4. Semiempirical Model for Fine-Scale Assessment of Pedestrian-Level Wind in High-Density Cities

The aerodynamic property of urban areas is a necessary component in current urban planning and design. Rather than the morphological models introduced in Part II, which provides modeling results in several hundred meters resolution, this chapter introduces a semiempirical approach to model the pedestrian-level wind speed at the neighborhood scale. The balance between momentum transfer and drag force in both an averaged sense over an area and a moving air particle is discussed in order to extend conventional frontal area density \( \left( {\lambda_{\text{f}} } \right) \) to a point-specific parameter \( \left( {\lambda_{{{\text{f\_point}}}} } \right) \). Through correlation with data from wind tunnel experiments, \( \left( {\lambda_{{{\text{f\_point}}}} } \right) \) was considered a good index to assess the pedestrian-level wind speed at a test point with multiple input wind directions. Regression equations were developed to map the pedestrian-level wind environment at 1 × 1 m pixel resolution. This modeling–mapping approach requires less computational time and supportive technology than CFD simulations. Meanwhile, the modeling method provides accurate results at high resolution from a practical point of view. Therefore, the modeling results for urban wind environment can be well integrated into the neighborhood-scale design. Using this approach, urban designers can estimate the neighborhood-scale pedestrian-level wind speed and optimize proposed planning at the onset of the planning process.