Future Amplification of Multivariate Risk of Compound Drought and Heatwave Events on South Asian Population

Over the past few decades, South Asia (SA) has experienced an upsurge in the frequency of severe monsoonal compound drought and heatwave (CDHW) occurrences. Climate models that identify land-atmosphere coupling as a major contributing factor for this exacerbation and anticipate an increase in the intensity and frequency of CDHW occurrences in future also represent this. For the first time, this study investigated the future evolution of monsoonal CDHW events based on new generations of the CMIP6 and population products by applying a multivariate framework. Specifically, this study explored the impacts of natural climate variability and future land-atmosphere coupling on the monsoonal CDHW event risks and their bivariate return periods for two future time-periods and emission scenarios across SA and its subregions. The odds of CDHW occurrences were then examined using a logistic regression model and its association with the natural and anthropogenic drivers was determined. The results indicate that the monsoonal CDHWs occurrence is anticipated to increase substantially during the late twenty-first century (2056-2090). The 50-year CDHW events might increase by two-fold across most of SA by the mid-21st century under the high emission scenario. We find that the co-occurring dry and warm conditions rapidly strengthens with soil moisture and temperature coupling and are further exacerbated by land-atmospheric feedback loops. Our findings show that persistent dry spells contribute significantly to heatwave events, emphasizing regional exposure to changing climates. CDHW (compound drought and heatwave) events may have caused more severe effects on agriculture, water resources, and human society than their occurrences. Investigating future changes in CDHW is critical for anticipating and reducing the adverse effects of climate change and variability, especially in a densely populated region like South Asia (SA), where most of the population still depends on agricultural productivity. Here, we propose a novel compound and multivariate risk assessment framework to capture weekly droughts and heatwaves at a daily time scale using advanced scientific methods. With this objective, the outcomes of the current study can directly map the vulnerable areas in SA and expose the relationship between two events (drought and heatwave). The current research also explores the risk and population exposure due to CDHW events across SA under current and future warming climates by considering the joint distribution of CDHW severity and duration. The study findings will help inform stakeholders about vulnerable areas where the CDHW events are more likely to become more frequent and severe due to climate change. CDHW occurrences are projected to increase significantly during the period mid and late 21st century under the business-as-usual scenarioThe population exposure from 50-year CDHW event might increase two-fold across 70% of the SA landmasses already by the mid-21st centuryAnthropogenic global warming show significant positive influence on the most vulnerable climatic regions