Characterizing the indicator-based, day-and-night, and climate-based variations in response of surface urban heat island during heat wave across global 561 cities

Increasing surface urban heat island (SUHI) has been reported to be closely associated with a large number of environmental issues. The response of SUHI during heat wave was important for further mitigation proposal. However, it remained unknown whether the response of SUHI during heat wave varies with different SUHI indicators (intensity, frequency and maximum duration), day-and-night contrast, and climate zones, and how to characterize and explain these response variations. Therefore, this paper quantified and explained for these variations in response of SUHI during heat wave across global 561 cities. There were three major findings. (1) The average percentage of response in intensity, frequency and maximum duration at daytime was -20%, -12% and -47%, while it was 10%, 11% and -10% at nighttime. During heat wave, daytime SUHI decreased in the equatorial and arid climates, while nighttime SUHI increased. (2) The attenuated daytime SUHI during heat wave in the equatorial and arid climates resulted from a decrease in latent heat flux and vegetation cooling effect. (3) Increased solar radiation during heat wave contributed to intensified nighttime SUHI, of which energy sources were determined on surface solar absorption. Additionally, differences in evaporation, vegetation, and albedo during heat wave were discussed.