Spatiotemporal analysis of droughts characteristics and drivers in the Omo-Gibe River basin, Ethiopia

Background: Drought is one of the leading destructive natural disasters adversely affecting natural resources and livelihoods. Thus, this study evaluated the spatial and temporal meteorological drought characteristics and their drivers in the Omo-Gibe River basin (OGRB) from 1981 to 2017. The drought analysis used the standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) with 4- and 12-month timescales. The Mann–Kendall (MK), Sen's slope estimator, and Pettit test were used to evaluate the trend and change points of the time series. Pearson correlation was used to examine the teleconnection between large-scale global climate signals with the basin's seasonal and annual drought indices. Results: Accordingly, extreme and severe drought events were observed in 1988, 2000, and 2009. In the basin, prolonged drought events were recorded from 2000 to 2015. The statistically significant (P < 0.05) increasing trend of seasonal and annual drought events was observed in all basin parts. However, more drought events distribution was exhibited in the south than in the north and central parts. The Sawla station (southern part) showed a higher drought frequency, ranging from 18.18 to 20.36%. The maximum intensity and peak drought events were observed in this sub-basin, with SPEI reaching − 2.27 and − 4.89, respectively. The global indices NINO3.4, SOI, and DMI are drivers for triggering the meteorological droughts in OGRB. Conclusions: Substantial warming and erratic rainfall have made OGRB vulnerable to drought events. The intensification of droughts in the basin has also been recorded in humid parts of the basin which has a significant adverse effect on the water availability of down streams. This indicates that the observed drought intensity can increase the water deficit and other natural resources degradation. Therefore, this study provides essential information on drought characteristics for decision-makers to plan appropriate strategies for early warning systems to adapt and mitigate drought hazards in the basin.