Reliability of NASA NEX-GDDP Dataset in Reproducing Climatological Mean Temperature and Precipitation over the Gibe III Watershed, Omo-Gibe Basin, Ethiopia

Background: The challenge of climate variability is a major problem for developing and using water resources. Scarcity of climate data compounds the problem and undermines the efforts to acquire updated information for predicting climate change and reduce its risks. Objective: The objective of the study was to evaluate and select the best climate models having NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) dataset for Gibe III watershed. Material and Methods: NEX-GDDP data of precipitation and temperature with spatial resolution of 0.25º x 0.25º of ten CMIP5 models was, evaluated against observed data of eight stations distributed in the Watershed. Results: The models showed a consistent and reasonable pattern for mean monthly total precipitation and mean temperature (max and min). The mean monthly precipitation of all models against observation also resulted to R2 of 0.71 to 0.99 and the Nash–Sutcliffe efficiency (NSE) value of 0.66 to 0.99. Mean annual precipitation of model ensemble mean over the watershed against observation spatially varied between –100 and 100 mm underestimating at the northern and southern tips of watershed while overestimating at central and northeastern parts. The mean maximum and minimum temperature varied from –1.6 ºC to +2.9 ºC and 0.4 ºC to 3.8 ºC, respectively.Conclusion: The result indicates that, selecting climate models’ ensemble mean could provide higher confidence in climate change projection than choosing a specific model for an entire watershed. Based on evaluation metrics and long-term mean annual rainfall, NEX-GDDP dataset of CSIRO-MK3-6-0, MIROC5, MPI-ESM-MR, NorESM1-M, MIROC5 and GFDL-ESM2M models reasonably simulated the mean annual rainfall at Shebe, Sodo, Jimma, Hosaina, Sokoru and Woliso stations respectively for uses of climate change projection in the Watershed. The reliability of NEX-GDDP dataset for the climate models need seasonal basis study in the future at the Watershed since this study did not conduct seasonal data analysis.