Jiang, Xiaoyan, Mary C. Barth, Alex E. Guenther,
Louisa Emmons, and Christine Wiedinmyer, National Center for Atmospheric
Research, USA
Anthropogenically-induced
land-use/land cover change has been identified as a significant forcing that
can impact Asian monsoon precipitation characteristics through altering the
surface Bowen ratio, boundary layer processes, and land–atmosphere coupling.
Aerosols, in particular those related to anthropogenic activities, including
black carbon, organic carbon, and sulfate aerosols, have been found to affect
the Asian monsoon through direct and indirect aerosol radiative forcing. In
this work, we use the coupled regional Weather Research and Forecasting model
with Chemistry (WRF-Chem) to understand and compare how these changes caused by
human activities could modulate the Asian monsoon system (i.e., monsoon
development and evolution). A series of 6-month WRF-Chem sensitivity
experiments have been carried out, and the modeling results are evaluated
against reanalysis data and satellite observations. When considering the
aerosol radiative forcing, in particular the indirect radiative forcing, the
model performs well in simulating monsoon season rainfall over India, East
China, and some regions in South Asia where the air is heavily polluted. The
impacts on precipitation due to land use change are smaller as compared to the
impacts of aerosols. Detailed analysis regarding the changes in radiation,
surface fluxes, atmospheric heating, and circulation patterns due to land-use
change and aerosols are presented to further explain the roles of short-lived
air pollutants versus land-use change in the Asian monsoon system.