Reply on RC2

Abstract

The influence of aerosol emissions’ geographic distribution on the magnitude and spatial pattern of their precipitation impacts remains poorly understood. In this study, the NCAR CESM1 global climate model is used in coupled atmosphere-slab ocean mode to simulate the global hydrological cycle response to a fixed amount and composition of aerosol emitted from 8 key source regions. The results indicate that the location of aerosol emissions is a strong determinant of both the magnitude and spatial distribution of the hydrological response. The global-mean precipitation response to aerosol emissions is found to vary over a six-fold range depending solely on source location. Mid-latitude sources generate larger global-mean precipitation responses than do tropical and sub-tropical sources, driven largely by the formers’ stronger global-mean temperature influence. However, the spatial distribution of precipitation responses to some (largely tropical and sub-tropical) regional emissions are almost entirely localized within the source region, while responses to other (primarily mid-latitude) regional emissions are almost entirely remote. It is proposed that this diversity arises from the differing strength with which each regional emission generates fast precipitation responses that remain largely localized. The findings highlight that tropical regions are particularly susceptible to hydrological cycle change from either local or remote aerosol emissions, encourage greater investigation of the processes controlling localization of the precipitation response to regional aerosols, and demonstrate that the geographic distribution of anthropogenic aerosol emissions must be considered when estimating their hydrological impacts.