Abstract
Rainfall variability in Ethiopia has significant effects on rainfed agriculture and hydropower, so understanding its association with slowly varying global sea surface temperatures (SSTs) is potentially important for prediction purposes. We provide an overview of the seasonality and spatial variability of these teleconnections across Ethiopia. A quasi-objective method is employed to define coherent seasons and regions of SST-rainfall teleconnections for Ethiopia. We identify three seasons (March–May, MAM; July–September, JAS; and October–November, ON), which are similar to those defined by climatological rainfall totals. We also identify three new regions (Central and western Ethiopia, CW-Ethiopia; Southern Ethiopia, S-Ethiopia; and Northeast Ethiopia, NE-Ethiopia) that are complementary to those previously defined here based on distinct SST-rainfall teleconnections that are useful when predicting interannual anomalies. JAS rainfall over CW-Ethiopia is negatively associated with SSTs over the equatorial east Pacific and Indian Ocean. New regional detail is added to that previously found for the whole of East Africa, in particular that ON rainfall over S-Ethiopia is positively associated with equatorial east Pacific SSTs and with the Indian Ocean Dipole (IOD). Also, SST-to-rainfall correlations for other season-regions, and specifically for MAM in all regions, are found to be negligible. The representation of these teleconnections in the HadGEM2 and HadGEM3-GA3.0 coupled climate models shows mixed skill. Both models poorly represent the statistically significant teleconnections, except that HadGEM2 and the low resolution (N96) version of HadGEM3-GA3.0 better represent the association between the IOD and S-Ethiopian ON rainfall. Additionally, both models are able to represent the lack of SST-rainfall correlation in other seasons and other parts of Ethiopia.
Highlights
Rainfall is the most important climate element for rainfed agriculture and the general socio-economic development of Ethiopia (Conway et al 2011)
We find that correlations with the tropical Atlantic Dipole (TAD) and the equatorial east Atlantic (EqEAtl) are statistically non-significant, which contrasts with the interpretation of some previous studies (Segele et al 2009a, b; Diro et al 2011a) and requires further examination
This study has provided a general overview of the seasonal and spatial patterns of global sea surface temperatures (SSTs) teleconnections to Ethiopian rainfall variability using observed rainfall and SST data
Summary
Rainfall is the most important climate element for rainfed agriculture and the general socio-economic development of Ethiopia (Conway et al 2011). No study has been conducted for the southern Ethiopian September–November season, available studies conducted for the wider region of Equatorial East Africa (Saji et al 1999; Behera and Yamagata 2003; Black et al 2003; Marchant et al 2006; Saji and Yamagata 2003) show that anomalous warming (cooling) over the equatorial East Pacific and Indian Ocean are associated with enhanced (suppressed) rainfall amounts in this wider region All these studies imply that the SST-to-rainfall teleconnections in Ethiopia are both temporally and spatially complex and not yet well understood. The method that we applied to evaluate the performance of these models in this case study will be valuable for similar evaluations of other climate models
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