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. 1. 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 [1–3]. This variability often translates into severe droughts and floods [4] and may substantially impact food security and water resources. Therefore, changes in future climate may pose significant threats to the region especially in resource poor contexts where agriculture is a prominent instrument for enhancing food security, and adaptive capacity is relatively low [5]. The production of accurate and reliable climate change scenarios for the West African continent is therefore a major issue. In this region, climate change projections have been often derived using global climate models (GCMs) [6, 7]. However, despite the significant progress in climate modeling, projections over West Africa are limited by at least two factors. First, the West African monsoon precipitation response to anthropogenic climate change is uncertain [8, 9] because the spread among the
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