Precipitation Moisture Sources of Ethiopian River Basins and Their Role During Drought Conditions

Abstract

In this study, we identified and investigated the annual climatological moisture sources for the Ethiopian river basins during 1980–2018. First, according to cluster analysis, the 12 river basins of this country were grouped into four regions: northeast (NE), southeast (SE), southwest (SW), and west (W), which were characterised by similar annual precipitation features. Global outputs from the Lagrangian FLEXPART model were used to investigate the air mass humidity gain before reaching each region. This revealed five main oceanic moisture sources located in the Mediterranean Sea, Red Sea, Indian Ocean, Persian Gulf, and the Arabian Sea, in addition to three main terrestrial moisture sources located in the African continent, Arabian Peninsula, and the regions themselves. Once the main climatological sources of moisture for each region were identified, a forward-in-time analysis of air masses over each source was performed to calculate the moisture contribution to precipitation (E – P) < 0 over the defined regions. The most important source at the annual scale for the NE, SW, and W regions is the African continent, while for the SE, it is the Indian Ocean. Indeed, terrestrial moisture sources are the major contributors (>50%) to the precipitation over the NE, SW, and W, whereas oceanic sources are the major contributors to the SE. Another analysis identified the years affected by drought conditions in the regions. The role of the sources was evaluated for those years affected by severe and extreme drought, revealing the heterogeneous and also direct influences on the regions. Finally, according to the normalised difference vegetation index, the impacts of annual severe and extreme droughts were more prominent in areas of the NE and SE, but also in the SW during 1984.

The phenomenon of drought in Ethiopia: Historical evolution and climatic forcing

“…This is also observed for other basins such as the Rift Valley during 1998 and 1999, when it was affected by extreme drought conditions, but basins to the north and south of it were affected by dry conditions of lesser magnitude. Differences in drought severity and drought affliction periods are also observed between basins with similar rainfall regimes such as the Abbay and Baro, or Genale, Wabi-Shebelle, and Ogaden (Stojanovic et al 2022). These results suggest that despite the homogeneity in rainfall regimes among some of the major basins in Ethiopia, drought phenomena differ in frequency and severity when basins are considered individually.…”

“…In addition, historical droughts the country faced in the past four decades such as 1984, 2002, 2009, 2011, and 2015 are appreciated at various temporal scales of both the SPI and the SPEI. Stojanovic et al (2022) utilized other precipitation and evapotranspiration datasets (CRU TS v4.05) and also found the affectation of extreme dry conditions in the northeast, southeast, and southwest of the country during in 1984, which was associated with a reduction of moisture transport from oceanic and terrestrial sources and divergence of the moisture flux. They also found the affectation of the northeast and west major river basins in 2009.…”

Hydrological drought forecasting and monitoring system development using artificial neural network (ANN) in Ethiopia

“…Baro Akobo and Omo Gibe River basins are received rainfall twice a year and have good climate condition compared to other river basins [ 69 , 70 ]. Although they received good rainfall, hydroclimatic disasters such as floods and droughts occurred in different parts of the basin [ 69 ]. But comprehensive drought studies were yet studied in both Baro Akobo and Omo Gibe River basins.…”

Vegetation Greenness Sensitivity to Precipitation and Its Oceanic and Terrestrial Component in Selected Biomes and Ecoregions of the World

“…In Africa, two differentiated regions are situated on the coast of West Africa and Ethiopia, where the VGS to PLT without eliminating and after eliminating the joint effect of temperature and radiation is higher than in the rest of the ecoregions of that continent. In both regions, the oceanic contribution to precipitation is higher and directly modulated by the moisture supply from the Gulf of Guinea [106,107] and the western Indian Ocean [108,109], respectively. Vegetation in both regions is therefore more sensitive to slight changes in precipitation of terrestrial origin.…”