Absorbing aerosols and high‐temperature extremes in India: A general circulation modelling study

Abstract

AbstractHeat waves in India during the pre‐monsoon months have significant impacts on human health, productivity and mortality. While greenhouse gas‐induced global warming is believed to accentuate high temperature extremes, anthropogenic aerosols predominantly constituted by radiation‐scattering sulfate are believed to cause an overall cooling in most world regions. However, the Indian region is marked by an abundance of absorbing aerosols, such as black carbon (BC) and dust. The goal of this work was to understand the association between aerosols, particularly those that are absorbing in nature, and high‐temperature extremes in north‐central India during the pre‐monsoon season. We use 30‐year simulations from a chemistry‐coupled atmosphere‐only general circulation model (GCM), ECHAM6‐HAM2, forced with evolving aerosol emissions in an interactive aerosol module, along with observed evolving SSTs. A composite of high‐temperature extremes in the model simulations, compared to climatology, shows large‐scale conditions conducive to heat waves. Importantly, it reveals concurrent positive anomalies of BC and dust aerosol optical depths. Changes in near‐surface properties include a reduction in single scattering albedo (implying greater absorption) and enhancement in short‐wave heating rate, compared to climatological conditions. Alterations in surface energy balance include reduced latent heat flux, but increased sensible heat flux, consistent with enhanced temperatures. Thus, chemistry‐coupled GCM simulations capture an association of absorbing aerosols with high‐temperature extremes in north India, arising from radiative heating in the surface layer.