Climate change significantly impacts agricultural production globally, with low-latitude regions facing the most adverse effects. Decreasing crop yields coupled with rising food demands, exacerbated by factors like the COVID-19 pandemic and the war in Ukraine, pose a critical challenge, particularly in Africa. Sustainable intensification, involving increased investment in technology and higher water/fertilizer inputs, offers a potential solution. However, the extent to which this intensification might exacerbate water resource pressures and the limitations imposed by climate change remain unclear. This study addresses this gap by developing spatially explicit future scenarios of crop water footprint in Africa, exploring the implications of significant yield growth under changing climatic conditions. The study assumes increased crop productivity to reach maximum attainable yields by 2040, driven by intensive agricultural management and expanded irrigation infrastructure. The crop water footprint (CWF), encompassing both green (soil moisture) and blue (irrigation) water, serves as a key indicator to analyze the water-food nexus. Previous research has focused on global or national/basin-level CWF projections. This study provides high-resolution (5 arc min) sub-national scenarios under RCP 2.6 and RCP 6.0 for 2040, 2070, and 2100, using 2010 as a baseline. The WaterCROP model is utilized, integrating future projections of crop evapotranspiration and yield for twelve major crops. A 'hard-intensification' pathway, aligned with SSP5, assumes maximum attainable yields with constant harvested areas (2010 levels). This optimistic scenario is compared to an 'extensification' pathway (SSP2), extrapolating from current trends of harvested area expansion.

Existing literature highlights the significant impact of climate change on global agricultural production, with low-latitude regions, including Africa, facing the most severe consequences. Studies project decreased crop yields under future climate scenarios due to rising temperatures, altered precipitation patterns, and increased drought frequency. Simultaneously, global food demand is increasing, driven by factors such as population growth, rising affluence, and biofuel production. Various strategies have been proposed to address this challenge, including sustainable intensification, which aims to increase yields while minimizing environmental impacts. However, questions remain regarding the water resource implications of this approach, especially in water-stressed regions like Africa. Previous studies have explored future global or regional CWF scenarios but lacked the high spatial resolution needed for detailed regional analysis. This study builds upon this existing research by offering high-resolution, spatially explicit scenarios of crop water footprint in Africa, examining the interplay between climate change and agricultural intensification.

This study utilizes the WaterCROP model to generate spatially explicit scenarios of crop water footprint (CWF) at a 5-arc minute resolution across Africa. The model combines projections of crop evapotranspiration (ET) and yield for twelve major crops (barley, cassava, cotton, groundnut, maize, millet, rice, sorghum, soybean, sugarcane, wheat, and yam) with climate data. Future climate data were obtained from the ISI-MIP repository (simulation round ISI-MIP2b), encompassing RCP 2.6 and RCP 6.0 for the periods 2011–2040, 2041–2070, and 2071–2100. Precipitation (P) and reference potential evapotranspiration (ET0) projections were downscaled to 5 × 5 arc min resolution and averaged over 30-year intervals. These projections were then ‘anchored’ to observed climate data (CRU CL v. 2.0 and FAO data for 1961–1990) by adding the difference between the future and historical projections to the observed data. Crop-specific information on yields and harvested areas was sourced from the Global Agro-Ecological Zones (GAEZ v4) database. GAEZ v4 provides both actual (2010) and attainable yields, incorporating assumptions about future agricultural management practices (high inputs, optimal irrigation). Two scenarios were modeled: a 'hard-intensification' pathway assuming maximum attainable yields with constant harvested areas (2010 levels) and an 'extensification' pathway extrapolating from current area expansion trends. WaterCROP calculates daily crop-specific actual evapotranspiration (ETa) based on climate data, phenology, and agricultural practices. It distinguishes between green (rainfall) and blue (irrigation) water components of ETa, allowing for the calculation of green and blue water footprints (WF) both in total volume and per unit of production (uWF). The study also employs indicators of water stress (average water stress coefficient, ks) and food security (caloric yield), comparing them with food insecurity data from FAOSTAT. Uncertainty analysis acknowledges uncertainties in yield projections, evapotranspiration estimates, and model assumptions.

The study found that a high-input agricultural management strategy coupled with expanded irrigation infrastructure could lead to a significant reduction in water use intensity (up to 64%) for staple crops by 2040, under the hard-intensification scenario. However, this reduction was only 5% for cash crops. Despite the positive effect of intensification on water use efficiency, substantial additional blue water resources (82–102 km³ between 2040 and 2100) would be required to sustain the projected yield increases. Spatial analysis revealed that green water footprint (rainfall contribution) increases are mainly observed in the equatorial zone where soil moisture is sufficient to meet the growing demand, while negative changes were seen in northern and eastern Africa due to increased water stress. The blue water footprint, driven by irrigation expansion, increased substantially across Africa under the hard-intensification scenario. The unitary water footprint (uWF) showed large decreases for most crops by 2040 due to the steep increase in yields. Cash crops consistently exhibited higher blue water uWF compared to staple crops, highlighting their reliance on irrigation. Analysis of water stress (ks) showed that wetter conditions are projected for some regions (Gabon, Uganda), but drier conditions are expected in northern Africa and several food-insecure countries. Caloric yield is projected to increase substantially under the hard-intensification scenario, especially in food-insecure countries, but this increase is unevenly distributed. Comparison of hard-intensification and extensification pathways revealed that extensification leads to higher overall water use due to lower water use intensity. However, some crops showed significant uWF reduction under both scenarios, suggesting potential for improved water use efficiency regardless of management strategy.

This study's findings highlight the complex interplay between climate change, agricultural intensification, and water resource management in Africa. While high-input agricultural practices can enhance water use efficiency for staple crops, the reliance on blue water resources raises concerns about water sustainability. The uneven distribution of yield increases and the projected changes in water stress underscore the need for targeted interventions to address food insecurity and climate vulnerability. The hard-intensification pathway, while achieving significant yield increases, comes at the cost of increased blue water demand and potential environmental risks associated with high input agriculture. The comparison with the extensification pathway emphasizes the trade-offs between intensive production and the potential for further environmental degradation. These results should inform policy decisions aimed at strengthening food security in Africa while ensuring sustainable water management. Strategies should consider balancing food production with environmental sustainability and social equity.

This study demonstrates that although efficient agricultural practices can reduce crop water footprints in Africa, even under climate change, the reliance on blue water resources for sustaining projected yield increases poses a challenge. The hard-intensification scenario highlights trade-offs between increased food production and potential environmental impacts. Future research should refine the models by integrating updated climate projections, exploring sub-national scale land expansion scenarios, and examining the role of international trade and local agricultural practices. These results underscore the necessity for holistic strategies to enhance food security while ensuring the sustainable management of water resources in Africa.

The study relies on several key assumptions, including the adoption of optimal irrigation and high-input agricultural practices by 2040, which might not fully reflect real-world conditions. The model's reliance on existing datasets introduces uncertainties related to future climate projections and crop yield estimates. The analysis focuses on water footprint, without explicitly considering other environmental and socioeconomic factors associated with agricultural intensification (e.g., energy use, fertilizer application, social impacts). The study's focus on a limited number of crops may not fully capture the diversity of African agriculture. Further research is needed to better understand the uncertainties involved and to broaden the analysis to encompass a wider range of factors.