Spatio-temporal hydro-climate variability in Omo-Gibe river Basin, Ethiopia

Hydroclimatic variables have changed globally mainly due to human intervention; those hydroclimatic changes alter the distribution behavior of rainfall and temperature at different scales. This study examined the magnitude of temporal and spatial variation of hydroclimatic variables in the Omo-Gibe River Basin (OGRB) using rainfall and temperature data from 1981 to 2016 and river flow data from 1981 to 2014. Mann-Kendall and Sen's slope estimator trend test were used to analyze the distribution and trends of rainfall, temperature, surface runoff, and river flow. The result shows rainfall variability has been higher in the northern and central parts and decreasing towards the southern part of the OGRB to its southern part. Results also show that seasonal and annual mean temperatures have increased significantly in the recent two decades. The northern and central OGRB summer and autumn seasons' rainfall shows a statically insignificant positive trend. However, the basin has been experiencing less to high spatio-temporal seasonal and monthly rainfall variability. Runoff and flow of the basin were constant in all rivers during the period 1981 to 1997. However, the basin experienced peaks and diminished runoff and flowed, particularly in the recent two decades. The mean seasonal trend of runoff increased insignificantly, whereas the river flow increased significantly during the summer, spring, and autumn seasons by 0.069, 0.014 and 0.197 m(3)s(-1)/year, respectively. Overall, the mean annual runoff and river flow observed an insignificant increasing trend in the entire basin. In general, the erraticity of rainfall, rising temperature, and the highest spatial and temporal variation of river flow and runoff witnessed in OGRB suggest that the basin water resource is at risk due to these reinforcing challenges, and much needs to be done by all the concerned actors to save water resources.