Abstract
The global monsoon is characterised by transitions between pronounced dry and wet seasons, affecting food security for two-thirds of the world’s population. Rising atmospheric CO2 influences the terrestrial hydrological cycle through climate-radiative and vegetation-physiological forcings. How these two forcings affect the seasonal intensity and characteristics of monsoonal precipitation and runoff is poorly understood. Here we use four Earth System Models to show that in a CO2-enriched climate, radiative forcing changes drive annual precipitation increases for most monsoon regions. Further, vegetation feedbacks substantially affect annual precipitation in North and South America and Australia monsoon regions. In the dry season, runoff increases over most monsoon regions, due to stomatal closure-driven evapotranspiration reductions and associated atmospheric circulation change. Our results imply that flood risks may amplify in the wet season. However, the lengthening of the monsoon rainfall season and reduced evapotranspiration will shorten the water resources scarcity period for most monsoon regions.
Highlights
The global monsoon is characterised by transitions between pronounced dry and wet seasons, affecting food security for two-thirds of the world’s population
Our analysis of expected future changes are based predominantly on results from Coupled Model Intercomparison Project phase 5 (CMIP5) Earth System Model (ESM) simulations with 1% per year increases in atmospheric CO2 concentrations, which reach a quadrupling of preindustrial levels after 140 modelled years[24]
As the total wet season precipitation is a function of the average intensity of precipitation and monsoon length, our seasonal-scale assessment includes changes to both characteristics of monsoon
Summary
The global monsoon is characterised by transitions between pronounced dry and wet seasons, affecting food security for two-thirds of the world’s population. Rising atmospheric CO2 influences the terrestrial hydrological cycle through climate-radiative and vegetationphysiological forcings How these two forcings affect the seasonal intensity and characteristics of monsoonal precipitation and runoff is poorly understood. Runoff increases over most monsoon regions, due to stomatal closure-driven evapotranspiration reductions and associated atmospheric circulation change. Stomatal closure-driven evapotranspiration reductions and associated atmospheric circulation change increase dry season runoff and shorten the water resources scarcity period for most monsoon regions. These findings highlight the importance of plant responses to rising CO2 for modulating monsoon projections and their potential buffering of global warminginduced water scarcity
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