Heatwaves and cool roofs – reimagining concrete solutions to a rising urban problem

Heatwaves and cool roofs – reimagining concrete solutions to a rising urban problem

By Caroline Fouvet

This article originally appeared in GRIHA’s Shashwat Magazine Vol. 3, Issue 3. Read the magazine online by clicking here.

Pedestrians and workers seeking refuge under trees, bus-shades, and flyovers to escape the stifling heat during peak summer— this is a common sight in many Indian cities. When mercury climbs, the official advice is often to ‘remain indoors’, but with current climate trends portending more intense heatwaves, buildings, especially low-cost homes lacking cooling facilities, are no longer safe spaces. Action is needed to protect people from extreme heat, and while 2016 was the year of initiating policies and solutions, 2017 can be the year of action and implementation.

Image: Heatwaves in India per year. Source: TARU Leading Edge, Roadmap for Planning Heatwave Management in India, 2016.

In 2015, between the months of May and June, India experienced one of the deadliest heatwaves in its history. The extreme weather condition claimed 2,500 lives. With temperatures crossing 50°C in the states of Rajasthan, Uttar Pradesh, and Telangana, Indians realized how unprepared and vulnerable they were. Senior citizens, arguably among the worst hit, were reportedly hospitalized for heatstrokes. While the authorities issued urgent advisories on avoiding outdoor activities, ensuring adequate hydration, and suitable clothing, the situation remained grim.

A heatwave is defined as a prolonged period (usually more than five days) of ‘abnormally’ hot weather.1 In India, such episodes have increased in frequency and intensity over the last decade and these extreme conditions are now arriving sooner than expected. According to a recent study, while India experienced an average of less than 500 heatwaves per year until 1990, its number rose to around 580 between 1991 and 2000, and escalated over the following decade to 670 a year. This rising trend is expected to continue. On this, the Intergovernmental Panel on Climate Change is 90% certain noting that, ‘surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heatwaves will occur more often and last longer….’

Image: Rising Number of Heatwave Deaths Since 1992. Source: TARU Leading Edge, Roadmap for Planning Heatwave Management in India, 2016

A public health issue

Since 1992, India has seen a consistent rise in heatwave-related deaths. Figures compiled by the National Disaster Management Authority (NDMA), show that casualties due to heatwaves have almost doubled over the last 20 years, from an average yearly death toll of 668 between 1996 and 2005, it has risen to 1,200 in the next decade. It is no wonder then that the World Health Organization is now being urged to declare climate change as ‘a global public emergency’.

Cities are the most vulnerable

While heatwaves affect people all over India, many of the casualties are concentrated in urban areas. Indian cities are growing fast, and are today home to a third of the population. Rapid urbanization has led to a spurt in infrastructure investments. However, as population density in cities increases, so does the danger posed by extreme heat. This is because congested urban areas and tightly-packed buildings are major contributors to what is known as the urban heat island (UHI) effect. This phenomenon occurs when heat gets absorbed and then released by buildings, concrete surfaces, and asphalt. This process leaves air temperatures in densely built urban areas higher than in the surroundings. Although clearly affected by the climate, much of the UHI effect is within human control. Air pollution and inappropriate building materials are, for example, among the primary contributors.

Image: Urban Heat Island Effect, TARU Leading Edge, Handbook on Achieving Thermal Comfort, Volume I, 2014

Recognizing the need for a coordinated institutional response

For the first time in India, institutional plans to manage the occurrence of heatwaves have been initiated. Concrete steps have been taken at the city level. The city of Ahmedabad, for example, has developed a systematic heatwave management plan and the Urban Health and Climate Resilience Centre, has designed a municipal-level heatwave action plan for the north-western city of Surat which is now being tried in other coastal cities as well. At the regional level, states such as Andhra Pradesh and Telangana have also launched similar plans in 2016 and have issued guidelines to deal with the heatwave crises.

To increase India’s heatwave readiness, the NDMA released the ‘Guidelines for Preparation of Action Plan: Prevention and Management of Heatwave’ in 2016. This was followed by a report by TARU Leading Edge, an organization working closely with a number of cities on urban climate resilience to provide a roadmap for heatwave planning. It suggests that policy responses should be designed to implement both short- and long-term measures that increase the population’s preparedness to face heatwaves. It stresses, for instance, the importance of developing effective medical response systems and strengthening monitoring to analyse risk.

The housing sector’s potential

Government advisories on heatwaves often focus on citizens remaining indoors. However, when temperatures rise well above 40 ̊C, children, elderly, and people with pre-existing health conditions such as heart diseases remain susceptible even when inside. Indoor heat-related dangers pose a particular threat to those living in poverty, under informally constructed tin or asbestos roofs, poorly insulated buildings, or those who work from home. Urban planning and building design are, therefore, important focus areas to reduce heat stress, and are especially important given India’s projected boom in the construction sector.

In a 2010 report, the consulting firm McKinsey estimated that ‘70% to 80% of the India of 2030 is yet to be built’. This represents a staggering 700–900 million sq. metres of commercial and residential space which is yet to be constructed in India every year. For heatwave resilience, this is a remarkable window of opportunity. To seize it, planners and the construction industry must be encouraged to take a sustainable, resilience-focused approach. Tackling India’s housing challenge while protecting the population from heatwaves and other climate risks can go hand in hand.

Cool roofs: An effective alternative

In India, an increasing reliance on electricity for cooling purposes has overshadowed more traditional methods to deal with hot weather. As temperatures rise, so does the demand for air conditioning. It is estimated that a demand for it will rise from 4.7 million units in 2011 to 48 million by 2031. Air conditioning represents about 40%–60% of the total energy load in hot climates on typical summer days in metropolitan areas like Delhi; hence, its increased use will place a significant burden on the grid. Moreover, poorer households, without the luxury of such cooling solutions, will continue to remain vulnerable.

Do inventive, low-cost technologies hold the answer to this problem? Recognizing the importance of housing design in tackling thermal discomfort, TARU Leading Edge tested various cool roof options in houses in Surat and Indore.

This simple principle entails designing roofs that reflect sunlight and absorb less heat. They can be surprisingly effective, delivering a 1o–4o reduction in indoor temperatures. With negligible operational costs (from `25 per square foot to `175), a one-off investment in cool roof technology provides good value for money, with potential reductions of up to 20% on energy bills. Many of these solutions have been part of traditional building practices, and some are more recent technological interventions, but together they hold the potential to improve thermal comfort.

The performance of each option was monitored with temperature and humidity data loggers, installed inside and outside buildings with cool roofs, as well as in houses without cool- roof systems. The findings were then compiled into a book for the benefit of builders, architects, and home owners for immediate implementation.

Some of the most striking examples from the book include:

  • Cool Roof Paint: Cooling potential 2°C-4°C; The application of reflective paints to roofs can help reduce the amount of indoor heat by reflecting heat away from the building.
  • Bamboo Shading Screen: Cooling potential: 3°C-4°C; A bamboo shading screen for the roof is placed on a basic support structure which provides an air gap between the panel and roof surface. This creates shade and encourages air flow beneath the panel, reducing temperatures.
  • Green Mat Shading: Cooling potential 2.5°C-3°C; Simply by adding green matting (widely available as a covering for greenhouses to grow plants) can provide shade of up to 70%. This simple, low-cost application makes it an attractive option to increase thermal comfort by reducing the roof surface temperature. It also makes flat terraces more usable during the hot season.
  • Lime Concrete: Cooling potential 2°C-3°C; Lime concrete has traditionally been used as a weathering layer for roofs, mostly for buildings constructed more than 50 years ago. The principle is to install a layer of concrete made with lime-surkhi mortar along with broken bricks as coarse aggregate. This mixture is enhanced with natural water-proofing agents such asjaggery, gall-nut, and bael fruit. The lime concrete can then be covered with terracing material such as tiles.
  • Thermocrete: Cooling potential 2°C-3°C; Thermocrete is a kind of concrete mixed with thermocol (extruded polystyrene) balls. These balls act as air cavities which prevent some amount of heat from travelling through the material. Thermocol balls can be conveniently sourced from packaging industries or manufacturers of bean bags.

Image: Cool roof paint. Source: TARU Leading Edge, Handbook on Achieving Thermal Comfort, Volume II, 2014.

The future of heatwave management

As India braces itself for the inevitable and intense heatwaves, city governments need to develop plans to tackle the phenomenon, and include building design as one of their core adaptation measures. It is clear that the housing sector offers considerable potential to increase heatwave resilience, using sustainable, energy-efficient, and cost-effective measures. While climate change will subject India’s cities to conditions more adverse, policy makers must continue to address the issue, moving from planning to implementation at the earliest opportunity. Additionally, the low cost of many effective adaptation measures means that homeowners and builders do not have to wait to act. The simple fact is that a failure to do so will cost lives, and it will be the most socially vulnerable who will pay the biggest price.


To learn more, read TARU Leading Edge’s Thermal Comfort Handbook Volume I & II, which can be downloaded from our resources library:

TARU Leading Edge: Handbook on Achieving Thermal Comfort within the built Environment: Volume 1

TARU Leading Edge: Handbook on Achieving Thermal Comfort within the built Environment: Volume 2


Cover photo by José Morcillo Valenciano (CC by 2.0)

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