Bridging mesoscale transport and building scale dispersion models with high resolution urban morphological datasets

Improving the accuracy and capability of urban transport and dispersion models is essential for future urban applications. These models should realistically reflect the presence and details of urban canopy features. Such features markedly influence the flow circulation patterns, turbulence fields, and energy budgets at mesoscales, and then dominate the fine scale flow and corresponding dispersion within and above the building elements and their canopy. Current advances in mapping these urban features with a high degree of horizontal and vertical resolution is making possible (a) improved urban meteorological simulations with advanced urban canopy parameterizations in mesoscale models and (b) advanced models of flow and dispersion within and above urban canopies at building scales. It has been observed that some fraction of fine scale flow within urban canopies move upstream from the imposed mesoscale transport winds; thus, the definition of an upwind boundary conditions including within-canopy wind profiles for building scale modeling is problematic.

We conduct a study in which the external transport fields that drive building-scale dispersion models and the building scale dispersion models both utilize a common set of building data. This setup attempts to bridge the scale gap that currently exists between these type models. For this study, we utilize outputs of simulations from an urbanized version of the Mesoscale Model (Version 5) (MM5) to drive the Hazardous Prediction Assessment Capability (HPAC) model. Building data have been derived from airborne lidar mappings providing resolution at 1 to 5 m resolution. HPAC incorporates such data as shape files while MM5 utilize these data in aggregated form as urban canopy parameters (UCPs) gridded at 1 km resolution. The study venue is Houston Texas. The investigation includes a sensitivity study providing a comparison of the HPAC driven by the UCP and the standard versions of MM5.