A comprehensive indoor–outdoor urban climate model with hydrology: The Vertical City Weather Generator (VCWG v2.0.0)

Abstract

Urban climate models can predict the environmental impacts of urban development by simulating the exchange processes between the atmosphere and urban surfaces. A comprehensive simulation of urban climate requires adequate representation of the exchanges of momentum, heat, and water between the atmosphere and the impervious, vegetated, or soil surfaces. This study presents the inclusion of hydrological processes in a computationally-efficient urban micro-climate model, the Vertical City Weather Generator (VCWG v2.0.0). VCWG v2.0.0 accounts for not only the interaction between indoor and outdoor environments through parameterizations including building energy, surface energy balance, radiation, and vertical diffusion models, but also the biophysical and ecophysiological behavior of urban vegetation via an advanced hydrology model. VCWG v2.0.0 is evaluated against field measurements from Basel, Switzerland, in 2002, and Vancouver, Canada, in 2008. The model outperforms the previous version by reducing the RMSE of potential temperature, wind speed, and specific humidity by 0.5 K, 0.52 m s−1, and 0.001 kg kg−1, respectively. Inclusion of the hydrology model also improves prediction of sensible/latent heat fluxes with RMSE of 18.1/27.7 W m−2 for the Vancouver case. VCWG v2.0.0 is further assessed by explorations related to seasonal variations, modification of ground vegetation, green and cool roofs, and changes in the Local Climate Zone (LCZ), which are all in reasonable agreement with models and observations in previous studies. VCWG v2.0.0 can be used as a design, prediction, or investigation tool to understand how urban climate variables are influenced as a function of forcing environmental conditions and urban configurations.