Sustainability
Urban Heat Island
These indicators are measures of the Urban Heat Island (UHI), a phenomenon of higher nighttime temperatures in the urban core compared to the surrounding rural countryside. The UHI results from urbanization and replacing natural land surfaces with materials that retain heat. UHI conditions influence the environmental, social, and economic characteristics of the region. The increase in the number of June days with minimum temperature above ninety degrees and the increase in the average June low temperature are both indications of the UHI. Increases in nighttime temperature reduce human comfort levels, increase energy use, and jeopardize tourism and investment opportunities for the region if people choose to locate elsewhere.
The heat index measures how hot it feels rather than what the actual temperature is. When heat and humidity combine to reduce the amount of evaporation of sweat from the body, outdoor exercise becomes dangerous even for those in good shape. Increases in the nighttime heat index result in shorter periods of relief from the heat during the summer months. Degree days are a measure of time needed to cool or heat a building to a comfortable temperature; this reflects energy demand through the use of air conditioning units or furnaces. The economic consequence of increases in degree days is greater energy costs to maintain comfortable interior climates.
