Poor urban neighbourhoods more vulnerable to extended effects of heat

Deaths due to extreme heat and cold are increasing in India. Photo by Ramyajagadish/Wikimedia Commons.

  • India is experiencing one of the worst heatwave spells it has faced in the past few decades with about 200 deaths already recorded this year. Now, a recently published study has warned that poor urban neighbourhoods are more vulnerable to the extended effects of heat.
  • People in densely built, low-income neighbourhoods, with no open green spaces, remain unsheltered from heat even at night.
  • As heat action plans evolve for a few Indian cities, they should take into account thermal indices, not just temperature thresholds, recommends the study.
  • Climate-smart city design can help alleviate the burden of a rise in temperature caused by climate change.

As India stares at one of the longest heatwaves in three decades, which so far has claimed over 200 lives, experts warn that the spell will impact people in poor urban neighbourhoods for weeks after the scorcher is over.

In a study published in the journal Science of the Total Environment in April 2019, researchers mapped and compared exposure to heat between low-income and other neighbourhoods in Delhi (India), Dhaka (Bangladesh) and Faisalabad (Pakistan).

While high and low income neighbourhoods both have heat going up during the day, one’s ability to afford air conditioning (AC), avoid strenuous activities outdoors and presence of shade make a difference in coping with the heat exposure, said co-author Christian Siderius of the Wageningen University and Research (WUR).

But people in densely built, low-income neighbourhoods, with no open green spaces, remain unsheltered from heat even at night. Because, at night, these neighbourhoods, tend to trap the heat of the day and stay warmer.

“And due to a combination of factors when the heatwave is over, poor people will be exposed to extremely high night-time temperatures for many more weeks or even months,” said Siderius, adding that this creates an ongoing health risk.

Instead of just tracking urban heat island or air temperature, researchers assessed the exposure to heat in outdoor microclimatic conditions in terms of thermal indices. They advocated that heat action plans (HAP) be based on thermal indices so as to include factors such as humidity, not just temperature thresholds.

Heat is more than just high temperature and it is influenced by several other factors such as humidity, wind, direct or indirect radiation from the sun and indices take into account these factors and give an idea of how hot one really feels.

“Cities are hotter than rural areas around them (we see differences of up to eight degrees Celsius), especially at night. In dense urban areas where the poor live it is even more so. Then they don’t have AC or well-insulated houses so they can’t escape the heat,” said Siderius, also associated with London School of Economics (at the Grantham Research Institute).

“And finally, while temperatures go down a bit with the onset of the monsoon, humidity increases which means heat indices generally stay high. So it’s not so much an emergency situation, but more of an ongoing health risk,” he said.

Hem Dholakia of Council on Energy, Environment and Water (CEEW), who was not associated with the study, agreed about the increased impact of heat in poorer urban areas.

“Let us say that a poor person living in a tin shed, with little or no ventilation, experiences, on an average, a temperature that is two degrees higher indoors, than the outside temperatures. On a heatwave day, when the outside temperature is 41 degrees Celsius, this person is exposed to a temperature of nearly 43 degrees Celsius,” Dholakia elaborated.

“Once the outside temperature drops to 38 degrees (i.e. the heat wave has passed) the person may still experience 40 degrees indoors. Thus, the exposure for the poor may be prolonged based on housing characteristics. This will drive health impacts,” Dholakia told Mongabay-India.

Additionally, differences in heat exposure mostly depended on where in the city, slums or low-income neighbourhoods are situated.

For example, in Delhi, which recorded its highest ever June temperature, 48 degree Celsius, and where urban parts cover roughly half the total city area of 1500  square kilometres, poor neighbourhoods tend to be found all over the city and also close to the centre of the city.

“Here the influence of all the surrounding concrete, which cools down slowly during the night, is highest. In Pakistan’s third largest city of Faisalabad, poor neighbourhoods are now developing on the outskirts of the city, close to agricultural fields which cool down quicker at night which influences the outdoor temperature to some extent,” Siderius said. In Dhaka, in some slum areas close to water, which – if it flows – can cool down temperatures a bit.

India is experiencing one of the worst heatwave spells in the last several decades. Source: NASA Earth Observatory image by Joshua Stevens, using GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC.

Heatwave spells are increasing in India

According to the India Meteorological Department, a heat wave is declared if the maximum temperature at a recording station reaches at least 40 degree Celsius or more for plains, 37 degree Celsius or more for coastal stations and at least 30 degree Celsius or more for hilly regions.

As per the IMD, the frequency of severe heat waves has increased sharply in the past 15 years due to factors like climate change and urban heat island, a phenomenon where a city experiences a higher temperature than its surrounding rural areas.

The National Disaster Management Authority’s 2016 guidelines on preparation of heat action plan (HAP) states if the maximum temperature of any place continues to be more than 45 degrees Celsius consecutively for two days, it is called a heat wave condition.

This year in Churu in the state of Rajasthan, the maximum temperature hovered near 51 degree Celsius for three days. States such as Gujarat, Haryana, Madhya Pradesh, Maharashtra, Uttar Pradesh and Odisha are also under the heatwave’s grip. Meanwhile in Bihar, over 150 people this year have succumbed to the heatwave, including 90 in four days alone (June 15-18, 2019).

Madhavan Nair Rajeevan, who is the secretary of the Union Ministry of Earth Sciences, told Mongabay-India that the present episode is one of the worst heatwave spells and stressed that heatwave spells are increasing over India.

Mahesh Palawat, who is the chief meteorologist with the private weather forecaster Skymet Weather dubbed it as one of the longest heatwave spells in the past few decades. “Due to continuous dry weather and absence of any pre-monsoon activity, the temperatures increased,” said Palawat.

“65.39 percent of the population (nearly two thirds) was exposed to high temperatures of over 40 degree Celsius in the country on June 10, 2019. 37 percent was exposed to the temperature for more than 10 hours in a day. With many weather stations recording their highest ever temperature in June, this could be one of the worst heatwaves the country has ever faced. The failure of the northeast monsoon, the pre-monsoon showers, cyclone Vayu, and the delayed onset (and progress) of monsoon have been the primary reasons behind the excessive heat during June,” Raj Bhagat Palanichamy, who is senior project associate at WRI India Sustainable Cities, told Mongabay-India.

“The massive crop fire incidents during the month of May made the situation worse as people were left exposed to higher temperatures. Satellite data indicate that around 57 percent of the population was exposed to higher temperatures between 25th May and 6th June. Such massive exposures to extreme heat conditions could be having immense effect on the health of the population, particularly among the weaker sections of the society,” said Palanichamy.

If the record of the past few years is to be considered, the rise in global temperature is not slowing any time soon. As per independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA), earth’s global surface temperature in 2018 was the fourth warmest since 1880 and the past five years are, collectively, the warmest years in the modern record.

According to a CEEW study, a 1.5 to 2 degrees Celsius rise in global average temperatures (above pre-industrial level) will lead to non-linear increases in mortality risks across Indian cities.

Nearly two-thirds of India’s population were exposed to high temperatures of over 40 degrees on 10th June 2019. Data: GFS Temperature Estimates, GPWv4, MODIS (LPDAAC – NASA); Processed by Raj Bhagat Palanichamy using Google Earth Engine.

Heat indices for heat action

Extreme heat can lead to dangerous, even deadly, health consequences, including heat stress and heatstroke. From 1992 to 2015, heatwaves have resulted in 22,562 deaths across India.

The western Indian city of Ahmedabad in Gujarat became the first south Asian city to prepare a heat wave action plan (HAP) in 2013 following the 2010 heat wave that claimed 1,344 lives.

Since its rollout, the plan has prevented about 1,100 deaths each year in Ahmedabad. The plan has been adopted by at least a dozen cities in the country. To activate the plan, colour coded heat alerts are issued based on temperature thresholds determined by the city’s civic body.

But experts argue that temperature thresholds are not enough because the observed health impacts from heat exposure are due to the combination temperature as well as humidity.

Dholakia said studies, like this one, from 2010, which compared heat indices to evaluate public health risk, for New York City, found that the heat index is more reliable in predicting deaths related heat as compared to a single variable such as minimum, average or maximum temperature.

While so far efforts have been directed on developing heat action plans in cities where temperatures reach the high forties (such as Ahmedabad and Nagpur), coastal cities should also have their own HAPs.

“Using the heat index approach, we find people living in cities within India with high humidity ( coastal cities like Mumbai, Chennai) and temperatures that typically reach the high thirties may also be vulnerable to heat health impacts,” Dholakia said.

In fact, as per NDMA guidelines on managing heat exposure, a mix of low temperature with high humidity and high temperature with low humidity can trigger similar levels of heat stress. So 43 degrees Celsius and 40 percent humidity or 33 degrees and 95 percent humidity can trigger similar levels of heat stress.

Suresh Rathi of Indian Institute of Public Health, Hyderabad said the city of Surat in Gujarat, which has a considerable migrant population living in informal settlements, has come out with its HAP incorporating heat index.

“Our research on Surat has shown that there is an increase in night-time temperatures (by 3.7 degree Celsius in 30 years and the humidity levels throughout the year does not go below 60 percent,” Rathi said, stressing that heat index is more important than temperature threshold for Surat city.

“For Surat when we calculate heat-associated deaths then the number of deaths goes up by six per day if we take into account the heat index (when relative humidity is factored with the actual air temperature) in contrast to just considering temperature,” Rathi told Mongabay-India

Further, the combination of high relative humidity and temperature also creates a favourable condition for mosquitoes to flourish. “This is more dangerous for slums where water is stored for longer periods of time,” Rathi said, adding the IMD is also discussing heat index.

Rohit Magotra, Deputy Director of Integrated Research for Action and Development
(IRADe) that is working with three Indian cities (Delhi, Rajkot and Bhubaneshwar) to develop Climate Adaptive Heat Stress Action Plans (HSAPs), said the plans take into account the variation of temperature within cities themselves to chalk out thermal hotspots.

“Using satellite imageries we generated brightness maps (indicating reflectivity of surfaces) to highlight thermal hotspots. Using thermal hotspot maps, survey (of households) hotspots were delineated in each city, marking the slums and squatter settlements. Surveys captured the exposure, vulnerability and impact of heat stress on specific occupations such as street hawkers or vendors, construction workers, traffic
police and others,” Magotra told Mongabay-India.

The plans are also gender-sensitive as they take into account specific concerns voiced by women which would help in better communication, said Magotra.

Underlining the study finding that heat stress thresholds are exceeded for months on end in Delhi, Dhaka, and Faisalabad, paper co-author Tanya Singh said one needs to plan in advance for heat exposure because people are also more vulnerable at the start of the heat season or heatwave as they are not acclimatised to it.

“Especially, when it starts getting warmer suddenly after winter. Also, it’s not only on a heatwave day, particularly, that people die, but it’s also on moderately hot days as well. You have more moderate hot days compared to extremely hot days so the population affected is higher on those days. But the focus is so much more on heatwaves,” Singh, associated with WUR and student at London School of Hygiene and Tropical Medicine, told Mongabay-India.

Low income communities more vulnerable to the impact of the heatwave. Photo by Ankur Jain/Wikimedia Commons.

A window of opportunity for climate-smart cities

The authors suggest that climate-smart city design can help alleviate the burden of a rise in temperature due to climate change.

“Neighbourhoods, and not only the rich ones, should be designed such that they provide shading during the day, but also be intersected or embedded in open green spaces to provide cooling during the night,” they write in the study.

Siderius and colleagues argue that development challenges provide a window of opportunity in the region, as much of South Asia’s infrastructure of the future still needs to be built. There is a choice, to build it, climate-smart. Though Indian summers have always been hot and there have always been poor that coped, one needs to consider that climate has already warmed over the past decennia, and in the past cities weren’t this big and so urbanised.

“Another aspect which we have not touched upon – and which has changed a lot over the past decades – is the combination of air pollution and heat. Being (too) hot and breathing polluted air is a health risk, especially for vulnerable groups,” he said.

Rejeet Mathews, who is the head of urban development at World Resources Institute, India Ross Center for Sustainable Cities, pointed out that urbanisation is not moving in a sustainable way.

“Urbanisation in terms of the construction of buildings, roads and pavements is increasing rapidly in India’s cities. This pace of growth does not spare environmentally sensitive areas such as flood plains, shallow lake beds, tree clusters and results in the overall loss of green cover. Concretisation and the increasing amounts of dry, impervious surfaces exacerbate the urban heat island effect, where temperatures are typically a few degrees hotter than surrounding rural areas,” Mathews told Mongabay-India.

For instance, in Bengaluru, about 85 percent of the floodplains of the city, is built on. This pattern of urbanisation is definitely causing a hotter microclimate, pointed out Mathews.

Mathews also stressed on the importance of considering traditional knowledge in modern constructions as cities lose green cover.

“Considering India will continue to face the brunt of such heat waves and related health and death toll, the microclimate needs to be made more livable and thermally comfortable by using traditional techniques, principles of climatic design and other extreme heat adaptation measures. This applies to both buildings as well as external living spaces and is critical to the more vulnerable lower income groups who do not have the capacity to go out and buy air conditioners and coolers,” she emphasised.

Mathews suggested that tree-lined streets and public parks, rainwater harvesting, water holding ponds, and public drinking water points are some of the measures that need to be adopted in external living spaces.

“Buildings should be oriented in ways that living spaces receive the least amount of heat loads from solar radiation avoiding west and southwest directions where non-habitable rooms such as staircases, storerooms etc. could be placed. Further, building envelopes need to be better designed to ensure mutual shading, buffer verandas, extended shading of openings among other techniques, many of which are forgotten traditional practices,” she added.


Jacobs, C., Singh, T., Gorti, G., Iftikhar, U., Saeed, S., Syed, A., … & Siderius, C. (2019). Patterns of outdoor exposure to heat in three South Asian cities. Science of the Total Environment, 674, 264-278.


Banner image: More than 200 deaths have already been recorded due to heatwave across India in 2019. Photo by Ramyajagadish/Wikimedia Commons.

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