Investigating the Factors Affecting Monsoon Precipitation Under Climate Change

Abstract:

The monsoons produce some of the largest levels of uncertainty in projected precipitation change across the globe, and addressing this uncertainty is a key issue that must be faced in order to allow for correct adaptation strategies to be put in place. A set of CMIP6 GCM experiments, that allow the full effect of CO2 forcing to be decomposed into individual components, highlight the leading factors that produce changes in monsoon precipitation (such as the direct radiative effect of increased CO2, the plant physiological effect, and the impact of uniform and patterned SST changes). The results reveal changes in the Indian Monsoon are dominated by the effect of changing SSTs and the direct radiative effect of increased CO2, and changes in the South American Monsoon are governed by the direct radiative effect and the plant physiological effect. The direct radiative effect is shown produce an increase in precipitation across almost all monsoon regions (a result consistent across a range of CMIP6 models) and further work is done to investigate the mechanism behind this projected increase, with a focus on West Africa. A set of spin-up experiments reveal that the increase in precipitation is caused by differential warming between the monsoon region and the Sahara, driving a stronger monsoon circulation.