Effect of Surface Hydrological Processes in Urban Climate with Case Study of Green Roofs

During the past decades, large scale of conversion of natural landscapes into built terrains has emerged as the source of many adverse effects that challenge the environmental sustainability of cities under changing climatic patterns. To address these adverse effects and to develop corresponding adaptation/mitigation strategies, physically-based single layer urban canopy model (SLUCM) has been developed and implemented into the Weather Research and Forecasting (WRF) platform. Aiming at improving the accuracy of simulations by coupled WRF/SLUCM, physically-based parameterization of urban hydrological processes have been implemented into the model, including (1) anthropogenic latent heat, (2) urban irrigation, (3) evaporation over water-holding engineered pavements, (4) urban oasis effect, and (5) green roof. The new model was extensively tested in offline (stand-alone) setting against flux tower measurements in a variety of cities. In the current study, we carry out online simulations to investigate the impacts of urban hydrological processes on regional hydroclimate. Compared with field observations in Phoenix and Houston metropolitan areas, results show that the enhanced model is significantly improved in accurately predicting meteorological variables in the urban environment, especially the dew point temperature. Case studies show that green roof is capable of reducing urban surface temperature and sensible heat flux effectively, and modifying local and regional hydroclimate throughout the year. This study sheds new light on seasonal and diurnal variations of the impacts of green roof system under different geographic and climatic conditions. The enhanced WRF/SLUCM model deepens our insight into the dynamics of urban land surface processes and its impact on the regional urban hydroclimate through land-atmosphere interactions.