Evaluating The Role Of Indian Ocean Dipole On Seasonal Rainfall Performance Over Ethiopia

Abstract

Inter-seasonal rainfall variability over the Ethiopia was investigated with respect to Indian Ocean Dipole (IOD) and Indo-Pacific (IOD-ENSO). For better understanding of the nature of IOD and El Niño/Southern Oscillation (ENSO) influences on short rains, it is important to check the amplitude variation particularly during the years when flood or drought happened. The impact of IOD and ENSO were well investigated with the help of statistical analysis method. Statistical correlation between the IOD index and the global sea level pressure anomalies demonstrates that loadings of opposite polarity occupy the western and the eastern parts of the Indian Ocean. Besides the simple correlation method and a partial correlation technique were also used to show exclusive relationship between two variables while excluding influence arising from another independent variable. In order to make in-depth analysis, we considered parts of the country where Belg and Kiremt are the main rainy seasons. During Bega season, the country also receives less mount of rainfall but often very unseasonal that disturb harvesting season. We found that during bega season, rainfall performance over the country is clearly influenced by Indian Ocean Dipole (IOD) and/or ENSO. In contrast, during March-May, there is no clear inter-relation exist between seasonal rainfall and SST pattern in the Indian Ocean. As the result, the short rainy season over the country is not linearly related with selected extreme event of IOD years. The association between El Niño and positive IOD phases is much stronger than the association between La Niña and negative IOD during September to November. Further analysis is therefore required to pinpoint how the formation of strong SST anomalies over Indian and Pacific Oceans to explain seasonal rainfall variability, which in turn improves localized climate prediction over the country.