Analysis of rainfall climate and evapo-transpiration in arid and semi-arid regions of Ethiopia using data over the last half a century

Rainfall and evapo-transpiration are the two major climatic factors affecting agricultural production. While rainfall can be directly measured, evapo-transpiration is estimated from weather data. In this study reference evapo-transpiration ETo was estimated using Penman'Monteith equation, under full data and limited data availability conditions, and Hargraves method. Monthly rainfall and evapo-transpiration were plotted and compared in order to determine moisture deficit periods for several stations in arid and semi-arid parts of the country. Rainfall and reference evapo-transpiration at different probability levels were compared. Temporal variation of annual rainfall was analysed using variability indices:cumulative departure index, standard climate departure index and rainfall anomaly index.It was found that when there is only limited data, it is better to estimate ETo using Penman'Monteith method than using simplified methods such as Hargraves. ETo showed relatively low variation with time while year-to-year rainfall variability was very high. From these plots information on rainfall pattern over the past 50 years, such as drought years was obtained.