Projected impacts of climate and land use changes on streamflow extremes in the upper awash Basin, Ethiopia

This study examines the projected effects of climate and Land Use and Land Cover (LULC) changes on streamflow extremes in the Upper Awash Basin (UAB), Ethiopia. Using high-performing CMIP6 climate models under SSP4.5 and SSP8.5, and future LULC scenarios under Business-As-Usual (BAU) and Governance (GOV) for the 2030s and 2060s, the SWAT model was employed to simulate hydrological responses. Results revealed that climate change significantly affects streamflow extremes, with high-flow indices; Maximum High Flow (MHF), counts of High-Flow Pulses (HPC), and duration of High-Flow Pulses (HPD) showing pronounced increases, while low-flow indices; Minimum Low Flow (MLF), counts of low-flow pulses (LPC), and duration of low-flow pulses (LPD) exhibited substantial declines. For instance, under SSP8.5 in the 2060s, MHF, HPC, and HPD increased by 63.16 %, 26.85 %, and 14.96 %, respectively, whereas MLF, LPC, and LPD decreased by 67.11 %, 34.40 %, and 5.95 %. In contrast, LULC changes demonstrated statistically nonsignificant effects on both high- and low-flow indices across all scenarios and periods. The BAU scenario projected substantial urban and cropland expansion, resulting in decreased forest and shrubland areas, while the GOV scenario emphasized sustainable land management, controlling urban sprawl and increasing forest cover. Despite these differences, LULC-induced changes in streamflow extremes remained marginal compared to the overwhelming influence of climate change. This study highlights climate change as the dominant driver of future hydrological extremes in the UAB, emphasizing the need for climate-focused adaptation strategies to mitigate adverse impacts on water resources and livelihoods in the region.