Comparative analysis of hydro-metrological drought under global warming in middle Awash River basin, Ethiopia, case study of Kesem sub-basin

This study analyzed long-term hydro-metrological drought under climate change in the Kesem sub-basin, Middle Awash basin, Ethiopia. The comparative analysis was employed using three drought indices (the streamflow drought index, standard precipitation index, and reconnaissance drought index). These indices were evaluated using the ordinal by ordinal Spearman’s correlation, interval by interval Pearson, and kappa measure of agreement. The three drought indices have statistically significant (α < 0.01) strong correlation (> 0.78) and degree of agreement (0.2 fair agreement to 0.8 near-perfect agreement) tested at 99% confidence  interval. The potential evapotranspiration (PET) estimation shows an increase of + 25.9 mm (1.6%) from the base period to RCP 4.5 (2020) and + 26.7 mm (1.67%) to RCP 8.5 (2020), and + 55 mm (3.4%) to RCP 4.5 (2050) and + 56.8 mm (3.5%) to RCP 8.5 (2050). This increase in PET is an indication that the watershed is very susceptible to water deficit and drought in the coming periods. Mild to extreme hydro-metrological drought was experienced during the baseline period (1984–2010) and is projected to occur in the current (2011–2044) and future (2045–2075) periods under both RCP 4.5 and 8.5 emission scenarios at 6- and 12-month timescales. Droughts will likely become more frequent in the future in the study area. Currently, extreme droughts that last 6 and 12 months occur every 13 to 19 years. Under the RCP 4.5, these droughts could happen every 6–7 years by 2050. The RCP 8.5 suggests even more frequent extreme droughts every 14 years. These findings are substance information for the water users and development works in the basin including the Kesem dam reservoir.