METEOROLOGICAL DROUGHT ANALYSIS: THE CASE OF ABAYA- CHAMO SUB-BASIN

Abstract

Meteorological drought is the deficit in precipitation over a region for a period of time which in turn results in the reduction of moisture condition of the soil and then the crop yield. It has severe socio-economic and environmental impacts which require to careful monitoring of drought conditions using a suitable index. The objective of this research was to analyze meteorological drought frequency, severity and duration in the Abaya-Chamo Sub-basin using the application of SPI for monthly rainfall records. After checking the data quality and fitting the Gamma statistical distribution for each selected station as a requirement of the SPI, the analysis was done for the past 30 years of record from 1988 to 2017 for five selected stations based on monthly precipitation records using the index at 1-, 3-, 6-, 9- and 12-month timescales. The results show that, no correlation exists between successive observations, and thus, the data are independent, and there was no persistence in the time series. The inter-site correlation was less than one (R2<1) for all the statios and hence all the stations in the sub basin were consistent. For both convectional Cv and L-Cv based homogeneity tests the coefficient of correlation (CC) values were less than 0.3 showing the homogeneity of the stations. Gamma probability distribution was determined as the best fit statistical distribution for the data set since the typical alpha level was greater than 0.05 at 95% of confidence interval as checked using Kolmogorov Smirnov and Shapiro Wilk’s test using SPSS. All of the studied meteorological stations experienced drought episodes in 1988, 1989/1990, 1992/1993, 1999,2000/2001, 2003/2004 and 2007/2008 which were among the worst drought years in the history of Ethiopia, and moderate drought events ranging from the SPI values of -1.49 to -1 were pronounced with greater frequency than other dry events. Severely dry events were occurred at values between -1.99 and -1.50. The maximum SPI value of extreme dry event was -2.69. The year 1999 was the most drastic and distinct-wide extreme drought episode in all studied stations. The findings of this study have implications for drought management, early warning system, preparedness and contingency planning and climate change adaptation