Agricultural practices and water resources management in the central highlands of Ethiopia is highly dependant and associated with climatic resources and their pattern and hence wise use of those resources is a priority for the region. Accordingly, a study was conducted to asses and critically quantity the climate resources of the central high lands of Ethiop, Bishoftu district. Thirty three years of weather record data has been used for the work. The onset, duration and end of the growing seasons were defined and quantified based on FAO and Reddy models while the dry and wet spell distributions and the drought events were calculated using the Markov chain models and the standardized precipitation index (SPI) respectively. The results revealed that the mean onset of the main (Kiremt) growing season was found to occur during the second meteorological decade and ended during the end of September. Similarly, though unreliable and only few occurred during the entire study period, the mean onset of the shorter (Belg) season was found to occur during the beginning of the first decade of April. The length of the growing season during the main rainy season, (Kiremt,) ranged from 112 to 144 days with a standard deviation of 9.6 days and coefficient of variation of 7.5%. However, the mean growing length during the Belg season was found to be 22.4 days with a standard deviation of 27 days and coefficient of variation of 122%. The results of analysis obtained both from the Markov Chain and Reddy models indicated higher probabilities of dry spell occurrences during the shorter season (Belg) but the occurrences of the same in the main rainy season (Kiremt) was very minimal. Like wise, the SPI model detected some drought events ranging from mild to severe classes in both seasons based on one a month time scale analysis. A considerable attention of maximizing crop harvest during the main rainy season is practically important

Knowledge of rainfall pattern is very important for making decision on crop planning and water management. In the present study, Markov Chain probability model was performed to explain the long term frequency behavior of wet or dry weather spells during the main rainy season at Dhera, Central Rift Valley Region of Ethiopia. The study used 24 years (1984-2010) of rainfall data and weekly rainfall data was considered as standard to study the probabilities of occurrences of dry and wet weeks. Some reasonable and significant conclusions regarding specific time for land preparation, supplementary irrigation and soil conservation measures were obtained. The main rainy season starts on the 26 th week (25 th June-1 st July) and remains active upto the 40 th week (1 st-7 th October) this shows a total of 105 days of main rainy season that could occur. The coefficients of variation at the onset and withdrawal week are 69.4 and 99.2% respectively for the study site during the main rainy season. The probability of occurrences of initial and conditional probability is more than 50% on the 26 th week at 10 mm per week threshold limit and 28 th week at 20 mm per week threshold limit, therefore land preparation for planting could be undertaken in 26 th and 28 th weeks respectively for the main rainy season crop cultivation. Initial and conditional probabilities at 20 mm threshold limit per week showed that, supplementary irrigation and moisture conservation practice need to be practiced between 38 th and 40 th week for short duration crops and if the crop duration extend after 40 th week it's evident that supplementary irrigation is needed. In addition, harvesting runoff water for supplementary irrigation and construction of soil erosion measures need to be practiced between 28 th and 33 rd weeks for better rain water management.

The objective this study was to analyze the dry and wet spell of the main and small rainy season in the eastern part of Ethiopia, West Haraghe. Markov Chain model was employed to investigate the extent and characteristics of the dry and wet spell in the study sites. Accordingly, the results exhibited that the chance of having wet dekades is relatively higher (greater than 50% of probability of occurrences) during last of June to the start of October for all the study locations (Hirna, Asebe Teferi and Meios). The probability of having wet after wet is also fairly enough that farmers can take significant agricultural operations, like planting during the start of the season, second dekade of June. The probability of having wet during belg is however very low (usually less than 40%). But the soil moisture from the season could help farmers start plough earlier so that farmers can have the full advantage of the main rainy season, without wasting moisture for other activities.