Impact of climate change on potential evapotranspiration and crop water requirement in Upper Wabe Bridge watershed, Wabe Shebele River Basin, Ethiopia

This study intended to estimate the potential evapotranspiration (PET) and crop water requirement (CWR) under climate change in Upper Wabe Bridge watershed. Precipitation and temperature data were projected using the mean of three Regional Climate Models (RCMs) derived by three General circulation models (GCMs) via Coordinated Regional Climate Downscaling Experiment (CORDEX) Africa of Representative Concentration Pathways (RCP4.5 and RCP8.5) scenarios. PET was computed by using the Hargreaves equation. The results confirm a variability of PET by interchanging of excess and deficit at all stations. The average annual PET slowly increases and becomes it's extreme on 2100 under RCP8.5 scenario at all stations. However, under RCP4.5, the PET's become high at the start of midterm, and then start to decline and reach its minimum value at the end of the long term. The rates of changes vary from 19.9 to 28.5% under RCP8.5 and, 14.3 to 15.3% under RCP4.5 at Kofele, and 11.8 to 6.8% under RCP4.5 and 16.3 to21.1% under RCP8.5 scenario at Sire station from midterm (2040-2070) to long-term (2071-2100), respectively. The annual average PET varies from 37.6 to 49.2% in RCP8.5, but decreases from 30.1 to 15.4% in RCP4.5 climate scenario at Kofele station. In Kiremt season PET decreases from the mid-2050s to long 2080s terms under both climate scenarios. The outcomes showed that CWR showed also a similar trend as PET. The increasing trends in PET will rise the irrigation water requirement and as a result, need to revise water resource development and water allocation policies in the watershed.