Use of Unmanned Aerial Vehicles to Explore the Structural Characteristics of Urban Spaces for Outdoor Heat Stress Assessment and Comparative Analysis of Heat Island Cooling Strategies

The urban heat island effect increases heat stress among urban dwellers. In response, many cities are taking measures to reduce this effect. This study sought to quantitatively understand the effects of complicated urban thermal environments and heat island cooling strategies on the human body. Observations from unmanned aerial vehicles and automatic weather stations were used for these purposes. To understand the thermal environment, the physiological equivalent temperature (PET), a heat stress index, was estimated using the open-source pythermalcomfort software. Typical artificial impervious pavement served as the control surface; ground-based albedo-modified (GBAM) covers and shaded urban green spaces (SUGS) served as the experimental surfaces. Spatiotemporal control strategies were used to determine differences in cooling effects among urban areas. The analysis times were 09:00, 11:00, 13:00, 15:00, and 17:00 on all days in August 2022. Spatial conditions were established using the sky view factor that reflects the spatial densities of urban areas. The estimated PET values were 27–35 °C for AIP, 27–45 °C for the GBAM surface, and 26–30 °C for SUGS. The PET of the GBAM surface ranged from a minimum of −0.450 °C to a maximum of 11.120 °C higher than that for AIP, thus imparting high heat stress to the human body. In contrast, the PET of SUGS was lower than that of AIP by −0.850 to −4.550 °C.