Assessing Impacts of Built Environments on Hydroclimate through Coupled Land-Atmospheric Modeling

Rapid urbanization and the associated landscape modification can modify surface energy and water budgets, and further modulate dynamic and thermodynamic structures of the overlying atmosphere through land – atmosphere interactions. To investigate urban land – atmosphere interactions, a coupled framework of a single layer urban canopy model (SLUCM) with physical urban energy and water transport processes and a single column model (SCM) for convective atmospheric boundary layer parameterization has been developed. The coupled SLUCM-SCM model was tested against field measurements of surface layer fluxes as well as profiles of virtual potential temperature and specific humidity in the mixed layer under convective schemes. After model test, the SLUCM-SCM was used to simulate urban boundary layer dynamics (i.e. boundary layer height, temperature and humidity) under designed conditions by changing building geometry, roof albedo, vegetation fraction, and roughness length of momentum etc. in the urban surface layer. Furthermore, an advanced Monte Carlo method was used to quantify the sensitivity of atmospheric boundary layer characteristics to the input surface and atmospheric parameters of SLUCM-SCM. Simulation results show that land surface states impose significant impact on the physics of the overlying boundary layer. Overall, this numerical framework provides a novel modeling tool to assess the impacts of urban land surface conditions on the local hydrometeorology. It also has potentially far-reaching implications to urban hydroclimatic and ecohydrological services for cities under future expansion and climate challenges.