Urban planning must factor in wind flow to tackle city heat waves

UPDATE - follow-up to Letting the wind flow freely is the secret to cooling our cities: Unplanned high-rise buildings and dense city infrastructure continue to slow down near-surface winds across Indian cities, worsening the experience of extreme heat and humidity.

Urban Wind Stilling

Wind speed near the ground has been dropping globally in a trend known as terrestrial stilling since the 1980s. Amruthraj M.N., a consultant at the Indian Institute for Human Settlements in Bengaluru, notes that this reduction mainly affects the surface level around 10 metres from the floor where pedestrians move. Meteorologist Aaron Serre from the University of Alabama points out that dense buildings disrupt wind flow and increase surface friction. The loss of vegetation alongside the rise of asphalt and concrete also reduces evapotranspiration, which intensifies the urban heat island effect.

Building Design and Airflow

Urban structures like high compound walls and podiums restrict wind movement inside defined wind corridors. When winds hit tall buildings, they can create the Venturi effect by funnelling through narrow spaces into strong gusts, or create the downdraught effect by pushing downwards along structures. Prasad Vaidya from IIHS warns that unplanned buildings directly contribute to lower wind speeds and higher heat stress. Meanwhile, Yugank Goyal from IIM Ahmedabad stresses the need to build a homogenised wind record using consistent anemometer placement and satellite imagery.

Context

Terrestrial stilling combined with rapid urban concrete expansion traps warm air and moisture near the ground in major cities. Addressing this requires incorporating advanced computer simulations like computational fluid dynamics into everyday city planning and master blueprints.