Impact of COVID-19 Lockdown on Urban Heat Island Intensity in the Daejeon Metropolitan City

Abstract

The effect of decreased human activity on the urban heat island intensity (UHII) was analyzed using the observed temperature data of six sites (including one reference area) in Daejeon Metropolitan City from February to May of 2019 to 2021. Depending on the observation site, UHII decreased by approximately 20% in 2020 and 2021 compared to 2019 before COVID-19. The decrease in human activity increased UHII at night and decreased it during the daytime. Consequently, UHII diurnal amplitude increased by approximately 20% in 2020 and 2021 compared to 2019, irrespective of location. The decrease in UHII did not appear to be significantly correlated with natural factors such as wind speed and social distancing steps. In contrast, UHII was correlated with social distancing and significantly reduced air pollutants after COVID-19, with the most significant correlation observed for NO2.