Hydro-meteorological drought predictions and trend analysis for ungauged watersheds in the Upper Blue Nile basin, Ethiopia, under future climate change impact scenarios

ABSTRACT Climate-change risks impact nations and it is essential to model climates to investigate potential meteorological and hydrological droughts at the selected ungauged watersheds (Gilgel Abay, Gumara, Megech, and Ribb). The Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) were used to analyze meteorological droughts for six- and 12-month periods and for hydrological droughts, the Streamflow Drought Index (SDI) was used. All indices were studied under near (2020–2049) and mid-future (2050–2079) periods using representative concentration pathways (RCPs) of 4.5 and 8.5 scenarios. The result shows that 18.10% of maximum hydrological drought (SDI12) frequency occurred for all scenarios and time-domains except RCP8.5 in the near-period. The highest drought annual time-scale (SPI12) and regional time-scale (RDI12) droughts were recorded at close intervals at 19.83% frequency under the near-period of both scenarios, respectively. The spatiotemporal distribution of meteorological drought at ungauged Megech is more vulnerable to extreme drought with the maximum magnitude recorded in SPI6 and RDI6 (about 3.5) by 2060 under RCP4.5. The SDI6 index also indicates that ungauged Gilgel Abay may experience acute drought shortly. This study is highly significant, particularly for climate researchers looking to implement climate-adaptation mechanisms in the Lake Tana sub-basin.