Urban Health Risks In A Warmer World: Urban Heating (Part 1)

by Thomas Hartley

Series Overview

From urban heating and more regular flooding, to increased migration and dangerous levels of air pollution, the negative impacts of anthropogenic climate change are changing the environments where most humans live. Over 50% of the world’s population currently live in urban areas, an estimated 4.4 billion, with this set to increase further in the coming decades; the World Bank predicts that by 2050, 7 in every 10 people will live in cities [1].

In this series, we will look at some of the key problems caused in cities and urban environments by the ongoing climate crisis, real-world examples of these problems and their increasing negative impact, as well as mitigation measures that policy-makers and municipal authorities can adopt. 

It is important to note that the externalities of the climate crisis are not always linear and the effects often spill, compound and have indirect effects that makes reporting on them and explaining them particularly challenging. This issue will be explored in the concluding article of this series.

This first article will focus on the effects of Urban Heating.

Article 1: Urban Heating

Efforts today focus on limiting the global average temperature increase to 1.5°C or less. However, this average masks the much larger increases that will be experienced by many people for significant periods of the year. This is particularly acute in cities and urban environments due to the Urban Heat Island (UHI) effect. 

Urban Heat Island (UHI) Effect

UHIs are characterised as the “temperature difference between the central regions of a city and the surrounding rural areas.” [2] Data on city heating across 400 cities reveals that the impact of UHIs can range between 0.5 – 11°C (the effect is much more pronounced at night), with an approximate average of 4.1°C across Asian and Australian cities and 6°C across European cities [3]. UHIs compound the negative effects of heatwaves, exposing populations to higher than regular temperatures for extended periods of time.
Some of the factors that lead to UHIs are [4]:

  • Reduced Natural Landscapes in Urban Areas
    • Trees and vegetation help cool the hair by providing shade, transpiring water from plant leaves, and evaporating surface water.
  • Urban Material Properties
    • Man-made materials such as pavements or roofing tend to reflect less solar energy, and absorb and emit more of the sun’s heat compared to trees, vegetation, and other natural surfaces.
  • Heat Generated from Human Activities
    • Vehicles, air-conditioners and industrial facilities all produce heat which contribute to Urban Heating. Air-conditioners are particularly pernicious given their escalated use during periods of extreme urban heating, further heating the surrounding urban environment.

Negative Health Impacts of UHIs

“Rapid rises in heat gain due to exposure to hotter than average conditions compromises the body’s ability to regulate its temperature and can result in a cascade of illnesses, including heat cramps, heat exhaustion, heatstroke, and hyperthermia… Heat also has important indirect health effects; heat conditions can alter human behaviour, the transmission of diseases, health service delivery, air quality, and critical social infrastructure such as energy, transport, and water.” [6]

Health impacts are not felt evenly throughout the population, with children and elderly individuals as well as those with pre-existing health conditions particularly vulnerable. For example, in 2019 “heat-related mortality in the ?65 population reached a record high of an estimated 345,000 deaths,” which is approximately 80% higher than the 2000-2005 average [7].

Spatial inequalities in urban areas also distribute the health impacts of urban heating unequally as “lower-income districts within a city are often hot spots due to a lack of green spaces and to the co-location of industrial operations.” [8]

It is also worth noting that UHIs create a myriad of negative environmental impacts, from the increased temperature of surface water flowing downstream from urban areas, to the challenges faced by urban wildlife in adapting to higher city temperatures. 

Case-Study: 2023 South Asia Heatwave 

Between the second and fourth weeks of April this year (2023), much of South Asia was exposed to abnormally high temperatures with two cities in Laos and one in Thailand recording their highest temperatures ever. On April 16 in Navi Mumbai, 13 people lost their lives due to exposure to heat at an outdoor public event whilst a further 600 were hospitalised.

The World Weather Attribution group, a collaboration of scientists and climate impact specialists from across the world that was created to “provide robust assessments on the role of climate change in the [immediate] aftermath of the event” [9], have claimed that this heatwave across Bangladesh and India was made 30 times more likely as a result of anthropogenic climate change. They also concluded that “a heatwave with a chance of occurrence of 20% (1 in 5 years) in any given year over India and Bangladesh is now about 2°C hotter in heat index than it would be in a climate not warmed by human activities.” [9]

What can Cities do?

Managing excessive urban heat has become a key task of urban planners and municipal authorities and many different solutions have been offered. The following is not an exhaustive list. 

  • Albedo & Reflective Paint
    • Albedo is the term used to describe the fraction of light that is reflected by a surface. It has been known for a long time that white coloured paint reduces the temperature of buildings because the surface reflects the light rays rather than absorbs them, in other words it has high albedo. 
    • In Los Angeles, the “GAF Cool Community Project painted one million square feet of school playgrounds, streets, parking lots, and community parks to lower temperatures.” Data collected has shown these surfaces can reduce temperature by up to 12°C. [10]
  • Increased Green Space
    • Increasing the number of natural, green spaces in cities has a positive effect on cooling. Planting trees provides shade, both reducing the amount of direct heat for pedestrians but also stops man-made surfaces such as tarmac and concrete from absorbing heat.
  • Community Cooling Centres
    • Cooling centres are often air-conditioned municipal buildings such as libraries, community and senior centres, schools, and shopping centres. These buildings provide a space for local residents to cool down and reduce the risk of developing heat-related illnesses. 

In conclusion, the Urban Heat Island effect and its ability to compound and localise increasing global temperatures has serious adverse health impacts, which will only be accentuated as the climate crisis progresses. It is important that cities take increased heating seriously and pursue measures to alleviate urban heating in equitable ways that ensure safe outcomes for all residents.

[1] World Bank, https://www.worldbank.org/en/topic/urbandevelopment/overview, accessed 5 June 2023
[2] https://doi.org/10.1016/j.cosust.2018.05.014, accessed 5 June 2023
[3] https://doi.org/10.1016/j.enbuild.2019.109482, accessed 5 June 2023
[4] EPA, https://www.epa.gov/heatislands/learn-about-heat-islands, accessed 5 June 2023
[5] The effect of Urban Heating on power consumption cannot be overstated; it is estimated that “the total power capacity needed to meet the escalating demand for space cooling is expected to jump 395 per cent, from 850 gigawatts (GW) in 2016 to 3,350 GW in 2050” which is an increase in size equivalent to the current generating capacity of India, the United States and Europe combined (IEA, 2018). 
[6] WHO, https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health, accessed 5 June 2023
[7] https://doi.org/10.1016/S0140-6736(21)01787-6, accessed 5 June 2023
[8] UNEP, https://wedocs.unep.org/bitstream/handle/20.500.11822/37314/BTH_ES.pdf, accessed 5 June 2023
[9] WWA, https://www.worldweatherattribution.org/extreme-humid-heat-in-south-asia-in-april-2023-largely-driven-by-climate-change-detrimental-to-vulnerable-and-disadvantaged-communities/, accessed 5 June 2023
[10] https://www.thecooldown.com/green-tech/heat-reflective-paint-los-angeles-cool-community-project/, accessed 5 June 2023

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