Investigating Heatwaves and Thermal Comfort due to different synoptic weather systems in South China Greater Bay Area

The Greater Bay Area (GBA) in South China is a highly urbanized and densely populated megalopolis. Heatwaves (HW) in the region are often attributed to the anomalous subtropical high, as well as tropical cyclones (TC) in the South China Sea/Western North Pacific region. This study investigates the mechanisms, intensity, and trends of heatwaves associated with TCs (TC-HW) and those without TC influence (NonTC-HW) during the May–September season from 1981 to 2019. Spatiotemporal variations of the Universal Thermal Climate Index (UTCI) across the region, highlighting key drivers of thermal comfort, are also examined. Results reveal distinct dynamic drivers for the two HW types. TC-HWs are characterized by anomalous subsidence, a strengthened subtropical high and enhanced atmospheric stability, causing anomalous northwesterly surface winds that suppress sea breeze cooling in the region. NonTC-HWs, on the other hand, are driven by an upper-level Omega Block pattern centered at approximately 35–40°N, which is accompanied by anticyclonic flows that inhibit heat dissipation over GBA. Compared with NonTC-HWs, TC-HWs lead to even warmer daily maximum temperature (T-max) by approximately 0.9°C, while the daily minimum temperature (T-min) difference is minimal. Both TC- and NonTC- HWs exhibit increasing trends in frequency and duration; however only TC-HWs show a rising trend in their amplitude. We also studied the trend of UTCI in GBA; there is an increasing annual trend larger than that of surface air temperature. This can be attributed to rising vapor pressure and declining wind speed in the region. These combined effects are found to be most pronounced in highly urbanized coastal locations compared to inland areas. These findings underscore the significant roles of synoptic and local climatic factors, as well as urbanization, in shaping changes in thermal comfort in this area.