Abstract:
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.
