Summer Compound Drought-Heat Extremes Amplify Fire-Weather Risk and Burned Area beyond Historical Thresholds in Chongqing Region, Subtropical China

Abstract

Global warming is associated with an increase in compound drought-heat events (CDHEs), leading to larger and more extreme fire-weather risk in mesic forests. Wildfire activity in subtropical China, under the influence of monsoonal rainfall, was historically limited to dry winters and rare in rainy summers. Here, we seek to test whether this area is on the brink of a major change in its fire regime characterized by larger fire seasons, extending into the summer, leading to increases in fire activity (burned area). We analyze fire activity in Chongqing Municipality (46,890 km2), an important area of subtropical China hosting the Three Gorges Reservoir Area. We observed significant increases in summer forest fires under anomalous dry-hot summer conditions, where the total burned area was 3–6 times the historical annual mean (previously confined to the winter season). Vapor pressure deficit (VPD), an indicator of hot and dry weather conditions (i.e., fire-weather risk), was a strong predictor of fire activity, with larger wildfires occurring on days where VPD was higher than 3.5 kPa. Results indicate that a major wildfire activity expansion may occur in the area due to climate change and the widening time window of fire-weather risk, unless strong fire prevention and local adaptation policies are implemented.