Joint Risk Assessment of Humid Heatwave-Heavy Precipitation Compound Events in East China During the Late 21st Century

To address the lack of research on the multidimensional characteristics and combined risks of humid heatwave-heavy precipitation compound events, this study proposes a copula-based compound humid heatwave and heavy precipitation joint risk analysis method (CHHRA) following the identification of such events. This method systematically assesses the multidimensional combined risks of humid heatwave-heavy precipitation compound events in East China under both 'simultaneous occurrence (AND)' and 'at least one occurrence (OR)' scenarios. The main conclusions are as follows: (1) Under return periods of 20, 50 and 100 years, both the average intensity and duration of compound events increase significantly with global warming. Under high-emission scenarios (SSP370 and SSP585), the increase is approximately double the historical level. (2) Spatially, compound events with higher average intensity and longer duration will concentrate in eastern coastal and southern regions. Meanwhile, under both 'AND' and 'OR' scenarios, extreme compound events with shorter return periods will predominantly occur in western inland and northern areas. (3) The combined risk under the SSP585 scenario is substantially higher than under SSP126; the recurrence intervals for 50-year 'AND' and 'OR' events are reduced to within 30 and 5 years, respectively. These findings provide data support for the optimisation of extreme weather monitoring and early warning systems, and offer a scientific basis for policy formulation by emergency management authorities.