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: Ground-level wind speeds continue to slow down across global cities due to dense high-rise construction, worsening urban heat stress and trapping air pollution.

Urban Factors

Wind speed near the ground has dropped worldwide in a trend known as terrestrial stilling since the 1980s. Amruthraj M.N., a consultant at the Sustainable Energy Lab at the Indian Institute for Human Settlements in Bengaluru, points out that surface-level wind reduction mostly affects pedestrians around ten metres from the floor. Aaron Serre, a meteorologist from the University of Alabama in Huntsville, explains that dense infrastructure creates turbulence and surface friction. Furthermore, replacing trees with asphalt and concrete lowers evapotranspiration, intensifying the urban heat island effect.

Building Design

Indian metropolitan areas feature closely packed high-rise buildings, high compound walls, and podiums that block designated wind corridors. When wind hits these tall structures, it can create the Venturi effect by funnelling through narrow gaps into gusts, or trigger the downdraught effect by pushing winds downward. Prasad Vaidya, senior adviser at IIHS, notes that unplanned high-rise forms directly contribute to reduced wind speeds and extra heat stress.

Solutions and Costs

Experts suggest using satellite imagery to map city ventilation and tie these findings into master plans, as proposed by J.S.W. School of Public Policy chair Yugank Goyal at IIM Ahmedabad. Cities like Stuttgart, Seoul, and Hong Kong have assessed ventilation to improve airflow, an approach applicable to Indian cities like Chennai and Mumbai. However, computer-based fluid dynamics simulations needed for these studies remain expensive and require specialized expertise.

Context

Terrestrial stilling reduces the natural airflow needed to replace humid air and disperse pollutants near the ground. Understanding how urban geometry affects local wind patterns remains a key challenge for modern city planning.