Increasing risk of global compound humid heatwaves and the impacts of antecedent precipitation

Extreme humid heatwaves (HS) have emerged as one of the most threatening compound disasters under climate change, posing severe risks to human health and socio-economic security. Yet their dynamic evolution and mechanism, especially the relation with antecedent precipitation, remain insufficiently understood. Based on global reanalysis data from 1985 to 2024, this study presents a systematical assessment for the spatiotemporal evolution of humid heatwaves, their thermodynamic drivers, and the modulation effects of preceding precipitation. Results reveal a significant intensification trend in HS frequency, duration, and intensity, which can be statistically significantly attributed to anthropogenic forcing. The occurrences of extreme humid heatwaves are mainly driven by humidity anomaly in 94.45% of global land areas, while the influences of temperature and humidity changes on HS trends exhibit larger spatial heterogeneity. The relations between antecedent precipitation and subsequent HS are strengthening, evidenced by their increasing synchrony and high HS triggering probability. Moreover, HS exhibit distinct patterns based on preceding precipitation: HS following light precipitation are most frequent, while long-duration or heavy precipitation are likely to trigger most intense HS. Notably, HS tends to occur more rapidly after the cessation of long-duration heavy rainfall, demonstrating a differentiated regulatory mechanism from land-atmospheric coupling and necessitating context-specific adaptation strategies tailored to these divergent precipitation-HS relationships.