Urban Heat Islands and Trees

Why cities are hotter than surrounding areas, how concrete, traffic and lost greenery trap heat, and how trees, water bodies and design can cool cities.

Cities are often several degrees hotter than nearby rural areas. This is the urban heat island effect.

Causes

Concrete and asphalt absorb and store heat.
Lost trees and green spaces that would cool through shade and evaporation.
Traffic, industry and ACs release heat.
Dense buildings block breezes.
Filled-in lakes and water bodies.

Effects

Higher temperatures, especially at night.
More cooling demand, raising electricity use.
Health risks during heatwaves.

Cooling cities

Trees: shade and evapotranspiration can cool streets significantly. Trees are one of the cheapest cooling tools.
Parks and green corridors.
Restoring lakes and water bodies.
Cool roofs and cool pavements that reflect sunlight.
Urban design that allows air flow.

Economic value of trees

Studies estimate that urban trees provide large economic benefits through cooling, cleaner air and stormwater management, often exceeding their cost.

India’s cities

Cities like Bengaluru, once known for its lakes and greenery, have seen green cover and water bodies decline, contributing to rising temperatures. Some cities have launched tree-planting and lake restoration programmes.

The shaded street

Two nearby streets in a city differ mainly in tree cover. On a summer afternoon, the tree-lined street is noticeably cooler, and shops there see more customers.

Thinking planting trees is only for beauty

Trees provide cooling, cleaner air and economic benefits.

Key takeaways

Cities are hotter than rural areas due to concrete, traffic and lost greenery.
Urban heat islands raise cooling demand and health risks.
Trees, parks, water bodies and cool surfaces cool cities.
Urban trees often provide benefits exceeding their costs.