As climate change intensifies around the globe, Indians are facing life-threatening heat with increasing frequency. Scientists estimate that moderately and extremely hot temperatures caused nearly 47,000 premature deaths in India in 2015. This year, India experienced weeks of searing heat that were made at least 30 times more likely because of planet-trapping greenhouse gas pollution from burning fossil fuels. Climate change and population growth are expected to contribute to skyrocketing demand for air conditioning in India to keep people safe, and new research published today indicates that low-cost cool roof installations can help to moderate the effects of global warming on A/C demand in Indian cities.

A/C Saves Lives, But Can Trigger Unintended Consequences

Air conditioning (A/C) can deliver lifesaving benefits for people exposed to dangerous heat. While A/C is only accessible to about 6% of Indian households right now, the India Cooling Action Plan (ICAP) projects that the countrywide cooling demand will grow by a factor of eight in 2037–2038 compared to a 2017–2018 baseline. A/C units in homes, schools, and commercial buildings can help to keep people safe from dangerous temperatures. But, if the electricity to power cooling is supplied by fossil fuels, this climate adaptation response can worsen ambient air pollution and climate change itself. Unfortunately, most of India’s current power is generated by burning coal power plants. Fossil-fuelled power plants are key contributors to India’s air pollution and climate-changing carbon dioxide emissions, though the country is making big strides to transition away from fossil fuel-generated power to cleaner, healthier, renewable energy sources.

India's Cooling Action Plan indicates that demand for cooling will projects nationwide cooling demand to grow eightfold by 2037–2038 compared to 2017–2018 (Credit: Susan Lee, adapted from Indian Ministry of Environment, Forests, and Climate Change data)

Cool Roofs Are Low-Cost Climate Adaptation Measures

Beyond air conditioning, Indian cities are implementing a variety of measures through Heat Action Plans to help prepare communities to cope with extreme heat, including provision of public drinking water stations, cooling centres, and implementation of low-cost, passive landcover adaptation strategies such as cool roofs and urban greening. Cool roofs can help to address extreme heat by reflecting some of the sun’s incoming radiation back out to the atmosphere, reducing heat retention in buildings and the need for A/C to cool indoor spaces.

But in the face of multiple drivers that are increasing A/C demand–a warming climate, along with population growth and economic expansion– just how much can cool roofs help to moderate cooling demand at the city level? Our interdisciplinary team of climate, energy, and health experts have been working together to quantify the energy, air quality, and public health benefits of climate actions in Ahmedabad, which launched South Asia’s first Heat Action Plan in 2013 in response to a deadly heatwave in 2010.

Former Ahmedabad Mayor Gautam Shah (center) painting a cool roof with white paint in Ahmedabad, India, in 2018 (Credit: NRDC)

New Science On Energy Savings from Cool Roofs

Our latest findings of the energy system benefits of cool roofs have been published in the peer-reviewed scientific journal Mitigation and Adaptation Strategies for Global Change. We analysed the energy system effects of cool roof installations in the city of Ahmedabad, comparing a baseline year (2018) to a near-term future in 2030. Climate modelling indicates that the average temperature in the city will increase by 0.81°C between 2018-2030. Based on that climate change projection and estimates of population growth and economic expansion, we estimate that total electricity demand in Ahmedabad could increase from about 8,000 GWh in 2018 to almost 15,000 GWh in 2030. Citywide energy demand for A/C is expected to increase by a factor of almost three between 2030 due to the combined effects of climate warming, population growth, and economic expansion. The good news is that, according to our modelling, expansion of renewable energy sources in Gujarat will allow these clean energy sources to meet 9% of cooling energy demand in 2018 to 45% in 2030– helping to improve air quality and human health in the process.

Cool Roofs Can Deliver Energy Savings

To simulate the citywide cooling energy savings achievable from cool roofs, we mapped the extent of modifiable building roof area in Ahmedabad using public Google Earth images. We then estimated the cooling energy demand effects of expanding cool roofs from their current coverage area (5%) to both 12.5% and 20% of city building roof area (from 5 km2 currently to about 13 km2 and 21 km2 coverage in 2030). To estimate how much cool roof installations could moderate cooling energy demand in the city by 2030, we integrated findings from other studies in Indian cities on the cooling energy savings delivered by previous cool roofs installations.

Our research team utilised Google Earth satellite imagery to map the extent of residential roof area in Ahmedabad to understand the energy savings benefits of cool roofs (Credit: Joshi et al., 2022)

Overall, our study found that expansion of cool roofs from 5% to 20% of total roof area could reduce 2030 cooling energy demand in Ahmedabad by 210 Gigawatt-hours (0.21 Terawatt-hours) relative to a future without additional cool roofs. That estimated reduction in cooling energy demand achievable through expanded implementation of cool roofs may sound small, but it is equal to about 10% of the annual power generation of the coal power plant in Ahmedabad, or about 191,000 metric tons of avoided carbon dioxide pollution. Importantly, we found that cool roof installations can more than offset the city’s climate change-driven 2030 increase in cooling demand.

Modeling indicates that, compared to a future without more cool roofs, expansion of cool roofs in Ahmedabad, India can reduce cooling energy demand by moderating indoor temperatures (Credit: Joshi et al., 2022)

From Evidence to Action

The interconnected challenges of reducing climate warming, managing cooling demand, and protecting human health are global problems, not just issues for India to address. Our study establishes a framework for linking climate, land cover, and energy models to help policymakers in other settings better prepare for growing cooling energy demand under a changing climate. 

This work localises national energy and A/C utilisation projections to the city level in order to articulate the energy savings achievable from heat adaptation through expanded cool roof installations by 2030. Our continuing work on this project aims to quantify the additional air quality and human health benefits of climate change mitigation via reduction of emissions from a coal-fired power plant in the city centre. As climate change hazards mount in India and around the world, efforts to better equip cities to cope with extreme heat are more urgent than ever.

Study co-authored by Jaykumar Joshi, Akhilesh Magal, Dileep Mavalankar, and Anjali Jaiswal. This research was supported in part by the Wellcome Trust [Grant #216093/Z/19/Z].

This article is written and published by our project collaborators at Natural Resources Defense Council (NRDC) on their website. 

The research paper is published in the journal ‘Mitigation and Adaptation Strategies for Global Change’ and can be accessed here. Supplemental information and analysis files can be accessed here.