Dry and Wet Spell Analysis of the Two Rainy Seasons for Decision Support in Agricultural Water Management for Crop production in the Central Highlands of Ethiopia

Rainfall remains the crucial component of the weather elements for improving agricultural yield in Ethiopia. Rainfall occurrence analysis is extremely helpful in planning of water resources and agricultural development. A study was conducted to asses the potential of sufficient rainfall occurrences and precipitation surplus and deficits in the central highland of Ethiopia for a selected district based on thirty three years of weather record data. The FAO(1978) and Reddy (1990) models were employed to set the threshold limits and the Weilbul frequency formula was used to calculate the probability of occurrences during the two growing seasons, belg(shorter) and kiremt (main). The results showed that the probability of occurrences of the sufficient amount of rainfall during the decades of main rainy season is promisingly stable while belg is observed to suffer from fewer occurrences of the sufficient amount even at the lower probability levels (25% probability of occurrences). Thus rainfall water harvesting during the main rainy season (Kiremt) is promising either for double cropping practices or other domestic uses. Key words: Frequency, Weibull, belg, kirem