Étude de l’influence des niveaux du réchauffement global sur les évènements extrêmes de pluie et de température en Afrique Centrale à partir du modèle COSMO-CLM

Abstract

This study assesses the performance of the regional climate model COnsortium for Small-scale MOdelling in CLimate Mode (COSMO-CLM/CCLM) by simulating the spatio-temporal characteristics of rainfall and temperature in Central Africa, and then makes a projection on the changes of these two climate parameters based on the global warming levels (GWLs) predicted over the XXIe century according to the greenhouse gas (GHG) emission scenario RCP8.5. CCLM was forced respectively by four GCMs (EC-Earth, MPI-ESM, HadGEM2 and CNRM-CM5, for the period 1950-2100) and ERA-Interim reanalysis data (ERAINT, for the period 1989-2008), at 50 km horizontal resolution grid. During the validation period (1989-2008), we first evaluated the ability of CCLM (forced by ERAINT) to represent the climatology of precipitation and temperature in CA, before estimating the ability of CCLM (forced by GCMs) to reproduce nine (09) hydro-climatic indices based on daily precipitation (06) and temperature (03). An emphasis was placed on the added value at the local scale. We found that, on the CA, CCLM model reasonably reproduces the mean spatial distributions and mean seasonal cycles of precipitation and temperature, as well as the associated low-level circulation characteristics. The results also show that the precipitation and temperature indices are satisfactorily represented, although good performance depends largely on indices and seasons considered. In addition, CCLM provides notable improvements to the ERAINT reanalyses and GCMs, highlighting the added value of the downscaling exercise. Analysis of climate change signals for the 21st century has shown that a gradual increase in GWLs (from 1.5-3.0 ◦C) will create over the CA, a generalized decrease in precipitation (up to 50 %), and an increase in surface temperatures (up to 18 %). We found that the future decrease in precipitation is likely due to a decrease in the number of wet days with wet spells, combined to an increase in dry spells. On the other hand, the increase in future temperatures is associated with the increase in extreme temperatures.