Challenges in developing advanced urban parameterization schemes for the community WRF model

Rapid expansion of urban caused many adverse effects on air quality, energy and water supply/demand, and emergency responses. It is imperative for numerical weather prediction (NWP) models to capture effects of urban forcing on wind, temperature, and humidity on the atmospheric boundary layer structures, so that air dispersion and quality models will benefit from improved prediction of the urban meteorological conditions. To bridge the gaps between traditional mesoscale modeling (with 101-km grid spacing) and microscale modeling (with 101-m grid spacing), we are developing an integrated urban modeling system coupled to the Weather Research and Forecast (WRF)/Noah land surface model as a community tool to address urban environmental issues and to study urban-atmospheric interactions. This urban modeling system consists of different methods to parameterize urban land use, a consistent treatment of canopy resistance for both NWP and air-pollution applications, surface biogenic and anthropogenic emissions maps, remote-sensing land-use and characteristics at urban scale, coupling to computational-fluid-dynamic (CFD) models, and a companion urbanized high-resolution land data assimilation system.

This modeling system was applied to various metropolitan areas (Houston, Oklahoma City, Hong Kong, Tokyo, Salt Lake City, etc.) and evaluated against urban-scale observations, which demonstrated that representing the urban heat island effects is critical to correctly capture not only differential heating caused by urban surface heterogeneities, but also mesoscale wind fields modified by urban areas. The challenging issues for developing such urban modeling system include 1) the degree of complexity of urban models, 2) specification of parameters required by urban models, and 3) initialization of state variables in urban models. We will present and discuss recent results of those applications and future plans to further improve the coupled WRF/UCM modeling system, including the incorporation of new satellite data and building morphological data sets.