Aerodynamic parameters (z0, zd and raM) in urban areas

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. Unfortunately our ability to assign values to these parameters remains problematic. This paper provides a summary of a systematic review and evaluation of measured and modeled data in the published literature. Significant differences exist both within and between each set of methods. In this paper we highlight problems and recommend appropriate measurement techniques and the best morphometric methods to model these parameters in urban environments. The implications of uncertainty in predictions are considered in the context of estimates of the aerodynamic resistance (raM). Recommendations are made regarding the probable magnitude of the aerodynamic characteristics of cities