Future evolution of the Sahel precipitation zonal contrast in CESM1
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Future evolution of the Sahel precipitation zonal contrast in CESM1 Paul‑Arthur Monerie1 · Emilia Sanchez‑Gomez2 · Marco Gaetani3 · Elsa Mohino4 · Buwen Dong1 Received: 13 February 2020 / Accepted: 7 August 2020 © The Author(s) 2020
Abstract The main focus of this study is the zonal contrast of the Sahel precipitation shown in the CMIP5 climate projections: precipitation decreases over the western Sahel (i.e., Senegal and western Mali) and increases over the central Sahel (i.e., eastern Mali, Burkina Faso and Niger). This zonal contrast in future precipitation change is a robust model response to climate change but suffers from a lack of an explanation. To this aim, we study the impact of current and future climate change on Sahel precipitation by using the Large Ensemble of the Community Earth System Model version 1 (CESM1). In CESM1, global warming leads to a strengthening of the zonal contrast, as shown by the difference between the 2060–2099 period (under a high emission scenario) and the 1960–1999 period (under the historical forcing). The zonal contrast is associated with dynamic shifts in the atmospheric circulation. We show that, in absence of a forced response, that is, when only accounting for internal climate variability, the zonal contrast is associated with the Pacific and the tropical Atlantic oceans variability. However, future patterns in sea surface temperature (SST) anomalies are not necessary to explaining the projected strengthening of the zonal contrast. The mechanisms underlying the simulated changes are elucidated by analysing a set of CMIP5 idealised simulations. We show the increase in precipitation over the central Sahel to be mostly associated with the surface warming over northern Africa, which favour the displacement of the monsoon cell northwards. Over the western Sahel, the decrease in Sahel precipitation is associated with a southward shift of the monsoon circulation, and is mostly due to the warming of the SST. These two mechanisms allow explaining the zonal contrast in precipitation change. Keywords Sahel zonal contrast · Sahel precipitation · Climate change · Internal climate variability · Large ensemble
1 Introduction The third and fifth phases of the Climate Model Intercomparison Projects (CMIP; see Taylor et al. 2012) have allowed the analysis of a large variety of climate simulations. Results have highlighted that the impact of climate change on Sahel Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05417-w) contains supplementary material, which is available to authorized users. * Paul‑Arthur Monerie [email protected] 1
National Centre for Atmospheric Science (NCAS), Department of Meteorology, University of Reading, Reading, UK
2
CECI, UMR 5318, CERFACS/CNRS, Toulouse, France
3
Scuola Universitaria Superiore IUSS, Pavia, Italy
4
Dpto. Física de la Tierra y Astrofísica, Facultad Ciencias Físicas, Universidad Complutense de Madrid, Ciudad Universitaria, Plaza Ciencias, 28040 Madrid, Spain
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