Multimodel GCM-RCM Ensemble-Based Projections of Temperature and Precipitation over West Africa for the Early 21st Century

I Diallo,M Camara,M B Sylla,A T Gaye,F Giorgi

doi:10.1155/2012/972896

Abstract

Reliable climate change scenarios are critical for West Africa, whose economy relies mostly on agriculture and, in this regard, multimodel ensembles are believed to provide the most robust climate change information. Toward this end, we analyze and intercompare the performance of a set of four regional climate models (RCMs) driven by two global climate models (GCMs) (for a total of 4 different GCM-RCM pairs) in simulating present day and future climate over West Africa. The results show that the individual RCM members as well as their ensemble employing the same driving fields exhibit different biases and show mixed results in terms of outperforming the GCM simulation of seasonal temperature and precipitation, indicating a substantial sensitivity of RCMs to regional and local processes. These biases are reduced and GCM simulations improved upon by averaging all four RCM simulations, suggesting that multi-model RCM ensembles based on different driving GCMs help to compensate systematic errors from both the nested and the driving models. This confirms the importance of the multi-model approach for improving robustness of climate change projections. Illustrative examples of such ensemble reveal that the western Sahel undergoes substantial drying in future climate projections mostly due to a decrease in peak monsoon rainfall.

Highlights

Addressing climate change over West Africa is a great challenge for understanding the effects of greenhouse gas (GHG) warming at local and regional scales
The June–September (JJAS) seasonal mean temperature distribution during the present-day period (1981–2000) over West Africa is presented at Figures 2(a)–2(l) for the observation of CRU (Figure 2(a)), the ERA40, NCEP, and ERA-Interim reanalyses (Figures 2(b), 2(c), and 2(d), resp.), the two global climate models (GCMs) ECHAM5 and HadCM3 (Figures 2(e) and 2(i), resp.), the two regional climate models (RCMs) RegCM3 and REMO driven by ECHAM5 (Figures 2(f) and 2(g), resp.), the two RCMs: RCA and HadRM3P (Figures 2(j) and 2(k), resp.) driven by HadCM3 and their different ensemble mean (Figures 2(h) and 2(l))
The ensemble mean of RCMs driven by ECHAM5 outperforms the individual RCMs and the GCM simulations, while the ensemble of RCMs driven by HadCM3 fails to do that

Summary

Introduction

Addressing climate change over West Africa is a great challenge for understanding the effects of greenhouse gas (GHG) warming at local and regional scales. Such assessment is critical because Africa is mostly covered by semiarid regions known for their unreliable rainfall regime which is highly variable on intraseasonal, interannual and interdecadal time scales [1,2,3]. The production of accurate and reliable climate change scenarios for the West African continent is a major issue In this region, climate change projections have been often derived using global climate models (GCMs) [6, 7]. The typical grid box of GCMs (in the range of 100–400 km) is not suitable to account for land surface heterogeneity such as vegetation variations, complex topography, and coastlines, which are important aspects of the physical response governing the local and regional climate change signal [12, 13]

Objectives

Results

Conclusion