Contrasting Responses of Urban and Forest Surface Temperatures to Heat Waves

Understanding differences in responses to heat waves between urban and forest sheds light on a possible path to mitigate heat stress in cities. In this study, we attribute the daytime surface temperature differences between urban and forest to atmospheric and surface biophysical factors based upon simulations using the Weather Research and Forecasting (WRF) model over Boston and Phoenix throughout 20 heat wave cases. Further, we examine how such differences in surface temperature between urban and forest change when a heat wave comes, and try to identify the key contributor. Results show that there exist synergistic interactions between heat waves and urban-forest surface temperature differences in Boston, which can be attributed mostly to the surface resistance to water vapor transfer between the land and the atmosphere. By contrast, the urban-forest temperature differences in Phoenix are mainly controlled by aerodynamic resistance, which is barely affected by the heat wave.