Elizabeth MacDonald, Assoc. Professor City & Regional Planning
This study sheds light on climate-resilience of cities as they have become key urban challenges today.
In 1985, San Francisco adopted a wind comfort standard in its Downtown Area Plan in response to increasing concerns about the city’s downtown public open spaces becoming excessively windy. After 30 years of implementation, this study revisits the standard and examines its effectiveness in promoting pedestrian comfort. 701 valid samples were collected during 6 months of field study, which combined surveying pedestrians and on-site collection of microclimate data. Statistical analysis and an assessment using the physiological equivalent temperature (PET) show that 11 mph (4.92 m/s), the comfort criterion in places for walking, performs as an effective determinant of outdoor comfort in San Francisco.
The original plan mandated that new developments in five parts of the city, including most parts of the downtown area that were associated with high density or development potential and substantial pedestrian activities, be designed or adopt measures to mitigate ground-level wind current in surrounding public streets and open spaces. To ensure acceptable comfort, the plan required that the equivalent wind speed (EWS) in areas where people are seated and where people are walking should not exceed 7 mph (3.13 m/s) and 11 mph (4.92 m/s), respectively, for no more than 10 percent of the time year round, between 7 am and 6 pm. An additional measure, 26 mph (11.62 m/s) for no more than 1 hour per year, was adopted to secure pedestrian safety (City and County of San Francisco 1985).
This requirement has now been in effect for 30 years in San Francisco as a planning measure to promote comfort in the city’s outdoor spaces. It has influenced the design of many new buildings in its downtown. It has also inspired planners in Toronto, Canada, in developing a similar solution to mitigate the adverse effects of wind (Bosselmann et al. 1990, 1995), and other North American cities like New York City, Boston, and Chicago have adopted similar approaches (American Society of Civil Engineers 2004).
This study revisits San Francisco’s wind comfort standard adopted in the Downtown Area Plan and City Planning Codes in 1985 and examines whether it performs as an effective determinant of outdoor comfort in the city after thirty years of implementation.