Urban planning must factor in wind flow to combat city heat, experts urge

UPDATE - follow-up to Letting the wind flow freely is the secret to cooling our cities: Urban experts point out that dense high-rise buildings and paved surfaces continue to slow down near-ground wind speeds across Indian cities, intensifying heat stress for pedestrians. Terrestrial stilling, a worldwide drop in surface wind speed, has been active since the 1980s. Amruthraj M.N., a consultant with the Sustainable Energy Lab at the Indian Institute for Human Settlements in Bengaluru, notes that surface level refers to about 10 meters from the floor where pedestrians walk. Dense infrastructure and high-rise buildings disrupt wind flow and create turbulence, according to Aaron Serre, a meteorologist from the University of Alabama in Huntsville. Furthermore, replacing vegetation with asphalt and concrete cuts down evapotranspiration and worsens the urban heat island effect.

Urban Design

Metropolitan cities feature high compound walls, podiums, and closely clumped high-rise buildings that restrict wind corridors. When wind hits these tall structures, it can be forced downwards in a downdraught effect or funnelled through narrow spaces to create gusts via the Venturi effect, observed in cities like London and Jaipur. Prasad Vaidya, a senior adviser at IIHS, explains that unplanned building forms contribute to lower wind speeds and higher heat stress, and also slow down the dispersal of air pollution. While cities like Stuttgart, Seoul, and Hong Kong use fluid dynamics simulations to improve ventilation, Indian cities have not yet adopted such wind-related studies routinely. Yugank Goyal from IIM Ahmedabad suggests building a homogenised wind record and using satellite imagery to map city ventilation.

Context

Terrestrial stilling and the urban heat island effect combine to make densely built environments feel much hotter and more humid than surrounding areas. Urban planners use computer models and ventilation maps to design layouts that allow cool air to move freely through streets.