Seasonal divergence in compound heatwave–extreme precipitation events

Compound heatwave – extreme precipitation (CHWEP) events pose escalating risks in monsoon-influenced mid-latitude region across the globe, yet, long-term and seasonally-resolved observational evidence remains limited. Here, we quantify the seasonal and long-term changes, and recent shifts of CHWEP events across South Korea using daily ground observations over four decades (1986–2025). We find that the recent escalation of CHWEP risk is primarily frequency-driven, with a pronounced nationwide emergence starting summer continuing during autumn, while its severity remains comparatively stationary. In detail, the statistically significant increases of CHWEP total days in summer and autumn indicate a seasonal expansion of CHWEP events beyond the traditional summer period in the study region. The CHWEP severity remains comparatively consistent but still exhibiting marginal increase. We also find that the spatial distribution of the CHWEP hotspots differ by characteristics—high frequency concentrates along the western coastal corridor, whereas the highest severities occur in the southeastern inland. This result highlights the contrast between distinct “chronic exposure” versus “acute impact” regimes within the study region. Overall, our findings using the ground observation data well present that the recent CHWEP events have surpassed the historical envelope of variability, therefore underscoring the urgent need for compound-aware risk frameworks in the mid-latitude monsoon regions as global climate change accelerates.