Can trees cool cities? On a heatwave afternoon, you already know the answer — if you know where to stand.
The heat you can feel, street by street
Step out in Mumbai on a peak summer afternoon, and the heat doesn’t feel uniform.
In dense, built-up neighbourhoods, temperatures can hover around 43°C. A short drive away, where tree-lined roads and parks break up the concrete, it can drop to nearly 32°C. Move further towards greener edges near the city’s outskirts, and it can fall to 25–26°C.
Same city. Same hour. A gap of more than 10°C.
This isn’t anecdotal. A 2023 data-driven analysis by Sustainable Energy for All (SEforALL) highlights how temperatures within Mumbai vary sharply depending on green cover and built density.
As heatwaves tighten their grip across Indian cities — from Delhi to Bengaluru — this gap is becoming more than a matter of discomfort. It is a growing public health concern.
With summer just getting started, parts of India are already feeling the burn. Photograph: (PTI)
What we feel on our skin is not just climate change.
It is also the design of our cities.
What makes a city hotter?
Cities are built to trap heat.
Concrete, asphalt, and glass absorb solar radiation during the day and release it slowly after sunset. Roads and buildings act like storage units, keeping nights warmer and days harsher.
Trees, soil, and water behave very differently.
They reflect more sunlight, retain moisture, and cool the air through shade and evapotranspiration — the process by which plants release water vapour.
When this natural layer is reduced, cities begin to heat unevenly. This is known as the urban heat island effect, where built-up areas become significantly warmer than their surroundings.
But the more urgent truth is this: heat does not spread evenly.
It intensifies where trees disappear and concrete takes over.
What the data shows
A global analysis published in Nature Communications finds that nature-based solutions — such as trees, parks, and green roofs — can lower urban temperatures by around 2°C on average during hot periods.
At first glance, that may seem modest. But in extreme heat, even a 1–2°C drop can significantly reduce heat stress, lower mortality risk, and ease the load on power grids.
And averages often hide sharper local differences.
There is another important insight: not all green spaces are equal.
Studies show trees can provide of natural cooling by offering shade and increasing atmospheric moisture, effectively reducing the urban heat island effect. Photograph: (Facebook)
Urban trees outperform treeless green areas. Research shows that spaces with dense tree cover are significantly cooler than bare urban surfaces, and even cooler than open grasslands without trees. This is due to a combination of shade, leaf density, and sustained evapotranspiration.
In simple terms, a park without trees is not the same as a shaded street.
India’s shrinking natural infrastructure
A study by WRI India tracking the country’s 10 most populated cities found that between 2000 and 2015:
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Built-up areas expanded by nearly 47% in city cores
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Peripheral zones grew by over 130%
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Water bodies shrank by 15%
Much of this expansion came at the cost of natural infrastructure — green cover, lakes, wetlands, and permeable land. Nearly 44% of new construction occurred on land that once helped recharge groundwater.
The consequences are interconnected.
Heatwaves place enormous strain on the human body, affecting the cardiovascular system, kidneys, brain, and metabolism. Photograph: (PTI)
Less vegetation means less cooling.
Less permeable soil increases flooding.
Together, they create cities that are hotter, drier, and more fragile.
How can cities cool down?
The encouraging part is that solutions already exist — and they are both practical and scalable.
Cooling works best at multiple levels:
Neighbourhood level
These have the strongest impact on outdoor temperatures.
Building level
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Green roofs
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Vertical gardens
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Better ventilation
These help reduce indoor heat and lower energy demand.
Together, they form a layered cooling system — above, around, and within our built environment.
Breaking the heat cycle
Heat in cities often creates a feedback loop.
As temperatures rise, air conditioning use increases. AC units release heat outdoors, which pushes temperatures even higher.
Trees help interrupt this cycle.
By lowering ambient temperatures, they reduce the need for artificial cooling — and the excess heat it generates.
If trees help, why are cities still heating up?
The challenge is not just about planting more trees — it is about how and where they are integrated.
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Space is limited as cities grow vertically
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Ground-level greenery shrinks
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High-rise buildings block airflow
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Scattered trees cannot offset large stretches of concrete
What cities need is not isolated patches of green, but connected networks.
Urban greening has been widely recognized as an effective nature-based solution to mitigate thermal stress Photograph: (PTI)
Urban planning has often treated greenery as an afterthought — something to add once construction is complete. But evidence shows that cooling is most effective when nature is built into the design from the start.
Rethinking what cities grow
India’s urban population is expected to double by 2050. Much of the infrastructure for that future has yet to be built.
This presents a crucial opportunity.
Urban heat is not inevitable. It is shaped — to a large extent — by land use and design, and by the presence or absence of trees.
With thoughtful planning, cities can grow in ways that are not only denser but also cooler, healthier, and more resilient.
Because sometimes, the simplest solution is also the most powerful:
Planting and protecting trees is not just about greenery. It is about shaping the climate of the city itself.
