Univariate Time Series Analysis Of Rainfall In Somali Region Ethiopia

Rainfall is one of the most significant sources of water on earth, supporting thernexistence of the majority of living things. It is such a critical variable, particularlyrnthose whose livelihoods depend on rain-fed agriculture. Statistical approaches such asrntime series analysis give a way for analyzing and forecasting the patterns of rainfall. Inrnthis study, we have attempted to analyze the pattern of rainfall in the Somali region.rnFor this purpose, a monthly rainfall data of 26 meteorological stations covering thernregion for 34 years of gridded 0.4o *0.4o resolution have been used. A univariaternBox-Jenkins approach was used to build a seasonal ARIMA model to determine thernrainfall pattern of the region. Descriptive results show that, during the years in thisrnstudy, the mean annual and monthly rainfall series in the region are 567mm andrn34.9mm respectively, with a higher year-to-year variation (CV > 0.30). It also showsrnthat the region has two rainy periods April-May and August-October, followed byrna prolonged dry season. Using Box-Jenkins approach we have obtained a seasonalrnARIMA (1,0,1)(2,1,2)12 model and then used to establish an 80% and 95% predictionrninterval to forecast a 5 year monthly rainfall values. The forecasting results revealedrna very slight decrease of monthly rainfall over the forecast period from January 2017rnto December 2021.

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