Agro-climatic zone based hydrometeorological drought analysis and projection in Wabi Shebele river basin, Ethiopia

Abstract

This study aimed to analyze historical and projected hydrometeorological droughts in the Wabi Shebele basin using the SPI, SDI, aridity index and CMIP6 projections under SSP2-4.5 and SSP5-8.5. MIROC-6 and MPI-ESM1-2-LR best matched observed data. An ANN predicted future streamflow based on rainfall and flow data. The finding shows drought severity and frequency decline with longer timescales. Historical droughts with the longest drought duration of 15 months and the highest frequency (11.0–14.5%) every 2–3 years found in arid zones, semi-arid areas (3–4 years), midland zones (2–3 years) and highland zones (3–10 years). In contrast, the highland zone had lower frequencies of 8.3–14.3%. Under the SSP2-4.5 projections, semi-arid areas expected to exhibit the highest drought frequency of 15.4–21.3% with mean drought durations of 2.5 months. The highland zone projected to have the lowest frequency of 9–13.3% with low drought durations. Similar frequencies to baseline period are expected in arid and midland zones and increased occurrence in semi-arid and highland zones. The aridity index showed slight decrease in arid zone from 0.17 to 0.15 compared to future projection. ANN model performance for streamflow prediction of good to very good obtained. The projected hydrological droughts occur four times per decade compared to less than three per decade historically. Spatial analysis indicates that the middle and lower parts of basin are identified as drought hotspots area. Our results provide vital information for water management and agricultural planning based on drought hotspot areas.