Urban Heat Stress: Can Umbrellas be a Substitute for Tree Shade?

Increased exposure to solar ultraviolet (UV) radiation and elevated temperatures can increase health risks among residents in urban environments. Although trees and personal umbrellas are known to offer protective benefits, their relative effectiveness has not been previously quantified. A field study was conducted to evaluate the protective effects of 10 trees and 6 umbrellas exposed to direct sunlight between 11:30 am and 1:30 pm over a 3-day period. Two wet bulb globe temperature (WBGT) monitors, a UV radiation sensor, and a light intensity meter were used to collect systematic measurements under both shaded and unshaded conditions. Trees varied in canopy shape and height; umbrellas were uniform in design. Ambient conditions remained consistent during the study. Both trees and umbrellas reduced visible light intensity and UV radiation by more than 90%. However, neither provided substantial reduction in WBGT, with reductions of less than 20%. Trees and umbrellas demonstrated similar effectiveness in reducing exposure to visible light and UV radiation. Both provided limited mitigation of heat stress. These findings are consistent with published literature and support the use of personal umbrellas as practical alternatives to tree shade in urban settings.