Climate Variability and Drought in the Past 30 Years in Central Rift Valley of Ethiopia

Abstract

The study carried out in order to analyze climate variability and drought in Rift Valley of Ethiopia. Hence, a number of analyses, such as: the Precipitation Concentration Index (PCI) and Coefficient of Variation (CV) methods are used for rainfall variability, Markov chain second order method were used in order to analysis dry spell length, while standardized rainfall anomaly were used for drought severity class. From the analysis the annual rainfall was less variable for all stations; while the seasonal variability was higher as computed using both PCI and CV methods. When the main rainy season variability was compared with the second rainy season “Belg”, the second rainy season was more variable for all stations. As a result, PCI value showed that Belg rainfall varied from moderate concentration to high concentration. By using INSTAT software, the historical onset and cessation date and characteristics of dry spells were investigated. It is understood that the main rainy season starts on the 174th day of the year and stops on the early second decade of September. But the variability of onset rainfall is high it may lag up to 1 month while cession data is not exceed 15 days for all stations. The 5 day probability of dry spell in the area is more than 75% even during rainy season, while 30 day dry spell is not exceed 50% even during dry season. Most of the drought years were associated for each station; even if for some station the occurrence of drought year varies by one year. But 1965, 1972-73, 1978, 1980, 1984, 1994, 1995, 2001-02, 2009 and 2014/15 show that almost all station indict there was drought index in the study area even though the drought severity degree was different. The drought frequency and intensity in central rift valley of Ethiopia is increasing trend, among 31 severe droughts 21 of them happened before 1980.

Keywords: Rainfall variability, Drought, SPI, PCI, Dry spell