Contrasting moist heat across local climate zones in heat and non-heat waves: Insights from 29 Chinese metropolises

A thorough comprehension of moist heat (MH) variations across Local Climate Zones (LCZ) during both heat wave (HW) and non-heat waves (NHW) is crucial for mitigating heat stress in residents and urban climate. However, the LCZ-based MH differences between HW and NHW, and their climatic disparities, remain unclear. Here we investigated the heat index difference between HW and NHW (Delta HI) of LCZs across six climate zones (29 Chinese cities), based on three-year (2017-2019) hourly air temperature and relative humidity data collected from 675 stations. The results showed that (1) the Delta HI in high-rise LCZs (LCZ 1 and 4) exceeded that of mid- and low-rise LCZs (LCZ 2, 3, 5, 6, and 8) across cities, indicating that high-rise LCZs in non-shaded area face greater heat risks during HWs and therefore require special attention. Nevertheless, LCZ 9, a low-rise LCZ type, still exhibited a higher daytime Delta HI (8.2 C) due to its high coverage of vegetation. This implies that the addition of vegetation in urban planning requires caution, and a re-evaluation of its combined effects on MH from evaporative cooling and increased humidification is quite necessary. (2) The Delta HI of LCZs peaked in the north subtropical (NS) climate zone, followed by mid subtropical and warm temperate, mid temperate, plateau temperate and south subtropical. This suggests that NS cities require greater mitigation of heat stress during HWs. We believe that these results are helpful for better understanding the MH responses of LCZs to HWs and the design of urban heat mitigation strategies.