In urban hot boxes, the need for a plan

Studies have shown that asbestos, concrete, or metal that is typically used in roofs, trap heat and make indoor temperatures significantly warmer

New Delhi: The barren brown patch around the Marol Naka metro station near Mumbai’s Mithi River is beginning to look green. The effort to plant 10,200 tree saplings here, which will continue over the next six months, is not just another drive by the authorities to meet the annual plantation targets. Three acres in this bustling East Andheri suburb are being converted into an urban forest as part of the city’s climate action plan launched last year.

Three acres in this bustling East Andheri suburb are being converted into an urban forest as part of the city’s climate action plan launched last year. (HT Photo)

It is a carefully chosen site; satellite data shows that the average land surface temperature here rose by 4 degrees Celsius over five years due to the construction of the Metro line that started in 2005, said Deepti Talapade, lead of sustainable cities’ programme at WRI-India, who is working with government agencies on the project. The construction of a station and train tracks modified the landscape, turning it into a heat island.

Mumbai’s heat island

The heat island effect is defined as the rise in temperature in certain city pockets that are heavily concretised with asphalt roads, cemented footpaths and concrete, steel and glass buildings collectively called the “grey infrastructure”. Mumbai, India’s most densely populated city, has been experiencing such localised rise in temperatures in many other locations.

A study by Arup -- a UK-based sustainable development consultancy firm – released this July showed that Ghatkopar East was the hottest area in the city, experiencing temperatures that are 7 degrees Celsius higher than its rural surroundings. In contrast, the Maharashtra Nature Park was the coolest in the city -- 8 degrees C less than Ghatkopar.

Ghatkopar is a classic urban neighbourhood, with 60% of its surface being hard and impervious; the Nature Park’s surface, in contrast, was 74% water and 21% vegetation, making a strong case for promoting nature-based solutions to prevent urban heating, which comes with serious health implications ranging from cramps and heat strokes to fatalities in extreme cases. In April , for instance, 12 people in Navi Mumbai died due to sunstroke while attending a public event in the open. According to the Thane weather observatory, the maximum temperature that day was 38 degrees C.

Rising temperatures – a consequence of both climatic and anthropogenic factors (caused by human activity) – are a raging global crisis. In India, already-warm cities are getting warmer and income inequalities are pushing already-vulnerable citizens into a deeper liveability crisis.

A 2022 study by Lancet titled ‘Countdown on Health and Climate Change’ found a 55% increase in mortalities for adults over 65 years old in India between 2000-04 (20,000) and 2017-21 (31,000). The study attributed this to rising temperatures.

India Meteorological Department data also points to a spurt in the number of heatwave days when the maximum temperature is significantly higher than the normal temperature of a station (over 40 degrees C for plains and 30 degrees C for hilly regions). The number of such days in India increased from 413 in 1981-90 to 575 in 2001-2010 and 600 in 2011-2020.

“India, as it is close to the equator, naturally experiences high temperatures in summer. Moreover, atmospheric circulation patterns favour heat waves naturally. But the frequency and duration of heat waves are increasing due to global warming,” said Madhavan Nair Rajeevan, a distinguished scientist at the National Centre for Earth Science Studies.

Implementing heat action plan

Rising temperatures are not just an outdoor problem. Its intensity is felt indoors as well. Studies have shown that asbestos, concrete, or metal that is typically used in roofs trap heat and make indoor temperatures significantly warmer. However, cities such as Ahmedabad, Jodhpur, and most recently, Hyderabad, which launched India’s first statewide cool-roof policy this year, are pushing for a change in this construction practice.

Through its heat action plan launched in 2013, Ahmedabad has advocated the use of reflective tiles and paint instead. This heat mitigation plan – Ahmedabad was the first city in South Asia to have one -- is to prevent fatalities and adverse health impacts such as those caused by the 2010 heatwave, which led to 1,344 deaths excess deaths when compared to 2009 according to government estimates. A study by the Centre for Health and the Global Environment, University of Washington, in 2018 suggested that actions taken based on HAP have saved a thousand lives yearly since then.

Mahila Housing Trust, a non-profit also part of the HAP-making process, has been helping low-income households modify their roofs over the past decade in nine Indian states. Roshini Suparna Diwakar, a senior researcher at MHT, said solar reflective paints are the most cost-effective intervention. “A can of these paint, which costs approximately ₹5,000, is enough to coat a single house and provide relief for the next five years,” she said.

Carrying forward the lessons from Ahmedabad, MHT recently helped Jodhpur draft its HAP. Phalodi, a town in the same district, in May 2016 recorded the highest temperature of 51 degrees C in India. Diwakar said as part of a pilot project, the city of Jodhpur is modifying the roofs of police chowkis, which turn into heat chambers during the hot summer months.

Dileep Malvankar, director at the Indian Institute of Public Health, who helped prepare the Ahmedabad HAP said using reflective white paints on roofs had resulted in indoor temperatures dropping by 3-4 degrees C.

Scaling up the initiative further, Ahmedabad’s health commissioner Tejas Shah said around 500 houses in a low-income settlement in the city’s Lambha area will be provided ‘cool roofs’ in January 2024 as part of a multilateral project. Malvankar said that as part of the same project, a comparative study will be conducted to study the impact on multiple health parameters, such as blood pressure and blood sugar levels of the inhabitants of the modified buildings and compare this with persons not using cool roofs.

Cool-the-roof campaign

Noting the effectiveness of modified roofs to mitigate heat, Telangana came up with India’s first “cool roof” policy in April this year. Through the policy, it is mandatory to retrofit all commercial, government, and government-assisted buildings with cool roofs, either reflective paint or tiled roofs. Further, all new private construction projects must comply with this new roofing policy.

Arvind Kumar, principal secretary of the municipal administration and urban development department, Telangana, said cool roofs provide thermal comfort and reduce greenhouse emissions and financial costs.

A study published in the Journal of Geophysical Research showed that air-conditioner usage increases ambient temperature by 1 to 1.5 degrees C at night. Kumar said, “This reduction of energy demand and ambient heating will not only be good for individual households but also have a compounding effect at a city level.”

Over the next five years, the state wants to cover 300 sq km of area with cool roofs, including 200 sq km of Hyderabad. “We have already covered this year’s target of 5 sq km in Hyderabad and 2.5 sq km area in rest of the state within the first six months,” Kumar said. He said cool roof coverage of 300 sq km in five years would lead to a one-time carbon offset of 30 million tonnes of carbon dioxide and save the state 600 million units of power annually.

Mitigation solution

However, these adaptive solutions to mitigate urban heat are not restricted to planting trees and modifying roofs alone. As a study by the National Natural Science Foundation of China and others showed, laying footpaths with porous bricks in Guangzhou has helped reduce the pavement surface temperature by 12 to 20 degrees C. In contrast, the ambient air temperature fell by 1 degree Celsius.

While extreme dry heat can be deadly, the combination of heat and humidity can be even worse. In many cities in Kerala, a coastal state , excessive humidity leads to an experience (heat index) akin to 54 degrees C, according to the Kerala State Disaster Management Agency. IMD is yet to standardise the heat index measurement mechanism for India. However, it started a pilot using the US National Oceanic and Atmospheric Administration formula earlier this year.

In Kochi, the authorities, alongside mapping out heat-prone areas and planning strategic greening projects, are working on another overlooked measure to reduce heating. The city is cleaning the canals that crisscross its many parts, said Rajan Chedambath, director of the Centre for Heritage, Environment and Development of Kochi’s civic body.

“Canal restoration also helps in reduction in greenhouse gas emission ,” said Monalisa Sen, senior programme Coordinator at ICLEI-Local Governments for Sustainability, South Asia, which is working with the Kochi authorities on multiple projects to make the city climate resilient.

Urban heat is not only caused by heat trapped by sunlight in the grey infrastructure of the city. She said that by restoring the canals, they are trying to reduce the greenhouse gas emissions released from decomposing organic waste in the canals. Sen said that ICLEI is also studying the impact of mangroves in mitigating urban heat and other climate disasters.

As part of the ongoing Thevara - Perandoor Canal restoration work at Thammanam, waste composting machines and floating islands are being implemented to check the release of greenhouse gases that would otherwise increase the ambient temperature.

While appreciating these initiatives, climate experts said it is essential that city administrations and state governments scale them up to policy-level interventions. But they cautioned against using a one-size-fits-all approach.

“The focus is mostly on creating responses and preparing early warning systems, but not much on mitigation,” said Abhiyant Tiwari from the Natural Resources Defence Council (NRDC), who was involved in the Ahmedabad HAP. He said urban heat and other climatic disasters must be addressed in a targeted manner from the perspective of different government functions like housing, health, and other departments.

Climate policy researcher Aditya Valiathan Pillai, who recently co-authored a Centre for Policy and Research report that studied 37 of India’s heat action plans, said, “While there is a broad bucket of effective solutions, we don’t know how effective they are in different conditions and where they are counterproductive.”

Considering the lack of resources in the governments, he said it is critical to identify where the most vulnerable sections of the population on live and prioritise targeted action in those areas.