Understanding Forced Asian Monsoon Changes in Observations and Coupled Model Intercomparison Project - Phase 5 (CMIP5) Models

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The Asian monsoon covers a region including India, Southeast Asia, and much of China, and is the primary source of water for a large portion of the world's population. The region also produces a large share of the anthropogenic aerosols worldwide, and several studies have suggested that aerosols, in combination with greenhouse gases and human land use and land cover (LULC) change, have a significant effect on Asian monsoon rainfall. The objective of this study is to determine the Asian monsoon response to anthropogenic forcing through the analysis of observations as well as model simulations from the Coupled Model Intercomparison Project version 5 (CMIP5). The work includes an examination of model simulations, including simulations forced by individual anthropogenic factors (for instance only aerosols or only greenhouse gas increases), to determine the relative contributions of the different human drivers of monsoon change. Further work includes simulations with two atmospheric general circulation models to test the monsoon rainfall response to factors including LULC change, and to identify the separate effect of remote sea surface temperature variations.The work has broader impacts due to the large societal impact of changes in monsoon rainfall, particularly given studies which suggest that the region could experience a substantial reduction in agricultural production by 2050 due to climate change. Work conducted here seeks to identify the underlying physical mechanisms which lead to monsoon change, and determine whether monsoon change occurring in model simulations is consistent with observational evidence. The work thus seeks to provide better guidance on likely changes in monsoon rainfall over the 21st century.