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5 sustainable solutions to help tackle extreme heat in South Asia

From painting roofs to geothermal air conditioning systems, accessible and sustainable cooling tools exist to help address the growing problem of heat stress, which is worsening due to climate change
Umaben Metkal paints the roof of her home in Saraspur, Ahmedabad, with solar-reflective white paint. Mahila Housing Trust has helped more than 2,500 households paint their roofs, which can reduce indoor temperatures by 4-5C. (Image: Ashden)
Umaben Metkal paints the roof of her home in Saraspur, Ahmedabad, with solar-reflective white paint. Mahila Housing Trust has helped more than 2,500 households paint their roofs, which can reduce indoor temperatures by 4-5C. (Image: Ashden)

As the world warms, there is an urgent need to find ways to keep people cool. This year, several deadly records have been set in South Asia: in New Delhi, the highest July temperature in 90 years was recorded, at 43.6 degrees Celsius. In April in Karachi, mercury levels hit 44C – the highest in 74 years.

Last week, the climate analysis coalition Climate Action Tracker published research showing that even if the new pledges made by the world’s governments in the first week of COP26 are achieved, global temperatures would rise by more than 2.4C this century. This coincided with the publication of research showing that with just a 2C global temperature rise, a billion people will be affected by extreme heat stress.

Even at 1.5C of global warming (the aspirational target set by the Paris Agreement), studies have found that deadly heat stress could become common across South Asia. Despite pledges to control greenhouse gas emissions, scientists say the world could reach the 1.5C threshold in a matter of years.

There is therefore a pressing need for sustainable cooling technologies and practices that are both low-carbon and accessible to the poorest people – who are also most at risk of heatwaves. And, crucially, there needs to be grassroots support for the proposed solutions.

“We cannot agree on global multilateral solutions if we don’t have local, appropriate implementation,” said Carlos Alvarado Quesada, president of Costa Rica, speaking in Glasgow on 4 November at an awards ceremony held by Ashden, a UK charity that supports solutions to the problems caused by climate change. “Implementation has to be done locally, respecting women, respecting indigenous communities [and] working together with them.”

This year’s Ashden Awards, attended by The Third Pole, recognised the importance of sustainable cooling. Many of the projects highlighted below are recipients of finance via its Fair Cooling Fund, which aims to scale up “frontline fair cooling solutions”.

1. Empowering women through low-cost solutions

Houses in poor neighbourhoods are usually built from cement, often with plastic covers or tin sheets to keep the rain out. These materials absorb heat, and create hot and stuffy living conditions. As urban populations increase and the impacts of global warming become more apparent, the problems will worsen – with knock-on impacts for sanitation and health. Women are particularly exposed, as their work often takes place within the home.

Mahila Housing Trust (MHT) is a not-for-profit organisation based in Ahmedabad. It works in 10 cities across India to boost communities’ resilience to heat stress. It provides women with advice on how to cool their homes in ways that are easily implemented and affordable: to date, more than 1,600 women have been educated about climate change and how to deal with some of its effects.

A solar-powered lighting system installed on Laxmiben Chavda’s bamboo roof in Ahmedabad, Gujarat
A solar-powered lighting system installed on Laxmiben Chavda’s bamboo roof in Ahmedabad, Gujarat. Resin-coated bamboo mats are compressed to form strong, lightweight panels. According to studies, this type of roof can reduce temperatures by up to 5C. MHT facilitated the lighting system and a loan for Chavda’s roof. (Image: Mahila Housing Trust)

The techniques focus on passive cooling methods – preventing heat from building up within people’s homes. One of the quickest and easiest to implement is painting roofs and sun-facing walls with solar-reflective paint, which can reduce indoor temperatures by 4-5C. According to the Global Cool Cities Alliance, when sunlight hits a light-coloured roof, 80% of its energy is reflected, compared with 5% for a dark-coloured roof.

Cool roofs programmes

Under the Ahmedabad Heat Action Plan (HAP) in India, a partnership between the municipal corporation, Indian Institute of Public Health and the Natural Resource Defence Council, more than 7,000 low-income households’ roofs have been painted white. It is estimated that such initiatives save an estimated 1,100 lives every year.

On a bigger scale, the Million Cool Roofs Challenge is a USD 2 million philanthropic initiative to rapidly scale up the use of solar-reflective roofs as a form of sustainable cooling in developing countries suffering heat stress. Ten teams are awarded grants of USD 100,000. In 2019, one of the finalists was the team from Bangladesh, a country with high humidity levels and where ambient temperatures are already reaching 40C. The Bangladesh team painted the roofs of two factories and 105 other buildings in Dhaka, including a nursery and a school, with average indoor air temperatures falling by more than 7C.

A second easy step MHT advises is to grow potted plants and creepers on roofs, which the charity says can reduce indoor temperatures by 2.5C. Vegetation has been proven to have a cooling effect through shading and evapotranspiration. MHT has helped about 200 houses in Bhopal and Ranchi to do this.

MHT also advises on and helps with renovating roofs. The replacement structures have vents and are made from recycled materials that let more light in without trapping heat. According to MHT, these can reduce temperatures by 6-7C. Finally, the charity trains women on principles for reducing heat stress. For example, said Aneri Nihalani, MHT’s communications officer, considering the orientation of a building during construction can help reduce overheating. Taking these steps can help with the family’s finances as well as their comfort, as they need less electricity to cool their homes.

An ‘Air-Live Ventilation’ roof facilitated by the Mahila Housing Trust, one of the organisation’s sustainable cooling initiatives
An ‘Air-Lite Ventilation’ roof facilitated by MHT at Surekhaben Patil’s home in Ahmedabad. Thirty-five women work alongside Patil in her home-based workspace; the 6-7C reduction in temperatures improves their working environment. MHT has enabled the installation of more than 200 of this type of roof. (Image: Mahila Housing Trust)
President of Costa Rica Carlos Alvarado Quesada at the Ashden Awards in Glasgow, November 2021
President of Costa Rica Carlos Alvarado Quesada presents Siraz Hirani, senior programme management specialist at MHT, with the Ashden Award for Cooling in Informal Settlements (Image: Ashden)

Since 2014, the Mahila Housing Trust has helped more than 2,000 families to adopt heat-resilient measures. In recognition of its work, MHT won the 2021 Ashden Award for Cooling in Informal Settlements, which was presented at COP26.

2. Recycling plastic into heat insulation

CBalance, an Indian consultancy that has also received financial support from Ashden, is working with communities to pioneer passive design solutions.

Two of these turn waste into materials that prevent heat absorption. The first recycles discarded plastic packaging into sheets and insulation boards. These provide shading, reflect solar radiation and insulate dwellings from the heat.

Ecoboard installed by cBalance in India
An insulation board (‘Ecoboard’) made from recycled plastic (Image: cBalance)
Plastic bottles installed on a roof as solar insulation by cBalance
Plastic bottles installed on a roof to capture and store the sun’s heat (Image: cBalance)

CBalance also takes used plastic bottles and turns them into heat-control systems. The bottles are filled with water, sealed and fastened to a roof. The bottles absorb the sun’s heat, reducing the amount absorbed by the building below.

Other solutions being developed by cBalance under Ashden’s Fair Cooling Fund include covering roofs with shiny aluminium foil sheets, windows for ventilation and green roofs.

Vinita Rodrigues, project assistant at cBalance Solutions Hub, said this is a pilot project and has been installed in five houses in the city of Pune so far. Having observed the methods and refined them, she said, cBalance aims to have installed them in 30 structures across Pune and Bangalore by January 2022.

“In the future, our aim is to work with women’s cooperatives models, governments, city utilities and other stakeholders to finance and sustain this endeavour,” Rodrigues said. She stressed the need to build communities’ capacity to address the issue of heat stress, rather than just providing direct solutions.

Alufoil installation to prevent heat stress by cBalance in India
Sheets made from aluminium and insulating materials can be moved across a roof using a curtain-like system (Image: cBalance)

3. Geothermal air-conditioning

The temperature on the surface of the Earth fluctuates constantly. But below the Earth’s surface there is little change in temperature. The founders of GeoAirCon, a company in Pakistan, have harnessed this stability to cool homes down. 

In a GeoAirCon system, a ‘loop’ of underground pipes filled with fluid is installed. Geothermal heat pumps move heat around the system. During the summer, these pipes draw heated water from the building and move it underground. (In winter, the opposite principle applies to warm the house.)

Illustration showing how geothermal air conditioning works, with underground pipes drawing heat from a building
A loop of underground pipes draw heat from a building (Image © GeoAirCon)

According to the company, the temperature of the earth about 8-12 feet below the surface in Pakistan ranges from 21-25C. GeoAirCon systems can therefore cool buildings to this range – a comfortable temperature for the human body. 

GeoAirCon says geothermal systems are twice as efficient in cooling as the most efficient conventional air-conditioning system. Cooling capacity is influenced heavily by the insulation of a building, M Hassamuddin, chief executive of GeoAirCon, told The Third Pole, so use of passive cooling best practices is also advised.

A system costs USD 260-460 to install, and costs significantly less to run than a conventional air-conditioning unit, according to the company. Hassamuddin said that though more suited to houses with outdoor spaces, the technology can be installed in densely populated areas, with an area less than a metre wide required to make the hole for the underground pipes. 

So far, GeoAirCon systems have been installed in 12 buildings in Pakistan. GeoAirCon was runner up for the 2021 Ashden Award for Cooling in Informal Settlements.

4. Low-impact cooling systems

In 2015, 8 million air conditioners were installed in India. That number is expected to grow by 200-300 million in the next 20 years. But traditional air conditioning is expensive, electricity-intensive and often uses greenhouse gases like HFCs, exacerbating the climate crisis.

As well as its cooling initiatives in informal settlements, CBalance is working to reduce reliance on conventional air-conditioning. It promotes passive cooling design and ventilation, fostering cooperation between architects and urban communities through its Fairconditioning programme. Hasan ul Banna Khan, an engineer working on Fairconditioning, told The Third Pole that in most cases a building can maintain a comfortable temperature using just passive design techniques coupled with sustainable cooling systems.

A learning and resource centre in Ahmedabad, Gujarat
A learning and resource centre in Ahmedabad, Gujarat. Large windows create better ventilation, while the white, insulated roof keeps the space 5-6C cooler than outside. (Image: Mahila Housing Trust)

Having reduced the requirement for artificial cooling as much as possible, it also promotes technologies that reduce the energy and greenhouse gas intensity of cooling. 

These include:

• Evaporative cooling, which uses evaporated water to cool air. Unlike conventional air conditioning, this does not use refrigeration, and therefore requires a lot less energy. In one building in Pune, this system reduces the need for conventional AC by 40%.

• Radiant or structure cooling, where cool water is circulated through a building. The technology has been used in 73 large buildings in India, including the Indian Institute of Tropical Meteorology in Pune.

• Use of solar power to chill water.

• Air-conditioning units that are more energy-efficient and emit fewer HFCs.

A radiant cooling system installed by cBalance in India
A radiant cooling system, which circulates cool water throughout a building to maintain a comfortable temperature (Image: cBalance)

5. Vernacular architecture providing sustainable cooling

Architects and builders can also look to traditional materials, techniques and designs, which have kept occupants cool for centuries. In one project in Rudrapur, north Bangladesh, students and architects worked with local architects and craftsmen to create houses for low-income families. Using mud and bamboo alongside manmade materials, they installed openings for cross-ventilation, insulation made from coconut fibre and glass windows.

Traditional stilt houses, such as those found in Assam, also use passive cooling. The structures enable cross-ventilation and shading. The walls, which are left unplastered, promote natural ventilation. Recently, projects have started to combine traditional models with materials to enhance their resilience to extreme weather.

The importance of policymakers and urban planning for sustainable cooling

As global emissions drive temperatures to new highs, there is an urgent need to roll out these methods and technologies more widely, at the same time as taking urgent action to limit global warming. Both Aneri Nihalani from MHT and GeoAirCon’s M Hassamuddin told The Third Pole that finance is the main obstacle to wider adoption of the solutions their organisations offer. Hasan ul Banna Khan from the Fairconditioning programme said there is still a lack of awareness of the impacts of conventional air-conditioning, as well as “a dearth of motivated and skilled architects and engineers in the sustainable building design sector”.

Beyond that, urban planners and policymakers need to step in. In Vietnam, the Hanoi City Master Plan 2030 builds the growing need for sustainable urban cooling into the country’s commitment to be net zero by 2050. It aims to prevent heat build-up throughout the city, using ventilation corridors of green and blue space. 

As South Asia warms and urbanises, cities will need to put similar heat adaptation and mitigation measures at the heart of their development plans.