Future water availability and crop yields in Kenya’s Sand River Basin enhanced by elevated CO2 under climate change

The Sand River Basin, Kenya This study evaluates the combined impacts of future climate change and elevated atmospheric CO 2 on basin water balance and crop responses in the Sand River Basin using the SWAT+ model driven by ten General Circulation Models (GCMs) from ISIMIP3b. Simulations followed the SSP5–8.5 scenario for the near-future (2025–2054) and far-future (2070–2099) periods, comparing climate-only runs with simulations that include dynamically increasing CO 2 concentrations. Two crop cultivars were assessed: “non-adapted” cultivar and a “late-maturing” cultivar representing an adaptation strategy. Water availability is projected to increase toward the end of the century, particularly when CO 2 physiological effects are included, as reduced transpiration enhances soil moisture, runoff and percolation. Under far future CO 2 -enhanced conditions, water availability rises during both rainy seasons (e.g., +222 mm in MAM and +178 mm in ONDJ), and crop water and temperature stress decline. CO 2 -induced simulations also produced higher yields, with stronger gains for late-maturing cultivars. Yield improvements were greatest under combined climate and CO 2 effects in the far future (+7.6 % for maize; +10.4 % for beans), whereas climate-only simulations showed smaller increases. These findings highlight the importance of accounting for CO 2 physiological effects when assessing future hydrology and crop productivity and show that late-maturing cultivars represent a valuable adaptation strategy for strengthening agricultural resilience in the study region. • Water availability is expected to increase as atmospheric CO 2 levels rise. • CO 2 physiological effects on vegetation increased surface runoff and crop productivity. • Reduced growth constraints as projected temperature and rainfall benefit maize and beans. • Increases in CO 2 concentrations lead to higher yields for both maize and beans. • Late-maturing crops are projected to achieved higher yields than non-adapted crops.