Impacts of climate change on blue and green waters in Tekeze-Atbara watershed, Nile basin

This study examines the impacts of climate change on blue water flow (BWF), green water storage (GWS), and green water flow (GWF) components of water resources in the Tekeze Atbara watershed of the Nile basin. It employed five CMIP5 climate models under RCP4.5 and RCP8.5 scenarios along with a satisfactory SWAT model with acceptable predictive uncertainty. The results indicate that while mean annual changes in BWF (stream flow) and the green waters remain stable (p > 0.05), considerable decline in all water components during the Belg season and spatially in the northeastern sub-basins of the watershed are projected. Moreover, statistically significant (p < 0.05) changes in inter-annual variability, particularly for the green waters are projected with variability in BWF remaining high. One of the key findings of this study is the distinction between GWS (soil moisture) and GWF (actual evapotranspiration), revealing a decrease in both, in contrast to recent studies that suggest an increase in semi-arid regions when aggregated. This study highlights the critical need for localized and integrated water management strategies addressing both blue and green waters in the changing climate. Future research should integrate land use and water use scenarios to enhance the robustness of such assessments.