Recent changes in rainfall and rainy days in Ethiopia

Abstract

Changes in annual, June-September and March-May rainfall and rainy days herein (defined as a day with rainfall greater than 1 mm) have been analysed based on 11 key stations located in different climatic zones of Ethiopia over the common period . The progressive Mann-Kendall trend test shows that there is no trend in the annual rainfall total, the seasonal rainfall total or rainy days over central, northern and northwestern Ethiopia in the period . In contrast, the annual and the June-September total rainfalls for the eastern (Jijiga, 137 mm/decade), southern (Negele, 119 mm/decade) and southwestern (Gore 257 mm/decade) stations show a significant decline since about 1982. Correlation analysis shows that the decline of rainfall in eastern, south and southwestern Ethiopia is caused by the corresponding persistent warming of the South Atlantic Ocean over the period approximately from 1986 to 2002. The sea-surface temperature (SST) over the tropical eastern Pacific Ocean is not significantly correlated with the main rainfall of the semi-arid lowland areas of eastern, southern, and southwestern Ethiopia, except at marginal zones in transition to the Ethiopian Highlands.June-September rainfall over the Ethiopian Highlands is positively correlated to the equatorial east Pacific sealevel pressure and the southern oscillation index, and negatively correlated to SST over the tropical eastern Pacific Ocean as expected, confirming again that warm El Niño-southern oscillation episodes are associated with below-average June-September rainfall over the Ethiopian Highlands.

Defining high-flow seasons using temporal streamflow patterns from a global model

“…The first and most common is the annual-maximum (AM) method, which samples the largest streamflow in each year. The second method is the peaks-over-threshold (POT) method (Smith, 1984(Smith, , 1987Todorovic and Zelenhasic, 1970), in which all distinct, independent dominant peak flows greater than a fixed threshold are counted. In contrast to the AM method, POT can capture multiple large independent floods within a single year, including the annual maximum flow, but may not capture the annual maximum flow in years in which streamflow is less than the pre-defined threshold; this threshold can either be defined based on a specific average number of floods or a specific mean exceedance level over the entire period (Cunderlik et al, 2004a;Institute of Hydrology, 1999;Lang et al, 1999).…”

“…For example, eastern Africa has two rainy seasons, the major season from June to September and the minor season from January to April/May. These two seasons are induced by northward and southward shifts of the Inter-tropical Convergence Zone (ITCZ) (Seleshi and Zanke, 2004). This bi-modal eastern African pattern allows for potential flooding in either season.…”

Spatial and temporal variability of rainfall in the Nile Basin

“…For group B, it is also shown from Table 4 that influences also are obtained from Niño 3, the Indian Ocean and as far as the extra-tropical Southern Hemisphere. The annual rainfall in Sudan and Ethiopia (group B) has been shown in a number of studies to be influenced by the El Niño-Southern Oscillation (ENSO); see Osman and Shamseldin (2002) for Sudan; Fontaine and Janicot (1992), and Grist and Nicholson (2001) for the Sahel belt; Abtew et al (2009), Beltrando andCamberlin (1993), Diro et al (2010), Korecha and Barnston (2007), Seleshi and Demarée (1995), Segele and Lamb (2005), and Seleshi and Zanke (2004) for Ethiopia.…”

Large‐scale atmospheric circulation and global sea surface temperature associations with Horn of Africa June–September rainfall

“…The authors noted that improvements in understanding the basic circulation patterns across Africa are essential for improving the management of socio-economic activities affected by climate variability and future climate change, not only in Africa but also on a more global scale. Because the large-scale atmospheric circulation is directly linked to many aspects of regional climate variation (Beck et al, 2007), investigation of the links between atmospheric circulation patterns over Africa and rainfall there and elsewhere is important for understanding For example, although the large-scale circulation systems during the Indian summer (south-west) monsoon generally are associated with concurrent rainfall over the Horn of Africa (Krishnamurti and Bhalme, 1976;Conway, 2000;Gissila et al, 2004;Seleshi and Zanke, 2004;Korecha and Barnston, 2007), only a few quantitative studies have linked those circulation systems specifically to local weather and climate patterns over the Horn of Africa (e.g. Beltrando and Camberlin, 1993;Camberlin, 1997;Shanko and Camberlin, 1998;Block and Rajagopalan, 2007).…”