Rainfall Variability in the Ethiopian and Eritrean Highlands and its Links with the Southern Oscillation Index

Abstract

Drought-prone tropical African regions are characterized by a high variability of seasonal and annual rainfall across time and space. Part of this variability is known to be associated with the El Niiio-Southem Oscillation (ENSO) phenomenon: e.g. main rainy season droughts in Ethiopia are more likely to occur during the years of warm ENSO events. In this paper we present teleconnections between the monthly SO index (SOI) and the monthly regional rainfall indices of the north central Ethiopian and Eritrean highlands over the reference period 1900-90. The monthly Darwin sea level pressure (DSLP) data are used as a 'proxy' for SOI. Rainfall of sub-Saharan West Africa is compared with the rainfall of the north central Ethiopian and the Eritrean highlands for the two periods 1945-64 and 1965-84. The Blue Nile flow measured at Khartoum is also compared with its sub-catchment rainfall over the north central Ethiopian highlands. The possible links of the decreasing summer rainfall over the last 30 years with the terrestrial ecosystems and the land-use and land cover changes in this region of Africa will be evoked.