ANALYSIS OF CLIMATE EXTREMES OVER WEST AFRICA USING COORDINATED REGIONAL DOWNSCALING EXPERIMENT DATASETS

Abstract

The Global Climate Model (GCM) often does not successfully simulate extreme climate events due to its low spatial resolution. Meanwhile, Regional Climate Models (RCMs) at higher spatial resolution are more realistic in replicating physical processes at regional scale. In this study, a comprehensive combined analysis of extreme climate over West Africa using Co-ordinated Regional Downscaling Experiment (CORDEX)-Africa datasets is presented. The study assessed the spatio-temporal variability of West African climate; changes in climate extremes using different climate indices; and projection of future climate extreme indices by RCMs participating in CORDEX-Africa. The observed data used were the daily Tropical Rainfall Measuring Mission (TRMM) for precipitation available from 1998 to 2005 and ERA Interim for minimum and maximum temperature from 1975 to 2005. The experimental data used were the daily simulations of Community Climate Limited-area Models (CCLM4.8) and Swedish Meteorological and Hydrological Institute (SMHI-RCA) which were driven by two Global Climate Models (GCMs), Met-Office Hadley Centre (MOHC) and Max Planck Institute (MPI). The future projection datasets were based on the Representative Concentration Pathways (RCP 4.5) scenarios. The long-term mean and annual cycle of precipitation and temperatures were examined. The performances of RCMs in estimating future extreme climate were also evaluated using error metrics such as correlation coefficient (r), root mean square error (RMSE), mean bias (MB), and coefficient of efficiency (COE). The performance evaluation showed that, all CORDEX RCMs had poor correlations of less than 0.5 with the observed with minimum errors and maximum correlations. However, MOHC CCLM and MPI CCLM have been identified as the best performed models when compared with the observed. Results of both the historical and future extreme climate regimes as quantified by the Expert Team on Climate Change Detection Monitoring Indices (ETCCDMI), 3 Consecutive Dry Days (CDD), Consecutive Wet Days (CWD), Very heavy precipitation (R20mm) days, Simple Daily Intensity Index (SDII), Heat Wave Duration Index (HWDI), percentage frequency of warm days (Tx90p), percentage frequency of warm nights (Tn90p), Cold Wave Duration Index (CWDI), percentage frequency of cold days (Tx10p), and percentage frequency of cold nights (Tn10p) over West Africa showed continuous and extreme dryness in the Sahara and wetness in the coastal regions of West Africa based on the estimated extreme precipitation indices. Near surface warming was also found over the entire West African domain during the periods of study. The study suggests that, to cope with increases in extreme climate events, serious reductions in greenhouse gas emissions through policy interventions and planning must be undertaken to reduce the extent of future impacts over West Africa.