Spatio-temporal actual evapotranspiration estimation under climate change scenarios in the Weyib Watershed, Ethiopia

Climate change significantly impacts actual evapotranspiration (AET) on a spatio-temporal scale; it is vital to comprehend its effects on water resource availability. There was a limited understanding of estimating spatio-temporal AET in the study area through the ensembling of numerous climate models. This study aimed to predict the effects of climate change (spatio-temporal) on AET for Weyib watershed using two Representative Concentration Pathways (RCP) scenarios (RCPs 4.5 and 8.5). The five climate models were bias-corrected and ensembled, and verified WetSpass-M model was used to estimate AET. Then, AET was estimated over baseline (1986–2015), mid-term (2031–2060), and long-term (2071–2100) periods for both RCP scenarios. The results showed that future mean temperature and rainfall will have an increasing pattern for the RCP4.5 and RCP8.5 scenarios, compared to the baseline period. The findings indicate that the annual AETs during the baseline period were 608.20 mm/yr, increasing by 7.30% for MidT4.5 (Mid-term for RCP4.5), 10.19% for LongT4.5 (Long-term for RCP4.5), 3.47% for MidT8.5 (Mid-term for RCP8.5), and 18.50% for LongT8.5 (Long-term for RCP8.5). A future seasonal AET is expected to rise throughout winter, spring, and summer, while declining in autumn compared to the historical period. Furthermore, the monthly average percentage variations of AET were 8.70, 18.22, 6.53, and 36.09% for each scenario, respectively. This study's findings showed that climate change causes a considerable increase in AET, while negatively affecting agricultural productivity and water resource availability. This will require implementing innovative agricultural practices and sustainable water resource management plans to mitigate the adverse effects of climate change.