Urban building designs trap heat by blocking crucial near-surface winds

UPDATE - follow-up to Letting the wind flow freely is the secret to cooling our cities: Urban planning across Indian metropolitan areas frequently overlooks wind flow integration, as high-rise buildings and dense infrastructure restrict vital near-surface breezes and intensify pedestrian heat stress.

Urban Wind Factors

Surface-level wind speeds have dropped globally since the 1980s in a trend known as terrestrial stilling. Amruthraj M.N., a consultant with the Sustainable Energy Lab at the Indian Institute for Human Settlements in Bengaluru, points out that pedestrian levels roughly 10 meters from the ground experience these reduced speeds. Aaron Serre, a meteorologist from the University of Alabama in Huntsville, notes that dense urban infrastructure increases surface friction and creates turbulence. Furthermore, replacing vegetation with asphalt and concrete cuts down evapotranspiration and worsens the urban heat island effect.

Architectural Obstacles

Many Indian cities feature high compound walls, podiums, and tall buildings built without proper spacing. These rougher surfaces slow down wind and alter its direction. When wind hits high-rise structures, it can create the downdraught effect by pushing air downwards into strong gusts, or the Venturi effect by funneling air through narrow spaces in places like London and Jaipur. Prasad Vaidya, a senior adviser at IIHS, explains that unplanned higher building forms directly contribute to lower wind speeds and extra heat stress.

Planning Challenges

Experts advocate for better city ventilation maps and computer-based modelling techniques like computational fluid dynamics to simulate wind behaviour. However, Yugank Goyal, associate professor at IIM Ahmedabad, stresses the need for a homogenized wind record because current anemometer placements remain inconsistent. Fluid dynamics simulations also face hurdles due to high computer costs and complex fluid mechanics, while foreign examples in cities like Stuttgart, Seoul, and Hong Kong demonstrate how ventilation improvements can be implemented.

Context

Urban microclimates are heavily influenced by the physical layout of buildings and open spaces, which directly shape how heat and air pollution disperse at street level. Incorporating wind analysis into early urban design helps mitigate the severe heat stress experienced by city residents during hot weather.