Temporal and spatial characteristics of drought, future changes and possible drivers over Upper Awash Basin, Ethiopia, using SPI and SPEI

Drought is a global problem that affects particularly agricultural and water resources. The spatiotemporal drought characteristics and their possible drivers over Upper Awash Basin (UAB) were assessed in magnitude, duration, frequency, and intensity. Gridded data and a statistical downscaling model (SDSM) were used for historical projection. The Standardized Precipitation Index (SPI) and Standardized Evapotranspiration Index (SPEI) at 4- and 12-month timescales were used to compute the drought. The SPI 4-and 12-months indicate 1984, 1987, 2002, 2015, and 2016 years of dominant drought. Persistent dry events were observed in the west, northwestern, and some eastern parts of the study area in Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. Trend analysis of seasonal shows that a statistically significant (P < 0.05) increasing trend during the main cropping seasons and annual drought events were detected in almost all basin parts. Near future projections in the two (RCP4.5 and RCP8.5) scenarios exhibited the continuation of drought up to 2030s and mid-2040s extreme and severe dryness, respectively. The seasonal and annual analysis projection indicates a decrease in dry events from 2050 onwards. The detected periodicity of dryness/wetness agreed with the negative/positive phase of SOI/ ENSO (Nino3.4) during Belg and the positive/negative phase during Kiremt and annual (SPI4/SPEI4). The possible driving forces of these drought events were land use/cover changes such as land degradation and urbanization. Global indices IOD, SOI, and ENSO (NINO3.4) are drivers that caused the seasonal droughts. These findings are useful for better preparedness priorities that suggest developing basin-wide targeted interventions.