Escalating Hot-Dry Extremes Amplify Compound Fire Weather Risk

Fire weather compounded by extremely hot and dry conditions often severely impacts society and ecosystems. To mitigate and better adapt to these compound fire weather (CFW) events, a better understanding of recent and future CFW trends is needed. Here we show that in the period 1981-2020, the global average frequency and intensity of CFW events increased by 0.6 days/yr and 0.4%/yr, respectively. Increases in temperature and decreases in relative humidity were responsible for significant trends in the frequency of CFW events in 81.7% and 58.6% of locations, respectively. The same trends contributed to significant increases in CFW intensity in 72.1% and 57.9% of locations. We further demonstrate that anthropogenic climate change (due primarily to greenhouse gas emissions) has aggravated the frequency and intensity of CFW events, particularly in the Amazon region, with over 2-fold and 1.3-fold increases, respectively. Future projections reveal that other (individual) fire weather events are likely to shift toward CFW events accompanied by hot-dry conditions, along with an expected rise in CFW intensity. Furthermore, the increased occurrence of CFW events is likely to substantially augment future population exposure to CFW conditions. Under the SSP5-8.5 scenario, climate change is estimated to contribute 62.6% of the projected increase in population exposure to CFW events by the end of this century. Our findings underscore the urgent need for strong climate action to reduce population exposure to the growing threat of future fire weather events compounded with hot and dry conditions.