Sensitivity of modeled Indian monsoon to Chinese and Indian aerosol emissions

Peter Sherman,Jean-François Lamarque,Alex T. Archibald,Meng Gao,Drew Shindell,Gregory Faluvegi,Nathan Luke Abraham,Shaojie Song,Michael B. McElroy

doi:10.5194/acp-21-3593-2021

Abstract

Abstract. The South Asian summer monsoon supplies over 80 % of India's precipitation. Industrialization over the past few decades has resulted in severe aerosol pollution in India. Understanding monsoonal sensitivity to aerosol emissions in general circulation models (GCMs) could improve predictability of observed future precipitation changes. The aims here are (1) to assess the role of aerosols in India's monsoon precipitation and (2) to determine the roles of local and regional emissions. For (1), we study the Precipitation Driver Response Model Intercomparison Project experiments. We find that the precipitation response to changes in black carbon is highly uncertain with a large intermodel spread due in part to model differences in simulating changes in cloud vertical profiles. Effects from sulfate are clearer; increased sulfate reduces Indian precipitation, a consistency through all of the models studied here. For (2), we study bespoke simulations, with reduced Chinese and/or Indian emissions in three GCMs. A significant increase in precipitation (up to ∼20 %) is found only when both countries' sulfur emissions are regulated, which has been driven in large part by dynamic shifts in the location of convective regions in India. These changes have the potential to restore a portion of the precipitation losses induced by sulfate forcing over the last few decades.

Highlights

The South Asian summer monsoon is the dominant weather pattern over India, lasting typically from June to September
We start with an evaluation using the Precipitation Driver Response Model Intercomparison Project (PDRMIP) experiments (Table 1) of summertime Indian precipitation changes caused by large black carbon (BC) and sulfate concentration increases over all of Asia
We find a large intermodel spread in cloud profile and precipitation changes in the various BC emissions scenarios studied here

Summary

Introduction

The South Asian summer monsoon is the dominant weather pattern over India, lasting typically from June to September. Over this period, southwesterly winds transport warm, moist air from the Arabian Sea onto the Indian subcontinent, supplying roughly 80 % of the region’s annual rainfall (Turner and Annamalai, 2012). Since the monsoon provides such a significant source for India’s water supply, changes in its strength and position would have important socioeconomic implications including though not confined to agricultural production (Kumar et al, 2004; Douglas et al, 2009) and drought frequency (Subbiah, 2004). Sherman et al.: Sensitivity of modeled Indian monsoon to Chinese and Indian aerosol emissions orography of the surrounding region and difficulties in modeling intense precipitation, resolving the future roles of natural variability and the externally forced signal for the monsoon is a fundamentally difficult – but important – problem

Objectives

Results

Conclusion