Variability and trend analysis of rainfall and temperature in the Genale Dawa River Basin, Ethiopia

Since the Genale Dawa River Basin has significant irrigation potential, a new project has been started to encourage irrigation extension. Nevertheless, these initiatives need accurate, site-specific data on past temperature and precipitation, two essential elements of climate variables. However, there is a lack of comprehensive site-specific information on these variables in the river basin. The main objective of this study was to investigate temperature and rainfall trends and variability during the past 30 years (1984–2014) at 15 selected stations. Accordingly, the observed historical rainfall data were assessed for the Coefficient of Variation (CV) and Precipitation Concentration Index (PCI). The trend and magnitude of change in rainfall and temperature were tested through the Mann-Kendall test and the Sen’s slope estimator, respectively. The results showed that the annual rainfall coefficient of variation is between 12.9% and 38.57%. The aggregate result of the stations’ Precipitation Concentration Index indicated that low concentration (5.1%), moderate concentration (45.3%), strong concentration (24.9%), and strong irregularity (24.7%) indicated spatial variability of precipitation. Annual and seasonal maximum and minimum temperatures have resulted in an increasing trend at all the stations. Generally, there was a spatially and temporally variable trend in rainfall, while the temperature trend was increasing irrespective of the temporal and spatial factors that have far-reaching consequences on the availability of water resources in the area, which requires the development of effective climate variability mitigation and adaptation measures in the study area.