Many strategies for a cool Bengaluru

Dealing with heat islands

Bengaluru: City dwellers were in for a shock when Bengaluru’s temperature shot up to 36.4 degrees Celcius on March 29, making it the hottest March day in the last five years. This was 2.2 degrees Celsius higher than the average expected temperature during March last week. It was March’s third hottest day in a decade and the fourth hottest day in the last 15 years. The highest maximum temperature ever recorded was 37.3ºC on March 29, 1996.

Bengaluru has yet to become resilient to rising temperatures and the lack of rain. The rising temperature seems to be a product of manmade events.

“Generally, temperature is a measure of ambient air temperature—a combination of factors such as the sun’s rays and how the atmosphere reacts to it. Since the sun and earth are maintained relatively at the same distance, there is not much change in the sun’s rays. The change is in the larger ground-level climatic and ecological conditions,” explains H S Sudhira, urban researcher with Gubbi Labs.

Thus, any human activity, land use change, and construction contribute to environmental changes. Materials used in construction can be the biggest culprits, though they contribute to the durability of structures.

“Cement and concrete absorb more heat and reflect it later in the evening. It can cause air temperature to rise. When this happens over a large built-up area, it causes heat islands,” explains Sudhira.

Dr Monto Mani, professor at the Centre for Sustainable Technologies and Department of Design and Manufacturing, Indian Institute of Science, details how energy can play a role in creating heat islands. 

“The moment it gets hot, the immediate response is to put on an air conditioner (AC) because energy is affordable, and ACs are cheaper. Running the AC eventually results in cooling a part of the building and releasing the heat outside the building. This adds to the urban heat. Energy sourced far away from the city (e.g., solar power plants in Pavagad or thermal power stations in Raichur) is eventually released as heat within the city.” 

“The thermal storage in urban areas has increased because of excessive building heat sinks. The area of concrete cover has increased; concrete stores heat. Cars move around in the city with air conditioners on. When fuel is used to cool the car and release it outside, it generates more heat,” adds Mani.

‘The problem is in planning’

According to Mallanna Sasalu, who heads a prominent housing company based in Bengaluru, the problem is in the planning. “Bengaluru’s city planning document says that 45 per cent of the land should be open with parks and open spaces, while 55 per cent can be built up. The older parts of the city still have some greenery left, but the newer outer areas have lost a lot of trees,” he says, explaining the impact of burgeoning development on the city.

“The mess was not created by constructors or developers; they built according to city development plans. The mess is a symptom. The original issue is planning. How do you build without a futuristic plan? The planning should consider the environment first and then development. It starts with the cure first. We are trying to cure after the cancer is spread,” he says.

He says the density of development must be brought down because more cement means more heat absorption.

“The city will continue to grow, so the remaining forest areas around Bengaluru must be protected. The city has lost 3/4th of its lakes. The remaining 1/4th of the lakes must be kept cleaner, and they should always have water. The presence of water cools down the city,” he says.

“There are thousands of acres of concretised roads. Every road should have recharge pits beneath it; this will reduce runoff water and floods,” suggests Mallanna.

 Yashaswini Sharma, a Bengaluru-based architect, says there are many things policy can fix. “One can make it compulsory for each city resident to grow a tree. The government can push for use of sustainable materials in construction through incentives, or make it mandatory like rainwater harvesting,” she says.

However, the bigger problem, Yashaswini says, is the development of layouts and urban agglomeration which have consumed open grasslands and green spaces. “Projects like Peripheral Ring Road which are pushed as public purpose initiatives, end up devouring trees. This city has lost its trees, lakes and hillocks due to a consumerist approach,” she rues.

We need to curb the the formation of new layouts and the conversion of agriculture, grasslands, and other open land to development zones. What we need are great, big parks and lakes. If we can’t have them, at least preserve the remaining ones. Every resident must compulsorily grow at least one tree planted into the earth.

What can built-up spaces do?

“You can reduce concrete roads and pavements and genuinely invest in creating green spaces. These green spaces can be on building terraces as well,” says Dr Monto Mani, professor Centre for Sustainable Technologies and Department of Design and Manufacturing, Indian Institute of Science.

“Plants undergo a process called evapotranspiration. Leaves release moisture, humidify, and cool the surroundings. They prevent buildings from absorbing heat and carbon as they grow,” he explains what already built-up spaces can do.

For buildings, Mani says there are some solutions such as installing renewables like photovoltaic cells, which also shade the building while generating electricity. 

“Almost all of Bengaluru’s energy needs can be met this way if building rooftops are effectively utilised without cutting existing trees. One has to think about sustaining on solar energy received within the city’s footprint. This is a vital intervention that can help reduce the overheating of urban spaces” he says.

The government’s claims of renewable sources of energy make individuals consume more energy which eventually translates to urban heat. Mani proposes capping water and electricity usage per person as a strategy. “Such a cap on the energy consumption calculated after apportioning for all usages will make people think twice before spending energy,” he explains.

“Instead of air conditioners, people might adapt by changing to appropriate clothing or designing homes to allow more ventilation and cooling, a process called adaptive thermal comfort and passive climatic response. Our bodies can also adapt, building resilience, and not require an air conditioner, instead of a fan for the entire room,” he says.

“To keep heat at bay, terraces can be redone with clay tiles or other naturally cool materials. If it’s a new construction, clay bricks or laterite bricks and lime mortar may be used. Such structures have lower heat transfer to the interior. Some new paints on the market are also touted to reduce heat,” says Yashaswini Sharma, a Bengaluru-based architect.

She says that the easiest and most natural way to go about it is to grow indoor plants. “There’s nothing better if there’s a scope to grow trees around. Keeping bowls of water also helps. Spaces with ventilation above lintel level roll naturally be cooler as hot air escapes through same,” she says.

Mani lists other interventions. “Pedestrianisation and public transport are the other interventions. Increase green cover as much as possible, and reduce building heat storage capacity by increasing green roofs, passive climatic design, adopting modern heat-reflective paints, etc.,” he adds.

Experts recommend reducing embodied energy in construction (the energy required to complete a project) through locally sourced materials that need lesser transportation energy, better design, recycling and reuse, energy-efficient production, careful lifecycle assessment and energy-efficient construction practices.

Climate action to cool the city

The Climate Action Plan for Bengaluru, published in November 2023, discusses reducing the effects of heat islands on the central business district areas of Bengaluru. It suggests reducing energy demand. “Because the upward mobility of economic classes has increased their purchasing power, formulating a single customised strategy for promoting energy efficiency is a challenge that needs to be addressed,” it states.

The document recommends encouraging energy-efficient buildings by promoting building materials that consume less energy and exploring retrofitting existing buildings to help reduce their overall energy consumption.

“Low-rise buildings with white or green rooftops will drastically reduce cooling needs and improve biodiversity. Municipal authorities need to demonstrate the concept of smart buildings by ensuring that new buildings will be energy-efficient and low-carbon and converting all their existing buildings to energy-efficient and low-carbon ones.

The document proposes effective rainwater harvesting (RWH) systems, which will enhance energy savings in service delivery and reduce emissions because less potable water will need to be pumped. It also recommends a transition to new and renewable energy.