Doubling of the population exposed to drought over South Asia: CMIP6 multi-model-based analysis.

Drought has a substantial socioeconomic impact under the changing climate. The estimation of population exposure to drought could be the pivotal signal to predict future water scarcity in the climate hotspot of South Asia. This study examines the changing population exposure to drought across South Asia using 20 climate model ensembles from the latest CMIP6 and demographic data under shared socioeconomic pathways (SSPs). Underpinning the latest version of the IPCC 6th Assessment Report (AR6), this paper focuses on the 2021-2040 (near-term), 2041-2060 (mid-term), and 2081-2100 (long-term) periods to project population exposure changes relative to the reference period (1995-2014) under four SSP-RCP scenarios. Drought events are detected by adopting the standardized precipitation evapotranspiration index (SPEI) and run theory method. Model validation suggests that CMIP6-GCM performs well in projecting climate variables and capturing drought events. The results show that the projected increases in frequent drought events and affected areal coverage are stronger during the early part of the century and weaker at the end under all scenario combinations. In relative terms, the projected increase in the number of people exposed to drought is dominant (>1.5-fold) in the near-term and mid-term periods but decreases in the long-term period. Compared to the reference period, the leading increase in population exposure (2.3-fold) is projected under the newly designed gap scenario (SSP3-7.0) in the mid-term period. A surprising decline in the number of exposed populations was estimated to be 18.8% under SSP5-8.5 by the end of the century. The mitigating effect of the predicted heavy precipitation will decrease droughts in the late future. Spatially, increasing exposure will become more pronounced across India and Afghanistan. Furthermore, the population change effect is mainly responsible for the exposure changes in South Asia. However, this study strongly recommends future 'plausible world' regional rivalry pathways (SSP3) scenario-combinations into consideration for policymaking in regard to water management as well as migration planning over South Asia.