Long-term hydroclimatic variability over the semi-arid highlands of Ethiopia in relation to ENSO and IOD teleconnection signals

Abstract

Studies on global effects of ENSO (El Niño Southern Oscillation) and IOD (Indian Ocean Dipole) to local patterns of rainfall and streamflow (hydroclimatic) variability is limited. The focus of this study is to understand the influence of large-scale indices of ENSO and IOD on hydroclimatic variability of the upper Tekeze basin Giba catchment (GC) where located in the northern highlands of Ethiopia. Modified Mann–Kendall and Pettit tests were used to generally understand the overall trends and expected abrupt changes of rainfall and streamflow in the GC hydroclimate. We also used correlation and multiple regression analysis to oversee the linkages, performance and strengths of SSTs (sea surface temperature) to the local hydroclimate variabilities. Our results show the abrupt changes strongly linked with the El Niño years. We also found ENSO and IOD plays a crucial role in modulating the local hydroclimate variability of GC, and that ENSO plays a more important role than IOD. The main rainfall season JAS (July-August-September) in GC is positively correlated with March to May SST in the western Pacific Ocean, eastern Atlantic Ocean, Northern Atlantic and southwestern Indian Oceans. And, the JAS rainfall is negatively associated with March to May SST in Southeast Indian Ocean which results a decrement in JAS rainfall. The long-term streamflow variations across the study period strongly correlated with rainfall variability in all the stations. This highlights a signature to takeover different decisions at local level of the upper Tekeze basin GC for a better water resources development and management.