Evaluation of present-climate precipitation in 25 km resolution regional climate model simulations over Northwest Africa

Abstract

Risks related to characteristics of future precipitation change over northern Africa (decreasing mean precipitation, floods and droughts) have been highlighted by several authors, but the scarcity of studies in this area of Africa has been noted by IPCC. We analysed the northwestern African domain for present-day climate (1989 to 2008) precipitation features from a set of 5 high-resolution (25 km) regional climate models (RCMs) from the Spanish ESCENA project. The evaluation of present-climate RCMs simulations was done by comparing the results with 4 different observational databases. The analysis of the spatial distribution of mean precipitation and the annual cycle revealed a complex spatial distribution of rainfall depending on area; hence, a more specific analysis subdividing the domain into 8 subregions was conducted. The spatial and temporal heterogeneity of the precipitation pattern in the studied domain is exemplified by the extreme events (heavy precipitation days oscillated between 4 and 16 d yr-1 and consecutive dry days between 240 and 330 d) and annual anomalies analyses (values between -50% and +100%). The study reveals many robust precipitation features over the region, but also significant differences between the models, with a spread larger than 70% in some subregions, pointing to the need for a set of RCMs and the importance of high resolution in a very complex domain. As regional models are able to describe the basic precipitation features over the region, they can be used to assess the changes projected by climate change simulations.