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Uncertainty in the projected changes of Sahel summer rainfall under global warming in CMIP5 and CMIP6 multi-model ensembles

Abstract

The Sahel summer rainfall is of great significance to the local social, economic, and cultural environment. In the context of a long Sahel megadrought in the last thirty years of the twentieth century, the future change of Sahel summer rainfall under global warming has aroused wide attention. Based on the historical simulations and high emission scenario experiments from 20 Coupled Model Intercomparison Project phase-5 (CMIP5) models and 22 CMIP6 models, this study investigates the future projections of Sahel summer rainfall under global warming. The results show that the multi-model ensemble (MME) mean projects a slight increase (1–2%/℃) of summer rainfall over the Sahel in the future which seems to be due to the thermodynamic changes and opposed by the dynamic changes, but that the inter-model spread is due to the latter. We find that, in particular, the inter-model spreads in the extratropical northern and tropical Atlantic sea surface temperature (SST) changes are two important sources of the uncertainty in the Sahel summer rainfall projections via two different atmospheric teleconnection processes. On the one hand, a warmer northern Atlantic SST would induce an anomalous large-scale cyclone over North Africa and Europe, and the southern branch would strengthen the western African monsoonal circulation, leading to a wetter Sahel. On the other hand, a warmer tropical Atlantic SST would weaken the regional circulation, resulting in a drier Sahel. Our results suggest that an improved projection of the future Atlantic warming, especially the differential warming between the northern and tropical Atlantic, is a priority for the reliable future projection of Sahel summer rainfall.

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Data Availability Statement

The data used in the present study are downloaded from the following websites: CMIP5 models’ outputs: https://pcmdi.llnl.gov/mips/cmip5/. CMIP6 models’ outputs: https://pcmdi.llnl.gov/CMIP6/. Reanalyzed monthly rainfall: https://crudata.uea.ac.uk/cru/data/hrg/cru_ts_4.02/. Reanalyzed monthly wind:https://psl.noaa.gov/data/gridded/data.20thC_ReanV2c.html.

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Acknowledgements

This work is supported by the Natural Science Foundation of China (41831175), the Fundamental Research Funds for the Central Universities (B200202138 and B210201015), and the Open Research Fund of the State Key Laboratory of Loess and Quaternary Geology of China (SKLLQG1939). We acknowledge the climate modeling groups (Table 1) for producing and making available their model output, the U.S. Department of Energy’s Program for Climate Model Diagnostics and Inter-comparison for providing coordinating support and leading development of software infrastructure in partnership with the Global Organization for Earth System Science Portals, the World Climate Research Programme’s Working Group on Coupled Modelling which is responsible for CMIP, the NOAA/OAR/ESRL PSL, Boulder, Colorado USA for providing the wind data (https://psl.noaa.gov/data/gridded/data.20thC_ReanV2c.html), and the Climatic Research Unit, University of East Anglia for providing the rainfall data (https://crudata.uea.ac.uk/cru/data/hrg/cru_ts_4.02/).

Funding

This project was supported by the Natural Science Foundation of China (41831175), the Fundamental Research Funds for the Central Universities (B200202138 and B210201015), and the Open Research Fund of the State Key Laboratory of Loess and Quaternary Geology of China (SKLLQG1939).

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Zhang, Z., Li, G. Uncertainty in the projected changes of Sahel summer rainfall under global warming in CMIP5 and CMIP6 multi-model ensembles. Clim Dyn (2022). https://doi.org/10.1007/s00382-022-06284-3

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Keywords

  • Sahel summer rainfall
  • Future projection
  • Inter-model uncertainty
  • Global warming
  • Atlantic Ocean warming
  • Atmospheric teleconnection