Increasing Compound Hazards of Tropical Cyclones and Heatwaves over Southeastern Coast of China under Climate Warming

Compound hazards are more destructive than the individual ones. Using observational and reanalysis datasets during 1960–2019, this study shows a remarkable concurrent relationship between extreme heatwaves (HWs) over southeastern coast of China (SECC) and tropical cyclone (TC) activities over western North Pacific (WNP). Overall, 70% of HWs co-occurred with TC activities (TC–HWs) in the past 60 years. Although the total frequency of TCs over WNP exhibited a decreasing trend, the occurrences of TC–HWs over SECC have been increasing, primarily due to the increasing HWs in the warming climate. In addition, TC–HWs are stronger and longer lasting than HWs that occur alone (AHWs). And in the long-term perspective, both AHWs and TC–HWs exhibit increasing trends, especially since the mid-1980s. The enhancement on HWs caused by TC activities is sustained until TCs make their landfalls and then collapse. Based on composite analysis, TC activities enhance HWs by modulating atmospheric circulations and triggering anomalous descending motion over southern China mainland which intensifies the western Pacific subtropical high (WPSH) and favors increased temperatures therein. Given the severe adverse impacts of TC–HWs on coastal populations, more research is needed to assess the future projections of TC–HWs, as HWs are expected to be more frequent and stronger as the climate warms, whereas TCs over WNP may occur less often.