricultural or MCI (municipal, commercial, industrial), as well as indirect losses of water to reservoir evaporation and evapotranspiration from riparian or wetland vegetation including in the Salton Sea and in a wetland in Mexico (Cienega de Santa Clara) that receives agricultural return flows from irrigated areas in Arizona. We explicitly note that all estimates represent consumptive use , resulting from the subtraction of return flows from total water withdrawals. Table  2 provides a summary based only on direct human uses and does not include indirect consumption of water. We have provided Tables  1 and 2 in English units in our Supplementary Information as Tables SI-1 and SI-2 . We have lumped municipal, commercial, and industrial (MCI) uses together because these sub-categories of consumption are not consistently differentiated within official water delivery data for cities utilizing Colorado River water. More detail on urban water use by cities dependent on the river is available in Richter 14 , among other studies.

We differentiated water consumption geographically using the ‘accounting units’ mapped in Fig.  2 , which are based on the Colorado River Basin map as revised by Schmidt 15 ; importantly, these accounting units align spatially with Reclamation’s accounting systems for the Upper Basin and Lower Basin as described in our Methods, thereby enabling readers accustomed to Reclamation’s water-use reports to easily comprehend our accounting. We have also accounted for all water consumed within the Colorado River Basin boundaries as well as water exported via inter-basin transfers. Water exported outside of the basin includes 47 individual inter-basin transfer systems (i.e., canals, pipelines, pumps) that in aggregate export ~12% of the river’s water. We note that the Imperial Irrigation District of southern California is often counted as a recipient of exported water, but we have followed the rationale of Schmidt 15 by including it as an interior part of the Lower Basin even though it receives its Colorado River water via the All American Canal (Fig.  2 ).

The water budget estimates presented in Tables  1 and 2 are summarized for each of the seven “accounting units” displayed here.

These results confirm previous findings that irrigated agriculture is the dominant consumer of Colorado River water. Irrigated agriculture accounts for 52% of overall consumption (Table  1 ; Figs.  3 and 4 ) and 74% of direct human consumption (Table  2 ) of water from the Colorado River Basin. As highlighted in Richter et al. 11 , cattle-feed crops (alfalfa and other hay) are the dominant water-consuming crops dependent upon irrigation water from the basin (Tables  1 and 2 ; Figs.  3 and 4 ). Those crops account for 32% of all water consumed from the basin, 46% of all direct water consumption, and 62% of all agricultural water consumed (Table  1 ; Fig.  3 ). The percentage of water consumed by irrigated crops is greatest in Mexico, where they account for 86% of all direct human uses (Table  2 ) and 80% of total water consumed (Table  1 ). Cattle-feed crops consume 90% of all water used by irrigated agriculture within the Upper Basin, where the consumed volume associated with these cattle-feed crops amounts to more than three times what is consumed for municipal, commercial, or industrial uses combined.

All estimates based on 2000–2019 averages. Both agriculture and MCI (municipal, commercial, and industrial) uses are herein referred to as “direct human uses.” “Indirect uses” include both reservoir evaporation as well as evapotranspiration by riparian/wetland vegetation.

Water consumed by each sector in the Colorado River Basin and sub-basins (including exports), based on 2000–2019 averages.

Another important finding is that a substantial volume of water (19%) is consumed in supporting the natural environment through riparian and wetland vegetation evapotranspiration along river courses. This analysis—made possible because of recent mapping of riparian vegetation in the Colorado River Basin 16 —is an important addition to the water budget of the Colorado River Basin, given that the only previous accounting for riparian vegetation consumption has limited to the mainstem of the Colorado River below Hoover Dam and does not include vegetation upstream of Hoover Dam nor vegetation along tributary rivers 17 . Given that many of these habitats and associated species have been lost or became imperiled due to river flow depletion 18 —including the river’s vast delta ecosystem in Mexico—an ecologically sustainable approach to water management would need to allow more water to remain in the river system to support riparian and aquatic ecosystems. Additionally, 11% of all water consumed in the Colorado River Basin is lost through evaporation from reservoirs.

It is also important to note a fairly high degree of inter-annual variability in each sector of water use; for example, the range of values portrayed for the four water budget sectors shown in Fig.  5 equates to 24–47% of their 20-year averages. Also notable is a decrease in water consumed in the Lower Basin between the years 2000 and 2019 for both the MCI (−38%) and agricultural sectors (−15%), which can in part be attributed to the policy agreements summarized previously that have mandated water-use reductions.

Inter-annual variability of water consumption within the Lower and Upper Basins, including water exported from these basins. The average (AVG) values shown are used in the water budgets detailed in Tables  1 and 2 .

The water accounting in Richter et al. 11 received a great deal of media attention including a front-page story in the New York Times 19 . These stories focused primarily on our conclusion that more than half (53%) of water consumed in the Colorado River Basin was attributable to cattle-feed crops (alfalfa and other hays) supporting beef and dairy production. However, that tabulation of the river’s water budget had notable shortcomings, as discussed previously. In this more complete accounting that includes Colorado River water exported outside of the basin’s physical boundary as well as indirect water consumption, we find that irrigated agriculture consumes half (52%) of all Colorado River Basin water, and the portion of direct consumption going to cattle-feed crops dropped from 53% as reported in Richter et al. 11 to 46% in this revised analysis.

These differences are explained by the fact that we now account for all exported water and also include indirect losses of water to reservoir evaporation and riparian/wetland evapotranspiration in our revised accounting, as well as improvements in our estimation of crop-water consumption. However, the punch line of our 2020 paper does not change fundamentally. Irrigated agriculture is the dominant consumer of water from the Colorado River, and 62% of agricultural water consumption goes to alfalfa and grass hay production.

Richter et al. 20 found that alfalfa and grass hay were the largest water consumers in 57% of all sub-basins across the western US, and their production is increasing in many western regions. Alfalfa is favored for its ability to tolerate variable climate conditions, especially its ability to persist under greatly reduced irrigation during droughts and its ability to recover production quickly after full irrigation is resumed, acting as a “shock absorber” for agricultural production under unpredictable drought conditions. The plant is also valued for fixing nitrogen in soils, reducing fertilizer costs. Perhaps most importantly, labor costs are comparatively low because alfalfa is mechanically harvested. Alfalfa is increasing in demand and price as a feed crop in the growing dairy industry of the region 21 . Any efforts to reduce water consumed by alfalfa—either through shifting to alternative lower-water crops or through compensated fallowing 20 —will need to compete with these attributes.

This new accounting provides a more comprehensive and complete understanding of how the Colorado River Basin’s water is consumed. During our study period of 2000–2019, an estimated average of 23.7 billion cubic meters (19.3 million acre-feet) of water was consumed each year before reaching its now-dry delta in Mexico. Schmidt et al. 2 have estimated that a reduction in consumptive use in the Upper and Lower Basins of 3–4 billion cubic meters (2.4–3.2 million acre-feet) per year—equivalent to 22–29% of direct use in those basins—will be necessary to stabilize reservoir levels, and an additional reduction of 1–3 billion cubic meters (~811,000–2.4 million acre-feet) per year will likely be needed by 2050 as climate warming continues to reduce runoff in the Colorado River Basin.

We hope that this new accounting will add clarity and a useful informational foundation to the public dialog and political negotiations over Colorado River Basin water allocations and cutbacks that are presently underway 2 . Because a persistent drought and intensifying aridification in the region has placed both people and river ecosystems in danger of water shortages in recent decades, knowledge of where the water goes will be essential in the design of policies for bringing the basin into a sustainable water supply-demand balance.

The data sources and analytical approaches used in this study are summarized below. Unless otherwise noted, all data were assembled for each year from 2000–2019 and then averaged. We acknowledge some inconsistency in the manner in which water consumption is measured or estimated across the various data sources and sectors used in this study, as discussed below, and each of these different approaches entail some degree of inaccuracy or uncertainty. We also note that technical measurement or estimation approaches change over time, and new approaches can yield differing results. For instance, the Upper Colorado River Commission is exploring new approaches for estimating crop evapotranspiration in the Upper Basin 22 . When new estimates become available we will update our water budget accordingly.

MCI and agricultural water consumption

The primary source of data on aggregate MCI (municipal, commercial, and industrial) and agricultural water consumption from the Upper and Lower Basins was the US Bureau of Reclamation. Water consumed from the Upper Basin is published in Reclamation’s five-year reports entitled “Colorado River—Upper Basin Consumptive Uses and Losses.” 23 These annual data have been compiled into a single spreadsheet used for this study 24 . Because measurements of agricultural diversions and return flows in the Upper Basin are not sufficiently complete to allow direct calculation of consumptive use, theoretical and indirect methods are used as described in the Consumptive Uses and Losses reports 25 . Reclamation performs these estimates for Colorado, Wyoming, and Utah, but the State of New Mexico provides its own estimates that are collaboratively reviewed with Reclamation staff. The consumptive use of water in thermoelectric power generation in the Upper Basin is provided to Reclamation by the power companies managing each generation facility. Reclamation derives estimates of consumptive use for municipal and industrial purposes from the US Geological Survey’s reporting series (published every 5 years) titled “Estimated Use of Water in the United States” at an 8-digit watershed scale 26 .

Use of shallow alluvial groundwater is included in the water accounting compiled by Reclamation but use of deeper groundwater sources—such as in Mexico and the Gila River Basin—is explicitly excluded in their accounting, and in ours. Reclamation staff involved with water accounting for the Upper and Lower Basins assume that groundwater use counted in their data reports is sourced from aquifers that are hydraulically connected to rivers and streams in the CRB (James Prairie, US Bureau of Reclamation, personal communication, 2023); because of this high connectivity, much of the groundwater being consumed is likely being sourced from river capture as discussed in Jasechko et al. 27 and Wiele et al. 28 and is soon recharged during higher river flows.

Water consumed from the Lower Basin (excluding water supplied by the Gila River Basin) is published in Reclamation’s annual reports entitled “Colorado River Accounting and Water Use Report: Arizona, California, and Nevada.” 3 These consumptive use data are based on measured deliveries and return flows for each individual water user. These data are either measured by Reclamation or provided to the agency by individual water users, tribes, states, and federal agencies 29 . When not explicitly stated in Reclamation reports, attribution of water volumes to MCI or agricultural uses was based on information obtained from each water user’s website, information provided directly by the water user, or information on export water use provided in Siddik et al. 30 . Water use by entities using less than 1.23 million cubic meters (1000 acre-feet) per year on average was allocated to MCI and agricultural uses according to the overall MCI-agricultural percentages calculated within each sub-basin indicated in Tables  1 and 2 for users of greater than 1.23 million cubic meters/year.

Disaggregation of water consumption by sector was particularly important and challenging for the Central Arizona Project given that this canal accounts for 21% of all direct water consumption in the Lower Basin. Reclamation accounts for the volumes of annual diversions into the Central Arizona Project canal but the structure serves 1071 water delivery subcontracts. We classified every unique Central Arizona Project subcontract delivery between 2000–2019 by its final water use to derive an estimated split between agricultural and MCI uses. Central Arizona Project subcontract delivery data were obtained from the current and archived versions of the project’s website summaries in addition to being directly obtained from the agency through a public information request. Subcontract deliveries were classified based on the final end use, including long-term and temporary leases of project water. This accounting also includes the storage of water in groundwater basins for later MCI or agricultural use. Additionally, water allocated to Native American agricultural uses that was subsequently leased to cities was classified as an MCI use.

Data for the Gila River basin was obtained from two sources. The Arizona Department of Water Resources has published data for surface water use in five “Active Management Areas” (AMAs) located in the Gila River basin: Prescott AMA, Phoenix AMA, Pinal AMA, Tucson AMA, and Santa Cruz AMA 31 . The water-use data for these AMAs is compiled from annual reports submitted by each water user (contractor) and then reviewed by the Arizona Department of Water Resources. The AMA water-use data are categorized by purpose of use, facilitating our separation into MCI and agricultural uses. These data are additionally categorized by water source; only surface water sourced from the Gila River hydrologic system was counted (deep groundwater use was not). The AMA data were supplemented with data for the upper Gila River basin provided by the University of Arizona 32 . We have assumed that all water supplied by the Gila River Basin is fully consumed, as the river is almost always completely dry in its lower reaches (less than 1% flows out of the basin into the Colorado River, on average 33 ).

Data for Mexico were obtained from Hernandez-Cruz et al. 10 based on estimates for 2008–2015. Agricultural demands were estimated from annual reports of irrigated area and water use published by the Ministry of Agriculture and the evapotranspiration estimates of the principal crops published by the National Institute for Forestry, Animal Husbandry, and Agricultural Research of Mexico 10 . The average annual volume of Colorado River water consumption in Mexico estimated by these researchers is within 1% of the cross-border delivery volume estimated by the Bureau of Reclamation for 2000–2019 in its Colorado River Accounting and Water Use Reports 3 .

Exported water consumption

Annual average inter-basin transfer volumes for each of 46 canals and pipelines exporting water outside of the Upper Basin were obtained from Reclamation’s Consumptive Uses and Losses spreadsheet 34 . Data for the Colorado River Aqueduct in the Lower Basin were obtained from Siddik et al. 30 Data for exported water in Mexico was available from Hernandez-Cruz et al. 10 . We assigned any seepage or evaporation losses from inter-basin transfers to their proportional end uses. All uses of exported water are considered to be consumptive uses with respect to the Colorado River, because none of the water exported out of the basin is returned to the Colorado River Basin.

We relied on data from Siddik et al. (2023) to identify whether the water exported out of the Colorado River Basin was for only MCI or agricultural use. When more than one water use purpose was identified, as well as for all major inter-basin transfers, we used government and inter-basin transfer project websites or information obtained directly from the project operator or water manager to determine the volume of water transferred and the end uses. Major recipients of exported water include the Coachella Valley Water District (California); Metropolitan Water District of Southern California (particularly for San Diego County, California); Northern Colorado Water Conservancy District; City of Denver (Colorado); the Central Utah Project; City of Albuquerque (New Mexico); and the Middle Rio Grande Conservancy District (New Mexico). We did not pursue sectoral water-use information for 17 of the 46 Upper Basin inter-basin transfers due to their relatively low volumes of water transferred by each system (<247,000 cubic meters or 2000 acre-feet), and instead assigned the average MCI or agricultural percentage (72% MCI, 28% agricultural) from all other inter-basin transfers in the Upper Basin. The export volume of these 17 inter-basin transfers sums to 9.76 million cubic meters (7910 acre-feet) per year, equivalent to 1% of the total volume exported from the Upper Basin.

Reservoir evaporation

Evaporation estimates for the Upper Basin and Lower Basin are based upon Reclamation’s HydroData repository 35 . Reclamation’s evaporation estimates are based on the standardized Penman-Monteith equation as described in the “Lower Colorado River Annual Summaries of Evapotranspiration and Evaporation” reports 17 . The Penman-Monteith estimates are based on pan evaporation measurements. Evaporation estimates for the Salt River Project reservoirs in the Gila River basin were provided by the Salt River Project in Arizona (Charlie Ester, personal communication, 2023).

Another consideration with reservoirs is the volume of water that seeps into the banks or sediments surrounding the reservoir when reservoir levels are high, but then drains back into the reservoir as water levels decline 36 . This has the effect of either exacerbating reservoir losses (consumptive use) or offsetting evaporation when bank seepage flows back into a reservoir. The flow of water into and out of reservoir banks is non-trivial; during 1999–2008, an estimated 247 million cubic meters (200,000 acre-feet) of water drained from the canyon walls surrounding Lake Powell into the reservoir each year, providing additional water supply 36 . However, the annual rate of alternating gains or losses has not been sufficiently measured at any of the basin’s reservoirs and therefore is not included in Tables  1 and 2 .

Riparian and wetland vegetation evapotranspiration

We exported the total annual evapotranspiration depth at a 30 meter resolution from OpenET 37 using Google Earth Engine from 2016 to 2019 to align with OpenET’s data availability starting in 2016. Total annual precipitation depths, sourced from gridMET 38 , were resampled to align with the evapotranspiration raster resolution. Subsequently, a conservative estimate of the annual water depth utilized by riparian vegetation from the river was derived by subtracting the annual precipitation raster from the evapotranspiration raster for each year. Positive differentials, indicative of river-derived evapotranspiration, were then multiplied by the riparian vegetation area as identified in the CO-RIP 16 dataset to estimate the total annual volumetric water consumption by riparian vegetation across the Upper, Lower, and Gila River Basins. The annual volumetric water consumption calculated over four years were finally averaged to get riparian vegetation evapotranspiration in the three basins. Because the entire flow of the Colorado River is diverted into the Canal Alimentador Central near the international border, very little riparian evapotranspiration occurs along the river south of the international border in the Mexico basin.

In addition to water consumed by riparian evapotranspiration within the Lower Basin, the Salton Sea receives agricultural drain water from both the Imperial Irrigation District and the Coachella Valley Irrigation District, stormwater drainage from the Coachella Valley, and inflows from the New and Alamo Rivers 39 . Combined inflows to the Sea during 2015–2019 were added to our estimates of riparian/wetland evapotranspiration in the Lower Basin.

Similarly, Mexico receives drainage water from the Wellton–Mohawk bypass drain originating in southern Arizona that empties into the Cienega de Santa Clara (a wetland); this drainage water is included as riparian/wetland evapotranspiration in the Mexico basin.

Crop-specific water consumption

The volumes of total agricultural consumption reported for each sub-basin in Tables  1 and 2 were obtained from the same data sources described above for MCI consumption and exported water. The portion (%) of those agricultural consumption volumes going to each individual crop was then allocated according to percentage estimates of each crop’s water consumption in each accounting unit using methods described in Richter et al. 20 and detailed here.

Monthly crop water requirements during 1981–2019 for 13 individual crops, representing 68.8% of total irrigated area in the US in 2019, were estimated using the AquaCrop-OS model (Table SI- 3 ) 40 . For 17 additional crops representing about 25.4% of the total irrigated area, we used a simple crop growth model following Marston et al. 41 as crop parameters needed to run AquaCrop-OS were not available. A list of the crops included in this study is shown in Table SI- 3 . The crop water requirements used in Richter et al. 11 were based on a simplistic crop growth model, often using seasonal crop coefficients whereas we use AquaCrop-OS 40 , a robust crop growth model, to produce more realistic crop growth and crop water estimates for major crops. AquaCrop-OS is an open-source version of the AquaCrop model 42 , a crop growth model capable of simulating herbaceous crops. Additionally, we leverage detailed local data unique to the US, including planting dates and subcounty irrigated crop areas, to produce estimates at a finer spatial resolution than the previous study. We obtained crop-specific planting dates from USDA 43 progress data at the state level. For crops that did not have USDA crop progress data, we used data from FAO 44 and CUP+ model 45 for planting dates. We used climate data (precipitation, minimum and maximum air temperature, reference ET) from gridMET 38 , soil texture data from ISRIC 46 database and crop parameters from AquaCrop-OS to run the model. The modeled crop water requirement was partitioned into blue and green components following the framework from Hoekestra et al. 47 , assuming that blue and green water consumed on a given day is proportional to the amount of green and blue water soil moisture available on that day. When applying a simple crop growth model, daily gridded (2.5 arc minutes) crop-specific evapotranspiration (ETc) was computed by taking the product of reference evapotranspiration (ETo) and crop coefficient (Kc), where ETo was obtained from gridMET. Crop coefficients were calculated using planting dates and crop coefficient curves from FAO and CUP+ model. Kc was set to zero outside of the growing season. We partitioned the daily ETc into blue and green components by following the methods from ref. 41 It is assumed that the crop water demands are met by irrigation whenever it exceeds effective precipitation (the latter calculated using the USDA Soil Conservation Service method (USDA, 1968 48 ). We obtained county level harvested area from USDA 43 and disaggregated to sub-county level using Cropland Data Layer (CDL) 49 and Landsat-based National Irrigation Dataset (LANID) 50 . The CDL is an annual raster layer that provides crop-specific land cover data, while the LANID provides irrigation status information. The CDL and LANID raster were multiplied and aggregated to 2.5 arc minutes to match the AquaCrop-OS output. We produced a gridded crop area map by using this resulting product as weights to disaggregate county level area. CDL is unavailable before 2008. Therefore, we used land use data from ref. 51 in combination with average CDL map and county level harvested area to produce gridded crop harvested area. We computed volumetric water consumption by multiplying the crop water requirement depth by the corresponding crop harvested area.

Data availability

All data compiled and analyzed in this study are publicly available as cited and linked in our Methods section. Our compilation of these data is also available from Hydroshare at: http://www.hydroshare.org/resource/2098ae29ae704d9aacfd08e030690392 .

Code availability

All model code and software used in this study have been accessed from sources cited in our Methods section. We used AquaCrop-OS (v5.0a), an open source version of AquaCrop crop growth model, to run crop simulations. This model is publicly available at http://www.aquacropos.com/ . For estimating riparian evapotranspiration, we used ArcGIS Pro 3.1.3 on the Google Earth Engine. Riparian vegetation distribution maps were sourced from Dryad at https://doi.org/10.5061/dryad.3g55sv8 .

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Acknowledgements

This paper is dedicated to our colleague Jack Schmidt in recognition of his retirement and enormous contributions to the science and management of the Colorado River. The authors thank James Prairie of the US Bureau of Reclamation, Luke Shawcross of the Northern Colorado Water Conservancy District, Charlie Ester of the Salt River Project, and Brian Woodward of the University of California Cooperative Extension for their assistance in accessing data used in this study. The authors also thank Rhett Larson at the Sandra Day O’Connor School of Law at Arizona State University for their review of Arizona water budget data, and the Central Arizona Project for providing delivery data by each subcontract. G.L., L.M., and K.F.D. acknowledge support by the United States Department of Agriculture National Institute of Food and Agriculture grant 2022-67019-37180. L.T.M. acknowledges the support the National Science Foundation grant CBET-2144169 and the Foundation for Food and Agriculture Research Grant No. FF-NIA19-0000000084. R.R.R. acknowledges the support the National Science Foundation grant CBET-2115169.

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B.D.R. designed the study, compiled and analyzed data, wrote the manuscript and supervised co-author contributions. G.L. compiled all crop data, estimated crop evapotranspiration, and prepared figures. S.D. compiled all riparian vegetation data and estimated riparian evapotranspiration. L.S.S. and R.R.R. accessed, compiled, and analyzed data from the Central Arizona Project. D.W. compiled data and prepared figures. A.H.-C. and S.S.-S. compiled and analyzed data for Mexico. J.C.S. compiled and analyzed reservoir evaporation data and edited the manuscript. L.M., B.L.R., and K.F.D. supervised data compilation and analysis and edited the manuscript.

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Richter, B.D., Lamsal, G., Marston, L. et al. New water accounting reveals why the Colorado River no longer reaches the sea. Commun Earth Environ 5 , 134 (2024). https://doi.org/10.1038/s43247-024-01291-0

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A review on harvesting rainwater for agricultural production in the rain-fed region, Ethiopia: challenges and benefits

• Original Article
• Published: 05 November 2023
• Volume 9 , article number  176 , ( 2023 )

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• Dawit Yohannes Meskele   ORCID: orcid.org/0000-0001-6726-9395 1 ,
• Muse Wldmchel Shomore 1 &
• Kero Arigaw Adi 2  

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Due to climate change and increasing population growth, there is high food insecurity in Ethiopia, which results in agricultural economic crises. This crisis can be reduced by increasing agricultural production in a whole part of the country. However, rainfall in arid and semi-arid areas is generally insufficient to meet the basic needs of crop production. In order to improve the livelihoods of its rural communities, the government of Ethiopia has currently started implementing rainwater harvesting (RWH) techniques at the household level. This method can help boost the country’s agricultural production and livestock. The main goal of this review is to examine the status of the knowledge and practices of RWH technology for crop production in Ethiopia. The different reviews conducted in Ethiopia revealed the importance of RWH technologies for the country’s rain-fed regions. The positive effects of macro-catchment systems on water productivity in regions such as Amhara, Oromia, Tigray, and the Southern were among the most important findings. Most of these systems are built and operated in these regions, which gave a good picture of their practices. Besides this, the different challenges were addressed during the application of RWH practices in the field, including pond siltation, seepage losses, water lifting problems, and lack of awareness, which were the major ones. These challenges will be reduced when all concerned bodies can participate in the technology at the local level. Therefore, rain-fed agriculture’s ability to increase crop production in the study region has in general demonstrated a significant impact.

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Meskele, D.Y., Shomore, M.W. & Adi, K.A. A review on harvesting rainwater for agricultural production in the rain-fed region, Ethiopia: challenges and benefits. Sustain. Water Resour. Manag. 9 , 176 (2023). https://doi.org/10.1007/s40899-023-00957-5

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