Urban areas present unique heat-related challenges due to the urban heat island effect, dense populations and complex built environments.
At the same time, cities have the potential to adapt to changing heat risks through effective risk management.
- Cities tend to be hotter than rural areas – this is known as the Urban Heat Island Effect. The impacts of urban heat islands are often worse in areas with high population density.
- Extreme heat can interact with and compound other stressors such as air pollution.
- A variety of government agencies have crucial roles to play in reducing heat risks in cities; including disaster management, health and social services, city planning and meteorological forecasting services.
Urban Heat Islands
Temperatures in cities tend to be hotter than the surrounding countryside due to the prevalence of surfaces that retain heat and release it slowly; this is called the Urban Heat Island Effect.
Cities consist of environments that are intensely modified by humans, which may also lead to hotspots within cities where the temperature is even higher. This is due to factors such as buildings that block wind, the use of dark-coloured paving or asphalt, heat generated by vehicles, air conditioners and industrial facilities, and a lack of vegetation to cool parts of a city (source).
The effects of urban heat islands are often worse in the densest parts of the city with the fewest greenspaces. In cities with wet climates, urban heat island health impacts are worsened by high humidity. Other factors like higher concentrations of air pollution in urban areas can also aggravate the health impact of extreme heat (source).
Heat and Air Pollution
Extreme heat can interact with – and compound the effects of – air pollution. Heat and sun are two ingredients that can intensify ground-level pollution by mixing with nitrous oxide gases (from sources like car exhausts) to create ozone, a pollutant. This is why hot days are often also hazy, which can be detrimental to health – particularly for those with lung conditions like asthma and cardiovascular disease. The combination of heat and air pollution leads to higher death rates than either factor working independently.
When it is hot and there is also air pollution, common public health advice may need to change. For example, it’s commonly suggested to open windows when the air temperature is cooler outside than inside, but this is not advisable when air pollution levels are high. Lastly, when wildfires occur during a heatwave smoke can significantly increase the risk of death (source).
Management and Adaptation Solutions
Detrimental impacts of extreme heat in cities can be reduced with strategic planning, early warning systems, public preparedness, urban design and engineering solutions, legislation, and health interventions that focus on impact prevention.
Information and solutions should be derived and applied across the broad range of disciplines, time scales, and actors already making important strides to manage heat risks.
Role of Municipal Governments and Systems
Cities have a unique potential to adapt to changing heat risks through effective risk management at multiple levels; connecting policies and incentives; and strengthening community adaptation capacity. It is extremely important for cities to undertake heat-related risk analyses and to devise plans for reducing and managing risks.
During extreme heat, failure or weaknesses in city systems can also make urban vulnerability worse. For example, cities that rely on artificial cooling can face regular electricity cuts as grids become overwhelmed during spikes in demand. Electricity cuts can leave people vulnerable to the risks of heat and have knock on impacts on other urban services. In places where water systems do not reach everyone in the city, for example – such as those living in slums and informal settlements – people may not be able to stay sufficiently hydrated to reduce the effects of extreme heat.
Managing heat risks in an urban setting requires cross-departmental collaboration within a city. A mandate to reduce heat risks does not fit squarely within any traditional sector or government department, rather there are a variety of agencies that have crucial roles to play in the overall effort to reduce heat risks. These include disaster/emergency management, health and social services, city planning and meteorological forecasting services.
The fact that heat risk does not fall neatly under one agency is part of the challenge in scaling-up heat action globally. Within a city, any of the agencies mentioned could take the lead in ensuring action across departments, or the city may wish to elevate the mandate to a level above that of department director in order to ensure better collaboration (source).
Seasonal and sub-seasonal preparedness, complemented by short-term heat early warning systems, are key components of heat action plans, health interventions and emergency response actions. All well-functioning action and alert systems rely on strong cross-disciplinary and multi-agency collaboration, with effective communication between stakeholders including national and local governments, universities, media, healthcare and social protection systems, NGOs and humanitarian actors, as well as affected populations.
Location and Context Specific Risk Management
Epidemiological studies, social science, risk assessment and heat forecasting capabilities are fundamental to incorporate the differentiated needs of vulnerable groups into risk planning, and to inform appropriate and effective responses. Multi-disciplinary understandings of the risk context and perceptions are critical to effective intervention design.
Strategic and environmentally sustainable urban and rural development planning that accounts for energy-efficient technical and biophysical solutions are essential for long-term heat risk management. This includes cost-effective improvements to the built environment, especially housing and building design.
Red Cross Red Crescent Climate Centre
Global Cool Cities Alliance (GCCA)
For information on personal cooling and heat illness detection and management, please see our section on managing and adapting to heat in the body.