Accurate knowledge of the aerodynamic characteristics of cities is vital to describe, model, and forecast the behavior of urban winds and turbulence at all scales. Methods to determine roughness parameters can be classed into those that require observations of wind (anemometric or micrometeorologic), and those that are based on the morphology and spatial arrangement of the surface roughness elements (referred to as morphometric
analysis). Both sets of methods are problematic in urban environments.
Different measurement methods (based on, for example, the wind profile, standard deviation of wind speed, and tubulence statistics) may yield quite different results of aerodynamic characteristics at a given site. In addition, many of the measured data reported in the literature are suspect
because of problems of inadequate fetch, effects of tower exposure, inadequate measurement heights, absence of corrections for stability, and failure to include a zero-plane displacement when calculating the roughness length (see fuller discussion by Grimmond and Oke, 1998).
Models based on morphometry differ regarding which aspects of the surface form and structure they take into account (building height, size, spacing, density). None can respond fully to the range and array of building densities in urban areas. Morphometric models yield quite different results across the range of surface conditions commonly observed in North American cities.
We present a summary of a systematic review and evaluation of measured and modeled data in the published literature and make recommendations as to appropriate measurement techniques and the best morphometric methods to use.