Droughts related to quasi-global oscillations: a diagnostic teleconnection analysis in North Ethiopia

摘要

This study presents a method to elaborate atmospheric teleconnections and applies it on the drought-prone region of North Ethiopia. By doing so, the relatively new procedure known as empirical orthogonal teleconnection analysis (EOT) was validated as an effective way for identifying the impact of atmospheric patterns in remote oceanic basins on rainfall trends at a particular location. Rainfall trends were investigated, and trend analysis on optimally interpolated rain gauge data (1948-2013) shows no significant decrease for kiremt rainfall (June-September) in North Ethiopia. However, EOT analysis of assimilated mean sea level pressure data reveals that not only El Nino Southern Oscillation (ENSO)/La Nina, but also the Indian Ocean Dipole (IOD) has a significant impact in North Ethiopia. Including the variability of the Southwest Monsoons (SWM), subsequent multivariate regression could model North Ethiopian kiremt rainfall from these three teleconnections (R-2 = 0.64), representing 89% of all dry years. In particular, the interaction between these three teleconnections was a major contributor to the 1983-1985 droughts and famine. The study hence finds a significant impact of three atmospheric teleconnections (ENSO, IOD, SWM) on North Ethiopian rainfall variability. Moreover, it is pointed out that EOT analysis is a useful tool to identify the relations between drought risk and remote atmospheric systems.