Wind and the city: An evaluation of San Francisco’s planning approach since 1985

Abstract

In 1985, San Francisco adopted a downtown plan on ground-level wind currents intended to mitigate the negative effects of wind on pedestrians' perceived comfort in public open spaces. The plan mandates that new buildings in designated parts of the city associated with high density or development potential be designed or adopt measures to not cause wind in excess of accepted comfort levels. This study examines whether and to what degree the plan has successfully shaped an urban form that mitigates wind by comparing the ground-level wind environment in 1985 and 2013. A series of wind tunnel tests found that during San Francisco's windiest season when the westerly winds are prevalent, the overall mean wind speed ratio measured at 318 locations in four areas of the city dropped by 22 percent. However, there still exist many excessively windy places that are associated with specific urban form conditions, including streets oriented to have direct exposure to westerly winds, flat façades on high-rise buildings, and horizontal street walls where building façades align. Recommendations based on the findings include incorporating more tangible guidance on the built form conditions, expanding the plan's reach to cover more parts of the city, and learning from strategies used elsewhere. By evaluating the urban form impacts of a wind mitigation policy that has been in place for 30 years, the research offers insights for other cities that have implemented or plan to adopt similar approach and sheds light on issues related to wind comfort in high-density urban areas.

Sustainable Block Design Process for High-Rise and High-Density Districts with Snow and Wind Simulations for Winter Cities

“…For Only Wind Murota [16] Kobayashi et al [17] Ishizaki et al [18] Kim, H et al [15] Meng, X et al [19] Bosselmann et al [20] Arens et al [21] For Wind and Snow…”

“…Anno [22] Smedley et al [23] Yukawa et al [24] Mitsuhashi [25] Yukawa et al [26] Setoguchi et al [27][28][29][30][31][32] Watanabe et al [33] Kim et al [15], Meng et al [19], Bosselmann et al [20] and Arens et al [21] produced useful studies of downtown San Francisco, California, United States, and they demonstrated the environmental impact of high-and mid-rise buildings using wind simulations conducted solely using a wind tunnel which compared San Francisco's wind conditions in 1985 and 2013 using a wind tunnel [15,[19][20][21]. Kim et al [15] suggested that the planning guidelines enacted since 1985 were effective in improving the wind comfort in public spaces.…”

“…Kim et al [15] suggested that the planning guidelines enacted since 1985 were effective in improving the wind comfort in public spaces. Our study applies the wind planning methods from this study to its own research on snow.…”

“…Additionally, Tominaga et al [13] and Okaze et al [14] both developed CFD models of snowdrifts around a building. CFD simulations can be helpful in visualizing the relation between an urban design and snow and wind flows; however, these simulations cannot reliably simulate the complexity and uncertainty of turbulence in real-world conditions when they are applied at an urban scale [9,15]. Therefore, this study uses wind tunnels to analyze the snow and wind flows around a target block.…”

Urban-Design Process with Snow and Wind Simulations: A Study on the Kitami City Hall

“…Bosselmann et al studied downtown San Francisco, California, USA and showed, by simulation using a wind tunnel, that new high-rise developments are causing environmental problems resulting from changes in wind and sunlight conditions [4,5]. Kim and Macdonald compared San Francisco's wind environments in 1985 and 2013, and showed the effect of controlling urban forms in the wind environment using a wind tunnel [6]. Tomabechi et al simulated the effect of snow with a wind tunnel [7].…”