Drought is a complex natural phenomenon that affects life and natural resources. It is needed to understand the drought events to take adaptation and mitigation measures. Thus, the objective of this study is to analyze the temporal and spatial patterns of multiscalar drought events at 20 stations in the Upper Omo-Gibe River Basin (UOGRB) for the period of 1981 to 2016. Mann-Kendall, Sen’s slope estimator, Pettit test, and two drought indices SPI/SPEI at 1-, 3-, 6-, 12-month time scales were used to evaluate the drought events. The mean annual rainfall decreased significantly at the rate of -4.505mm/year.Annual Tmean increased significantly by the rate of 0.034℃ /year. In this sub-basin severe drought events were observed in the years1987, 2004, and 2012. During this study period, the drought values ranged from -2.67 to -3.78 for SPI and from -2.139 to -2.426 for SPEI with different time scales. Both drought indices show the occurrence of extreme drought events over the area from 1999 to 2016. The study provided a scientific basis for revealing the spatial and temporal distribution of drought in the UOGRB basin.

Keywords: Mann-Kendall, multiscale, Pettit test, SPI, SPEI, Sen’s slope estimator