Frontal area index: A review of calculation methods and application in the urban environment

The frontal area index (FAI) is an essential parameter for assessing underlying roughness and analyzing urban ventilation corridors. Since the early 1990s, FAI has gradually gained prominence in the urban environmental field. Several FAI calculation methods using various names have been proposed under different research conditions. However, the use of these variant calculation methods and names is confusing and does not match correctly. These differences were discussed and renamed using a unified nomenclature to enable future researchers to clearly identify the differences between calculation methods. Different FAI calculation methods have been recommended in various research scenarios based on scientific studies and usage purposes. In addition, the correlation between FAI and urban environmental parameters was analyzed to guide urban planning and architectural design. Based on the analysis of previous studies, a 100 m grid resolution at the urban scale is recommended when the study area of medium and high-density cities in China, Australia, and Egypt does not have a specific resolution guideline. To assist researchers and engineers, flowcharts of FAI calculations, correlation analysis, and environmental data acquisition at the neighborhood and urban scales are presented. Overall, this review can facilitate the standardized application of the FAI and promote its development in the urban environment field.