Evaluation of the CMIP5 Climate Model for Precipitation Projections Over the Upper Blue Nile Basin

Abstract

Information on precipitation projection over a given basin is vital to determine the future climate and related water resources concerns. General Circulation Models (GCMs) are the primary tools that are used in climate change impact studies. In this study, evaluation of the new generation models from the Coupled Model Intercomparison Project phase 5 (CMIP5) was conducted for various characteristics of precipitation over the upper Blue Nile basin. This is based on over 20 GCMs and two emission scenarios from the Representative Concentration Pathways (RCP), RCP4.5 and RCP8.5. The current period 1971-2000 was compared with future projections of the period 2035-2065, representing the 2050s. The performance of GCMs to project total precipitation at different time scales as well as the frequency of occurrence are thoroughly assessed. The historical evaluation revealed most of the climate models to have a dry bias when compared with observational records. About a third of the models produced acceptable performance in terms of mean error, although there is no clear correlation with the spatial resolution or the type of climate model. Concerning the 2050s projection, a wide uncertainty range comprising both increasing and decreasing precipitation change (similar to +/- 70%) is estimated based on all GCMs while the median change shows slightly wetter condition (+3%) for this basin. This wide uncertainty indicates the need to carefully consider models when conducting impact analysis studies.