The single-layer urban canopy model in WRF V3.2: recent amendments and offline evaluation using the MOSCEM optimization algorithm with field observations

For an increasing number of applications, mesoscale modelling systems now aim to better represent urban areas. The complexity of processes resolved by urban parameterization schemes varies with the application. The concept of fitness-for-purpose is therefore critical for both the choice of parameterizations and the way in which the scheme should be evaluated. A systematic and objective model response analysis procedure (Multiobjective Shuffled Complex Evolution Metropolis (MOSCEM) algorithm) is used to assess the fitness of the single-layer urban canopy parameterization implemented in the Weather Research and Forecasting (WRF) model. The scheme is evaluated regarding its ability to simulate observed surface energy fluxes and the sensitivity to input parameters. Recent amendments (WRF V3.2; Loridan et al., 2010) designed to improve its applicability to numerical weather prediction are described; this includes a set of morphometric parameterizations of canyon and roof roughness leading to a reduced and physically more meaningful list of inputs. The study shows a high sensitivity of the scheme to parameters characterizing roof properties in contrast to a low response to road-related ones. An offline evaluation of the amended scheme using field observations characteristic of distinct urban environments across the world is performed. Some initial guidelines to prioritize efforts to obtain urban land cover class characteristics in WRF are provided.

Reference

Loridan, T., C. S. B. Grimmond, S. Grossman-Clarke, F. Chen, M. Tewari, K. Manning, A. Martilli, H. Kusaka, and M. Best, 2010: Trade-offs and responsiveness of the single-layer urban canopy parameterization in WRF: an offline evaluation using the MOSCEM optimization algorithm and field observations. Quarterly Journal of the Royal Meteorological Society (in press).