As climate change accelerates and urbanisation intensifies, cities worldwide face a growing threat: urban heat. Rising temperatures, exacerbated by the urban heat island effect, are endangering public health, straining infrastructure, and hurting economies. Amid the crisis, cities are fighting back with innovative solutions to cool down their streets and protect their residents. From increasing green spaces and reflective surfaces to establishing cooling centres and safety standards for outdoor workers, urban planners and policymakers are experimenting with different solutions, proving that beating the heat is possible. The path to resilience won’t be easy, but cities can weather this storm if they act now.
Urban heat is a serious problem that threatens cities’ health, well-being, and sustainability worldwide. Urban heat refers to the compound consequence of global warming and the urban heat island (UHI) effect, which makes cities hotter than their surrounding rural areas. Urban heat can devastate human lives, infrastructure, ecosystems, and economies, especially during heatwaves and extreme heat events. In this article, we look at what causes urban heat, its challenges for cities, and what solutions and success stories exist to tackle this issue.
What Causes Urban Heat?
Urban heat is mainly driven by two factors: climate change and urbanisation. Climate change is increasing the frequency, intensity, and duration of heatwaves and extreme heat events, which can raise the temperature of cities by several degrees. For example, the 2021 heat wave that hit the Pacific Northwest killed an estimated 1,200 people after temperatures rose to a record-breaking 116F (46.6C) in Portland, Oregon and 108F (42.2C) in Seattle, Washington.
Urbanisation is another factor that contributes to urban heat. As more people move into cities, they replace natural vegetation and soil with buildings, roads, and other impervious surfaces that absorb and re-emit more heat, creating a UHI effect.
UHI can increase the temperature of urban areas by up to 7C during the day and 12C at night compared to rural areas. UHI can also worsen air quality, as higher temperatures increase the formation of ground-level ozone and other pollutants.
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What Challenges Does Urban Heat Pose for Cities?
Urban heat poses multiple challenges for cities.
- Public health risks: Urban heat can cause heat stress, heat exhaustion, heat stroke, dehydration, and cardiovascular and respiratory diseases, especially among vulnerable groups such as the elderly, children, low-income, and minority populations. Urban heat can also exacerbate existing health conditions, such as diabetes, hypertension, and asthma. According to the World Health Organization (WHO), more than 166,000 people died due to heat-related causes between 1998 and 2017.
- Infrastructure damage: Urban heat can damage critical infrastructure such as roads, bridges, railways, power lines, and water pipes by causing them to crack, buckle, melt, or burst. For example, in 2019, a heatwave in France caused a nuclear power plant to shut down due to overheating water used for cooling. Urban heat can also increase the risk of wildfires, destroying buildings and vegetation and releasing harmful emissions.
- Economic losses: Urban heat can reduce the productivity and performance of workers, especially those who work outdoors, such as construction, agriculture, and transportation workers. It can also increase the demand and cost of energy for cooling, which can strain the power grid and lead to blackouts, and can reduce the attractiveness and liveability of cities, which can affect tourism, recreation, and business activities on a global level.
What Solutions and Success Stories Exist to Tackle Urban Heat?
1. Heat Mitigation Strategies
These strategies aim to cool cities by changing how we plan and design the built environment, incorporating vegetation, and reducing waste of heat. Examples include:
- Planting trees and increasing green cover: Trees and plants can provide shade, evapotranspiration, and aesthetic benefits, which can lower the temperature and improve the comfort and well-being of urban residents. For example, Singapore has successfully cooled down parts of its city by planting over 7 million trees and creating more than 300 parks and gardens.
- Installing green or cool roofs: Green roofs are roofs covered with vegetation, while cool roofs feature bright coatings to reflect more sunlight and absorb less heat. Both types of roof can reduce the heat gain and loss of buildings, lower energy consumption and costs for cooling, and enhance the biodiversity and amenities of urban spaces. For example, New York City has installed more than 10 million square feet (929,000 square metres) of green and cool roofs since 2009, reducing the city’s annual greenhouse gas emissions by 16,000 metric tons.
- Replacing regular pavement with cool pavement: Cool pavement has a higher albedo (reflectivity) or permeability (water retention) than regular pavement, reducing the surface and air temperature and stormwater runoff. Cool pavement can be made of concrete, asphalt, gravel, or pavers or coated with reflective or porous sealants. A good example is Los Angeles, California. The city has been testing cool pavement projects since 2017, which have been shown to reduce the surface temperature by up to 11C (51.8F).
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Heat Management Strategies
Heat management strategies focus on protecting people from heat that cannot be mitigated. Some examples are:
- Establishing dedicated cooling centres: Cooling centres are public facilities, such as libraries, schools, community centres, or shelters, that offer air-conditioned spaces, water, and information for people who need to escape the heat, especially those who do not have access to cooling at home. The US city of Chicago, for example, has established over 120 cooling centres across the city, which are open during heat emergencies and can accommodate up to 5,000 people.
- Ensuring everyone has access to reliable energy and indoor cooling: Energy and indoor cooling are essential for coping with urban heat, though many people, especially in low-income and developing countries, lack access to them. Therefore, households and businesses must provide affordable, efficient, and clean energy and cooling solutions, such as solar panels, fans, evaporative coolers, or heat pumps. In 2019, India, a country notorious for extreme summer heatwaves, launched the India Cooling Action Plan, which aims to provide access to sustainable cooling for all by 2038.
- Requiring certain protections for people working outdoors in hot weather: People working outdoors, such as construction, agriculture, and transportation workers, are at high risk of heat-related illnesses and injuries. Therefore, it is essential to provide them with adequate protection from extreme conditions, including regular breaks, shade, water, protective clothing, and training. In 2005, the state of California adopted a heat illness prevention standard, which requires employers to implement a written prevention plan and provide workers with the necessary resources and education.
The Way Forward
Urban heat is a serious problem that threatens cities’ health, well-being, and sustainability worldwide. Urban heat is mainly driven by climate change and urbanisation, which increase the frequency, intensity, and duration of heatwaves and extreme heat events and create urban heat islands that make cities hotter than their surrounding rural areas. Urban heat can devastate human lives, infrastructure, ecosystems, and economies, especially during heat waves and extreme heat events.
Fortunately, many solutions and success stories exist to tackle urban heat, such as heat mitigation strategies that aim to cool cities by changing the way we plan and design the built environment, incorporate vegetation, and reduce waste heat, and heat management strategies that focus on protecting people from the heat that cannot be mitigated, such as establishing dedicated cooling centres, ensuring everyone has access to reliable energy and indoor cooling, and requiring certain protections for people working outdoors in hot weather. By implementing these solutions, cities can become more resilient, liveable, and sustainable in the face of urban heat.
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