Simple ‘blue and green’ solutions in urban planning can help mitigate the ‘urban heat island’ phenomenon, which is increasingly turning our cities into furnaces during the peak summer months.
Environment and urban experts say cities need heat action plans that minimize the use of concrete in buildings, pavements and other infrastructure, boost roof-top and vertical gardens, propagate nature-based cooling solutions in place of air-conditioners, build urban forests instead of parks, and restore water bodies.
A ravaging heat wave scorched large swathes of the north-west and other parts of India in April and May, with temperatures reaching 49 degrees Celsius in some pockets of Delhi.
Various reports and images released by NASA showed how urban concentrations were much hotter than rural areas at night, in what is called the ‘urban heat island’ effect.
The urban heat island effect
An urban heat island is experienced when certain areas in a city report higher heat load than neighbouring areas on the same day. Heat islands cause higher daytime temperatures and reduced night-time cooling.
Experts say the mercury remains high for a longer time in some urban patches because of the rampant use of concrete, steel, glass, asphalt and other materials that absorb heat during the day and emit it at night.
In comparison, areas without such conditions—and where abundant vegetation and water bodies are available—cool faster at night.
“Prolific construction, concretization, and disappearing green spaces and water bodies are aggravating urban heat stress," says Anumita Roychowdhury, executive director, research and advocacy, Centre for Science and Environment (CSE). She advocates the need to intervene at both building and city levels if urban spaces have to be more heat resilient.
Shreya Gadepalli, an urban affairs expert and founder and managing trustee of think-tank Urban Works Institute, views the problem from a different angle. She says cars are the single biggest cause of soaring temperatures in our cities.
“To accommodate their unmitigated increase, we have been building an ever-increasing expanse of paved surfaces—treeless roads, concrete flyovers, and massive amounts of parking—which is turning our cities into furnaces.” If we want less heat, we should have fewer cars, Gadepalli says.
Also see: Urban Heat Islands: A look at why cities are usually warmer than rural areas
Blue and green solutions
Urban experts suggest a combination of blue and green networks— planning based around water bodies (blue) and tree planting and parks (green) through a combination of infrastructure, ecological restoration and urban design to connect people and nature.
Green solutions include urban forests, roads lined with trees, impervious pavements, vertical and rooftop gardens, etc.
Roychowdhury says cities urgently need to implement heat action plans to increase per capita green spaces, expand urban forestry and adopt water-sensitive urban design and planning.
Among other cooling strategies, conserving water bodies, promoting cool roofs and reflective material, implementing effective shading and greenery can help to mitigate urban heat, she says.
Gadepalli agrees, saying the single most important weapon cities can use to cut heat is trees. The right kind of trees, suited to a particular region, can reduce peak temperature by almost 10 degrees.
“How about rebuilding streets to feel like parks, full of tree cover, and turning every roof into a garden? Wouldn’t that be a game-changer?” Gadepalli says.
‘Rely on scientific data, not perception’
Echoing the need for adequate green cover in hot cities like Delhi, climate and sustainability strategist Prarthana Borah suggests that this belief should be backed with scientific data.
“We are all aware that greener areas are cooler. It is accepted that green spaces reduce the impact of heat. But it would help to validate this with scientific data and not make a statement based on perception or experience,” says Borah, director of CDP India.
Bharati Chaturvedi, founder-director of Chintan, an environmental research and action group, advocates the need for massive water harvesting on every piece of land that can absorb and hold water.
The concept of parks will have to be changed, Chaturvedi says. “We don’t need ornamental and manicured stone fountain gardens made during colonial times when it was not a climate change era. We need city forests.”
All the experts unanimously said there was a need to plant substantially large trees that give shade and hold water in their leaves and roots.
Large construction houses, Borah says, should be mandated to create and maintain vertical gardens of local species in public buildings such as malls, hospitals, and office spaces.
Vertical gardens, however, need maintenance and should not be a one-off exercise to “create gardens and let them be”, Borah cautions.
Lubaina Rangwala of WRI India says that apart from trees, our walkways should be made pervious, which is useful both from the flooding and heat angles.
“Impervious surfaces make things worse. We need permeable surfaces that can absorb water. We need nature-based solutions,” says Rangwala, program head (urban development, sustainable cities and transport) at WRI.
Rangwala says there is an urgent need to restore water bodies and natural systems in cities using scientific methods.
A study by Indian Institute of Technology, Bombay, points out how vegetation can help to control rising temperatures in cities. It recommends vertical walls, dense vegetation and city forests to avoid the effects of urban heat islands.
Heat stress fallout
Prolonged exposure to high heat could lead to discomfort, respiratory difficulties, heat cramps, exhaustion, heat stroke or even death in some cases.
A paper published last year by India’s top meteorologists says heatwaves have claimed more than 17,000 lives over 50 years (1971-2019) in India. However, the World Meteorological Organization says there were 25,692 deaths between 1992 and 2020 (28 years) in India due to heatwaves.
Heat stress has a big economic fallout, too. India lost 118.3 billion work hours—the highest for any country—in 2019 due to extreme heat, a Lancet report said.
Global warming will increase work-related heat stress, damage productivity and cause job and economic losses, the International Labour Organization has said.
Rangwala says disrespecting the environment causes huge losses, be it from the economic perspective, environment, productivity or tourism.
“If our cities become unlivable because of heat stress, offices of big companies would prefer to shift to better and cooler places,” Rangwala cautions.
Heat raises cooling demand
NASA images and other studies show that night temperatures remain quite high in urban neighbourhoods while rural areas cool faster.
This results in the increased usage of air-conditioners in urban homes at night, which is a big cause for concern.
“We use ACs, which is counterproductive. The air-conditioners cool the rooms but heat the air outside, adding to the global warming effect,” Rangwala says.
Roychowdhury says inappropriate architectural design and material, poor ventilation, inadequate shading and daylighting are making buildings heat trappers—increasing air-conditioned hours.
Studies show how electricity demand peaks during summer due to the increased use of air-conditioners. “Sometimes, night-time peak demand can be higher than the day-time peak.”
This works against India’s Cooling Action Plan—2019, which calls for a 25-30 percent reduction in cooling demand and 20-40 percent reduction in cooling energy requirements by 2037-38.
And this is happening because adequate measures have not been adopted to control and reduce heat gains in buildings, Roychowdhury explained.
The obsession with fast-paced building construction is promoting new materials without appropriate design and insulation. For instance, buildings using monolithic wall panels made of concrete get heated up more than twice as fast as a conventional burnt clay brick wall.
Also, if the layout of mass housing is not addressed properly, it can compromise with ventilation and daylighting, adding to the heat stress.
Need of the hour: Sustainable cities
While our homes and offices need to be more thermally comfortable to withstand heat and reduce dependence on energy-intensive cooling, our cities need to be designed to counter the heat effect, Roychowdhury says.
“We need public awareness to ensure adoption of passive architectural design for shading, ventilation and daylighting; climate-appropriate material and insulation, and adequate greening of urban spaces,” Roychowdhury says.
All redevelopment and new urban projects, including road infra, should require mandatory targets for plantation, protection of legacy greens and augmentation of per capita green cover, experts say.
This requires explicit approval guidelines and norms, and a compliance strategy to make them measurable and verifiable.
Green norms in building laws should be made stricter, Rangwala says. “Cutting of trees should be a criminal offence. Environmental regulations should be strictly enforced in buildings and housing projects.”
Gadepalli says that to get rid of cars we need public-transport-oriented development, which is often misinterpreted to build skyscrapers with massive parking lots.
To create a truly transit-oriented urban environment, we should embrace the built form of old cities, she says.
“Think low-to-mid-rise buildings, with shared walls to reduce exposed surfaces that are built to the edge of a fine network of human-scaled, walking-friendly, streets and alleyways that remain cool from building shade,” Gadepalli says.
Taking care of the vulnerable
Experts such as Chaturvedi call for systemic changes to deal with the challenge and to protect the vulnerable population.
Among other things, they bat for a shift in working times so that people can start working earlier to escape the hot hours.
“My focus is workers, mainly in the informal economy. Construction workers are among the most vulnerable along with waste pickers, loaders-unloaders, labourers, etc,” Chaturvedi says.
These workers should be willing to start working at 5am at construction sites so that they can go home early, she explains.
“You can’t have waste picked up at 9 because by the time the person finishes, it is going to be past noon when the mercury will hit 45-46 degrees.”
Similarly, people should not expect domestic workers to come in the afternoon. Chaturvedi calls for societal shifts and the need to be more compassionate to make these people a bit more comfortable.
The experts advocate having community spaces in schools, colleges and stadiums that can be a safe refuge for such people, who gather below flyovers and under whatever shade they can find during hot afternoons.
Parks can act as cooling agents for vendors, cobblers, cleaners and all those who make our community run, Chaturvedi says.
According to Borah, a liveable city has access to clean air and good health — a city designed with complete neighbourhoods, accessibility and sustainable mobility, a diverse local economy, vibrant public spaces, and affordability.
Most liveable cities are considered good cities because of these factors, especially mobility, where walking and cycling are possible. Any factor that destroys the ecosystem and hampers the urban biodiversity would not be an environment-friendly way to make a city liveable, Borah says.
Borah says our cities need more than just small changes in planning. “Cities need to be planned better for accessibility, comfort and healthy lifestyles,” she says. And this includes reversing urban heat stress.
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