The Impact of Rainfall Variability and Crop Production on Vertisols in the Central Highlands of Ethiopia

Abstract

Abstract Understanding the yearly, seasonal, monthly, and weekly rainfall variability is crucial for improved agricultural practice in a country like Ethiopia, where agriculture depends on rainfall. In particular, knowledge of rainfall onset, withdrawal, amount, distribution, and the length of the crop growing period would protect farmers from crop damage due to climatic anomalies. This study collected and described thirty-nine years of rainfall data using the Markov chain model. Based on the rainfall probability levels at different threshold levels, the length of the dry and wet spells and the length of the growing period were determined. The study shows dependable rainfall at a 75% probability level commences in June. The chance of receiving greater than 10 mm at a 50% probability level starts in week 10 (5 March–11 March), with much discontinuity up to week 21st (21 May–27 May). The dependable weekly rainfall begins the week of 22 May (28th May-3rd June) with a probability of greater than 20 mm. The study revealed that the short rainy season rainfall (February to May) is unreliable for growing crops at Ghinchi as opposed to other highland areas of Ethiopia. The length of the growing season is therefore confined to periods of the long rainy season (weeks 22nd to 39th, or 28th May-30th September). The water balance for the study area indicates that the moisture availability index is greater than 0.5,and potential evapotranspiration is lower than precipitation during these months.