Spatiotemporal analysis of drought in Oromia regional state of Ethiopia over the period 1989 to 2019

The Oromia regional state is significantly vulnerable to the impacts of drought. The majority of the population of the region is involved in agricultural and pastoral activities for their livelihood. Agriculture is predominantly dependent on the right onset, amount, period, and distribution of seasonal rainfall. Though there is abundant water resource in the region, irrigation contributes only 5% to produce agricultural products. This makes the region susceptible to the impacts of climatic extreme events such as drought. Yet, there are only a few studies on the spatial and temporal analysis of droughts over the Oromia regional state. This study examines the spatial and temporal characteristics of drought in the period 1989 to 2019 over the region using Standardized Precipitation and Evapotranspiration (SPEI) and Standardized Precipitation Index (SPI) drought indices. We assess temporal trends of drought over the region using Mann–Kendall trend test. We also assess the role of El Niño-Southern Oscillation (ENSO) in inducing seasonal droughts. Complex spatial and temporal patterns of drought occurrences are observed. The drought incidences at each of the stations have diverse magnitudes and durations. Drought during Belg season is more frequent over the southern and eastern parts of the region, whereas it is less frequent over the western and central parts. The spatial coverage of Belg droughts had increased over the study area since 1997 and decreased in recent years, particularly since 2016. On the other hand, drought during Kiremt season is more frequent over western parts of the region, whereas it is less frequent over southern and eastern parts. The year 2002 was the driest year with significant parts of the region having considerably severe Kiremt droughts. The years 1991, 2000, 2002, 2009, and 2015 were among the major drought years in the region; at least 34% of the region experienced annual droughts. There were 26 stations that showed increasing dry tendencies and 28 stations that showed wetting tendencies. Since a mix of signals in wet and dry tendencies exist in the region, clustering into homogeneous hydroclimatic zones is important in future studies. ENSO and seasonal drought over the region was found to be fairly associated.