Substantial increase in the joint occurrence and human exposure of heatwave and high-PM hazards over South Asia in the mid-21st century

With daily averaged PM2.5 surface concentration of 60 μg/m3 defined as the threshold for such "unhealthy" extremes, high-PM extremes would occur 132 ± 8 days/year in the Decade 2050 under RCP8.5. Even more concerning, due to the potential health impacts of two stressors acting in tandem, is the joint occurrence of the heatwave and high-PM hazard (HHH), which would have substantial increases of 175% in frequency and 79% in duration.

This is in contrast to the 73-76% increase for heatwave or high PM when assessed individually. The fraction of land exposed to prolonged HHH increases by more than tenfold in 2050. The alarming increases in just a few decades pose great challenges to adaptation and call for more aggressive mitigation.

For example, under a lower emission pathway, the frequency of HHH will only increase by 58% with a lower frequency of high-PM extremes.