Abstract
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 26th week (25th June - 1st July) and remains active upto the 40th week (1st - 7th 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 26th week at 10 mm per week threshold limit and 28th week at 20 mm per week threshold limit, therefore land preparation for planting could be undertaken in 26th and 28th 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 38th and 40th week for short duration crops and if the crop duration extend after 40th 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 28th and 33rd weeks for better rain water management. Key words: Markov chain model, onset week, withdrawal week, agricultural planning.
Highlights
Ethiopian farming is mainly dependant on rainfed smallholder agricultural system as a means of food and income for its population (Hordofa et al, 2008)
34.00 preceded by wet week is calculated by subtracting probability of a dry week preceded by dry week and probability of a wet week preceded by a wet week from 100
At 20 mm per week threshold limit, the conditional probability of wet week (Pww) during the main rainy season is more than 50% with a value of
Summary
Ethiopian farming is mainly dependant on rainfed smallholder agricultural system as a means of food and income for its population (Hordofa et al, 2008). Agricultural production from rainfed agricultural system depends on all climatic parameters, rainfall is the most important and sensitive one Both shortage and surplus of rainfall during the length of the crop growing period can lead to full or partial crop failure. Production can be increased and risk minimized by selecting the right time for the onset of rainfall based on informed decision by analyzing the long term rainfall pattern and variability as well as harvesting excess water and utilizing it in periods of shortage as supplementary irrigation. Farmers usually made traditional crop planning decision based on the onset of rainfall for Belg season (small amount of rain before the main rainy season). This study has been carried out to determine the onset and withdrawal of rainy season, probabilities of occurrences of onset and withdrawal of rainy seasons and the initial and conditional probabilities of dry and wet weeks using threshold limits of 10 mm and 20 mm of rainfall during the main rainy season at Dodota area, Central Region of Ethiopia
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