Spatial and Temporal Uncertainty of Rainfall in Arid and Semi-Arid Areas of Ethiopia

Abstract

The aim of this study was to assess rainfall uncertainty and trends in the arid and semi-arid areas of Ethiopia by using rainfall data records from the thirteen stations over the period of 1952-2012. In this study annual and seasonal rainfalls were analyzed for trends, least square regression was used to quantify the trends and Spearman’s rho was used to test statistical significance of the trends. The results of the analysis in rainfall variability shows negative trend in Bulen and Asosa stations in the western arid and semi-arid areas was statistically significant at 0.71 and 0.3 levels  respectively. In the same way, inter annual seasonal rainfall shows during observation negative trends for eight to eleven stations, though not  statistically significant in most of the stations. Indeed, mean annual   rainfall in arid and semi-arid is highly seasonal and analysis of seasonal rainfall indicates a significant increase in the variability. To this effect, seasonal rainfall variability was higher during Spring and Autumn seasons in the Western stations than East and South Eastern stations. On the other hand, during observation, summer rainfall variability which directly affecting
agricultural production is less variable over western stations than East and South Eastern stations in arid and semiarid areas. The finding of the study revealed that there are significant spatial differences in mean annual, seasonal and trends of rainfall between the Western and Eastern, South Eastern arid and semiarid areas of Ethiopia.