Mobile and Sensor Network Monitoring of Urban Heat Waves and Tropical Nights in a Downtown Area of Seoul, Republic of Korea

Increasing trends of urban heatwave and tropical night phenomena have aggravated human health and living environment in urbanized areas worldwide. Climatological increases in air temperature particularly observed in city centers are largely attributed to urban heat island as well as global warming. In the Republic of Korea, the record-breaking daily maximum air temperatures have been frequently reported in the Seoul metropolitan area over the past 3 years. In this study, we investigated the spatial variabilities of surface and air temperatures influenced by land-use / land-cover types in the downtown area of Seoul during the most hottest period of year (1^st week of August, 2019). The four representative land-use / land-cover types such as grassland, playground, paved road, and stream were selected to monitor the diurnal variations of 2-m air temperatures, relative humidity, wind speed/direction, air pressure, and solar irradiation using automatic weather stations. The eighteen locations were additionally selected to capture the diurnal and spatial variations of 2-m air temperature using temperature sensors. In relation to 2-m air temperature, the surface temperatures were manually measured using infrared thermometers at forty locations nearby twice a day. Simultaneously, a cyclist rode a bicycle along a route passing the measurement locations twice a day. The preliminary results showed that the positive deviation of 2-m air temperature observed using a sensor can be up to 4-5°C from that observed at the Seoul meteorological observatory in the daytime. Paved roads (asphalt or concrete) were the most noticeable land cover in the downtown area. Regardless of time of day, the surface temperatures were consistently higher than the air temperature above, implying the positive sensible heat flux from the surface (i.e., surface heating). As human body can gain heat stress not only in the daytime but still in the nighttime, the customized weather service concerning an air temperature at a pedestrian level and land cover is urgent to reduce the damage of heatwave and tropical night to human health.