Impact of climate change on surface water availability and crop water demand for the sub-watershed of Abbay Basin, Ethiopia

In the present study, climate change effects on surface water availability and crop water demand (CWD) were evaluated in the Birr watershed (a sub-watershed of Abbay Basin), Ethiopia. The Coordinated Regional Climate Downscaling Experiment (CORDEX)-Africa data output of Hadley Global Environment Model 2-Earth System (HadGEM2-ES) was selected under the representative concentration pathways (RCP) scenarios. The seasonal and annual streamflow trends in the watershed were assessed using the Mann–Kendall (MK) test and Sen’s slope at 5% significance level. The surface water availability was assessed using the Hydrologiska Byråns Vattenbalansavdelning (HBV) model. The HBV model showed a satisfactory performance during calibration (R² = 0.89) and validation (R² = 0.85). The future water availability was simulated under climate change scenarios. The future projected streamflow indicates that minimum flow may decrease under RCP4.5 and RCP8.5 scenarios, revealing significant downward shifts in the years 2035 and 2055, respectively. Similarly, the 1 day and 7 days maximum flow under RCP8.5 and 90 days flow under RCP4.5 are expected to decrease significantly and a considerable shift may occur in the 2060s and 2030s, respectively. Contrarily, both the minimum and maximum flow may not change significantly under the RCP2.6 scenario. Current and future water demand for the maize crop was estimated using the CROPWAT. The result indicated that irrigation water requirement (IWR) for maize crop may be increased throughout the growing periods, especially, during the development stage. Therefore, this study may contribute to the planning and implementation of the sustainable water resources development strategies and help to mitigate the consequences of climatic change, especially on commonly grown crops in the region.