Dipole in Future Anthropogenic Emission Scenarios Across India and China Strongly Influences Spatial Distribution of Monsoon Rainfall Response

A recent study by Samset et al. (2019) has shown that future near-term Shared Socioeconomic Pathways (SSPs) in India and China may result in a range of aerosol emission patterns, including a continuation of the strong dipole pattern observed since 2010. Anthropogenic aerosol emissions from India and China impact Asian summer monsoon rainfall through modifications to the surface energy balance, the boundary layer temperature profile, and the large-scale atmospheric circulation. All aerosol species act to cool the surface, but absorbing species such as black carbon also produce localised heating aloft which can cause distinct regional and large-scale circulation changes. We investigate the impact of the aerosol emission dipole on the Asian summer monsoon using an intermediate General Circulation Model with observationally constrained aerosol profiles over India and China.

By isolating the emissions from both countries, we provide new insight into how the range of aerosol emission scenarios in the SSPs might influence monsoon rainfall. A reduction in absorbing aerosol emissions from China alone strongly increases monsoon rainfall throughout China whilst reducing Indian rainfall, whereas a reduction in absorbing aerosol emissions from both countries shifts Indian rainfall to the north of the country whilst increasing rainfall across China. These simulations highlight that anthropogenic aerosol scenario uncertainty is likely to compound the already large uncertainty in projected monsoon changes, and that the climate and health impacts of air quality policy need to be considered together for effective adaptation.

Samset, B., Lund, M., Bollasina, M., Myhre, G., Wilcox, L. "Emerging Asian aerosol patterns", Nature Geoscience, https://doi.org/10.1038/s41561-019-0424-5, 2019