Enhancing hydrologic modeling in the coupled WRF-Urban modeling system

With its modification on surface energy and water budgets, urbanization has significant impacts on local and regional hydroclimate and leads to many environmental problems. To investigate the impact of urbanization on regional climate, physically-based single layer urban canopy model (SLUCM) has been developed and implemented into the Weather Research and Forecasting (WRF) model. During the last decade, numerous research efforts have been made to address the adverse effects of rapid urban expansion under future climate challenge with the coupled WRF/SLUCM model. However, due to the lack of realistic representation of urban hydrological processes, simulation of urban climatology by current coupled WRF/SLUCM is inevitably inadequate. Aiming at improving the accuracy of simulations, in this study we implement hydrological processes into the model, including (1) anthropogenic latent heat, (2) urban irrigation, (3) evaporation over impervious surface, and (4) urban oasis effect. In addition, we couple the green roof system into the model to verify its capacity in alleviating urban heat island effect at regional scale. Driven by different meteorological forcings, offline tests show that the enhanced model is more accurate in predicting turbulent fluxes arising from built terrains. Besides, results illustrate that green roof is efficient in decreasing energy loading of buildings, not only cooling demand in summer but also heating demand in winter, through the combined evaporative cooling and insulation effect. With installation of green roof, reduced local air temperature and increased regional precipitation is observed from online simulations. Thus the enhanced coupled WRF/SLUCM model can provide deep insight into the dynamics of urban land surface processes and its impact on the regional hydroclimate through land-atmospheric interactions.