A Multiscale Modeling Framework for the Simulation of Momentum, Energy, and Moisture Transport in Complex Urban Canopies

Understanding the impact of urban form on energy use and evapotranspiration is critical towards optimizing urban water and energy conservation projects. Developing the required understanding is complicated by the large length scale separation between the local scales at which projects are implemented, the processes that drive urban microclimate, and the length scales of the processes that these projects seek to modify. Current models that can include important regional scales do not include local effects and therefore, have a limited ability to evaluate conservation projects. While other models that can resolve three-dimensional urban geometry on a highly refined grid are not coupled to realistic meteorological forcing conditions and or cannot include more than a few buildings/trees. We have developed a highly efficient urban and plant canopy microclimate modeling framework that resolves building and tree scales across urban landscapes. This model is coupled to the Weather Research and Forecasting (WRF) community model to establish the link between small- and large-scale features. Here, we will discuss the general framework and the new submodels for the urban energy and water budgets that we have developed. In particular, we will focus on a new urban tree and building models that uses graphical processing unit (GPU) computing and highly efficient ray-tracing algorithms to calculate the urban energy and water budgets. The models explicitly include the impact of trees and buildings and their interaction with the built environment and local micrometeorology. Initial results from simulations of Oklahoma City will be presented with a focus on the distribution of heat within the urban canopy layer. The results are compared to available field data from the Joint Urban 2003 field experiment.