INTRA-SEASONAL RAINFALL CHARACTERISTICS IN FEDIS WOREDA OF EASTERN HARARGHE ZONE, OROMIA REGIONAL STATE, ETHIOPIA

Rainfall remains the crucial component of the weather elements for improving agricultural yield. Different models are used to explain the intra-seasonal features like water balance, Reddy model, Mann Kendal test, Markov Chain and Standard Precipitation Index. The water balance and Reddy models were used to analyze the variability and stability of onset, end and length of growing periods for common crops and soil conditions. The analysis of the annual rainfall was made by daily Precipitation software package to check the homogeneity and Double Mass curve to test the consistency of rainfall data of Fedis station. In Belg season the mean onset dekad was first dekad of April (dekad 10) and mean end dekad of last dekad of April (dekad12). However, the Belg season was found to be highly variable and insufficient amount of rainfall to meet dekadal crop water requirement in the area. The mean onset of the main growing season (Kiremt) was found to occur during second dekad of August (dekad 23) and ended on last dekad of September (dekad 27). Under ideal crop and soil condition, the longest (87 days), shortest (36 days) and mean growing period of 61 days with CV of 24.6% and SD of 15 days were observed in Kiremt. The result of analysis obtained from the Markov Chain model indicated higher probability of dry spell occurrence during Belg. In this season, the dry spell must be filled with supplementary water management system. While for Kiremt season additional rainwater harvesting mechanism needed to tight the dry spell for the month of September. Analysis of relative frequency of drought events for a given time scale revealed that mild drought occurred most frequently and extreme droughts occur with less frequency. However, when the overall drought categories (mild dry to extreme dry conditions) were considered on 12 month timescale, 79.31% and 68.97% of drought occurred during the study period in Belg and Kiremt respectively. The Mann Kendal at 5% significance level and Sequential test identified no trend and significant change in rainfall data series. Finally, the mean length of growing periods for growing sorghum and maize were 64 and 67 days with CV of 19% and 15% with SD of 12 and 10 days for Belg season while 64 and 66 days with CV and SD of 25 and 25.7% with 17 days for both crops in Kiremt season.