The Impact of Surface Heterogeneity on Urban-Atmosphere Interactions

Abstract:

Investigating heat and water transfer in urban areas is essential for understanding the influence of urbanization on the local and regional climate as well as the hydrological cycle. The present study investigates the impacts of surface heterogeneity on water and heat transfer in the atmospheric boundary layer. The Weather Research and Forecast (WRF) model is modified so that a more realistic urban representation is used with Large Eddy Simulations (LES). Numerical experiments are then conducted to investigate heat and water vapor transfer in urban areas under different large-scale synoptic conditions. Preliminary results have found that the urban-rural contrast results in an urban heat inland circulation, which enhances the kinetic energy and accelerates the heat and water vapor transfer in the horizontal direction. The urban-rural contrast in terms of surface temperature and momentum roughness length are shown to have significant but different effect on the urban boundary layer. Within urban areas, the small-scale heterogeneity effect is also studied. When the patch size that characterizes the urban heterogeneity scale is comparable to the size of urban area, the simulated results are strongly dependent on the heterogeneity conditions. As the patch size decreases, the simulated results become more similar to those over a homogeneous urban surface.