Climate Pattern and Recurrent Drought of Mieso Area, West Hararghe, Ethiopia

Drought can generally be defined as the persistence of precipitation deficit. It can range from mild to extreme depending on the severity of the lack of precipitation. The area around Mieso during the times of benign years is known and praised for its abundant sorghum production. But over last couple of decades, it is persistently affected by drought and consistently demanding grain charity. This study attempts to investigate the cyclic pattern and severity of the drought and its link to the atmospheric teleconnections. For this study, data from three closest meteorological stations (Mieso, Chiro and Hirna) were obtained and analyzed. Out of the three stations Chiro station data were found to be slightly similar to Mieso data. For the data analysis Mieso data was used with missing years data filled in from the analyzed Chiro rainfall data. The analyses were made using Dekadal Dryness Indicator (DDI), Start of Season (SoS), Runs theory, the Standard Precipitation Index (SPI) and the Standard Precipitation and Evapotranspiration Index (SPEI). The rainy seasons selected for the analysis were Feb.-May (the short rainy season) and June – Sept. (the main rainy season) separately and by combining the two seasons. Besides, the drought years were related to global atmospheric and oceanic teleconnections. The averaged rainfall results revealed the 2nd dekad of March and the first dekad of July as start of season (SoS) for the two rainy seasons, respectively. The ecadal results showed the lengths of the two rainy seasons to be three months or less. The run theory exhibited drought intensities of -89 mm, -117 mm and -108 mm during the years 1991-93, 2002-2003 and 2008/2009, respectively. Based on SPI analysis, the seasons (MAM and JAS) each had one extreme and one severe drought years. MAM rainy season experienced two while the JAS rainy season had four moderate drought years. The combined six months rainy season experienced 2 severe and six moderate drought years. SPEI showed identical drought years (2002 extremely severe and 2008 severe) withSPI. The severe droughts of the two seasons seem to have 10 year cycles and the moderate dry years came six years after the severe drought years. Nearly 50% of the time there were start of season failures, which partly contributed to the drought. The droughts were generally stronger during El Nino years dominated by El Nino dominance period and when ENSO was positive. Since it is roughly possible to predict these events, it is possible to roughly predict the drought years but it may still be difficult to predict the intensities