Evaluation of Hydrological Drought Under Climate Change in Hamessa Watershed, Rift Valley Basin, Ethiopia

Abstract

Drought in the Hamessa watershed may result from water scarcity brought on by extended periods of decreased rainfall as a result of climate change. However, so far hydrological drought analysis was not done in this watershed. Therefore, the aim of this study was to evaluate hydrological drought in the Hamessa watershed under climate change. Soil and Water Assessment Tool (SWAT) was used to model the watershed, and SWAT‐CUP (Calibration and Uncertainty Procedures) was used for sensitivity, calibration and validation of the model. A watershed’s drought conditions and areas that are susceptible to drought are determined by the standard precipitation index (SPI) and the streamflow drought index (SDI). The long‐term and short‐term temperature projections under the RCP2.6 and RCP8.5 scenarios show an increase over the current period. In the meantime, precipitation forecasts indicate a decline in both scenarios for the years 2040–2072. The model’s performance reveals that R 2 , NSE, and PBIAS were 0.79%, 0.78%, and 1% during calibration and 0.76%, 0.78%, and 6.1% during validation, respectively. These showed that the outputs from simulations and observations agreed very well. The watershed is currently experiencing mild, moderate, severe, and extreme drought events, according to the results of the SDI and SPI. In the RCP2.6 and RCP8.5 scenarios, droughts are predicted to occur in the years 2040–2060 and 2061–2072. The results indicated that the watersheds were highly vulnerable to severe and extreme drought. Consequently, in order to alleviate drought in the watershed, drought‐mitigating structures are required like the construction of reservoirs and water harvesting structures.