Future Projections of Extreme Integrated Water Vapor Transport and Population Exposure Over the Asian Monsoon Region

Global warming leads to an intensification of the water cycle and an increase in extreme climate events. Most previous researchers have used precipitation to project extreme hydrological changes. However, compared with precipitation, global climate models (GCMs) have a better performance in simulating the integrated vapor transport (IVT). IVT is thus a reliable tool for understanding how hydrological extremes may change in the future. In this study, we first discuss the relationship between IVT and precipitation over the Asian monsoon (AM) region during 1979-2014. We then assess the climatology, variability and extremes of IVT over the AM region and subregions using 16 GCMs from CMIP6. We further apply GCMs to project changes in the magnitude and probability of dangerous extreme IVT events (e.g., 20-, 50- and 100-year events) in the future. Finally, we quantify the population exposure to extreme IVT events, and explain change in exposure and its uncertainty. Results show that CMIP6 GCMs capture the spatial distribution of IVT well; the intensity of simulated IVT is lower than the ERA5 IVT. Under global warming of 1.5, 2, and 3 degrees C, the magnitude of extreme events, which is independent of the return period (RP), increases over the AM region with relative changes of about 7%, 12%, and 21%, respectively. The probability increases consistently with global warming and the RP. The increase in exposure for the South Asian monsoon (East Asian monsoon) region is both contributed by more extreme IVT events and higher (fewer) population counts; the former has a larger proportion.