Human influence strengthens the contrast between tropical wet and dry regions

Schurer, Andrew P., Ballinger, Andrew P., Friedman, Andrew R. and Hegerl, Gabriele C. (2020) Human influence strengthens the contrast between tropical wet and dry regions. Environmental Research Letters, 15 (10). ISSN 1748-9326

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Abstract

Climate models predict a strengthening contrast between wet and dry regions in the tropics and subtropics (30 °S–30 °N), and data from the latest model intercomparison project (CMIP6) support this expectation. Rainfall in ascending regions increases, and in descending regions decreases in climate models, reanalyses, and observational data. This strengthening contrast can be captured by tracking the rainfall change each month in the wettest and driest third of the tropics and subtropics combined. Since wet and dry regions are selected individually every month for each model ensemble member, and the observations, this analysis is largely unaffected by biases in location of precipitation features. Blended satellite and in situ data from 1988–2019 support the CMIP6-model-simulated tendency of sharpening contrasts between wet and dry regions, with rainfall in wet regions increasing substantially opposed by a slight decrease in dry regions. We detect the effect of external forcings on tropical and subtropical observed precipitation in wet and dry regions combined, and attribute this change for the first time to anthropogenic and natural forcings separately. Our results show that most of the observed change has been caused by increasing greenhouse gases. Natural forcings also contribute, following the drop in wet-region precipitation after the 1991 eruption of Mount Pinatubo, while anthropogenic aerosol effects show only weak trends in tropic-wide wet and dry regions consistent with flat global aerosol forcing over the analysis period. The observed response to external forcing is significantly larger (p > 0.95) than the multi-model mean simulated response. As expected from climate models, the observed signal strengthens further when focusing on the wet tail of spatial distributions in both models and data.

Item Type:	Article
Additional Information:	Data statement Data used in this study is publicly available from the following sources: CMIP model output is available at: http://pcmdi9. llnl.gov/. The GPCP and CMAP data were provided by the NOAA Office of Oceanic and Atmospheric Research (OAR) Earth System Research Laboratory (ESRL) Physical Sciences Division (PSD). The ERA5 output (downloaded at 0.25° x 0.25° resolution for precipit-ation and 2.5° x 2.5° for other variables) is available from the Copernicus Climate Change Service (C3S) Climate Data Store. The MERRA-2 output (down-loaded at 2.5° x 2.5° resolution) is available from the Goddard Earth Sciences Data and Information Services Center. The JRA-55 output (downloaded at 1.25° x 1.25° resolution) was provided via the JMA Data Dissemination System (JDDS). All analysis code will be made available on request.
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	LivePure Connector
Date Deposited:	23 Dec 2025 16:30
Last Modified:	23 Dec 2025 20:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101504
DOI:	10.1088/1748-9326/ab83ab

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