Feeling the Heat: The Urban Heat Island Effect
The urban heat island (UHI) effect is a phenomenon where urban areas are significantly warmer than surrounding rural areas.
The urban heat island (UHI) effect is a phenomenon where urban areas are significantly warmer than surrounding rural areas. This temperature difference is primarily due to human activities and the built environment. The impact of the UHI effect extends far beyond mere discomfort, affecting air quality, public health, and energy consumption.
Urban surfaces, such as asphalt and concrete, have a low albedo, which means they can absorb more solar energy and release it as heat, raising temperatures. Densely built urban areas using large volumes of asphalt and concrete can trap heat, preventing its dissipation. In addition, industrial processes, transportation, and air conditioning release heat into the atmosphere, contributing further to higher temperatures.
The UHI effect significantly impacts urban areas, including increased public health risks, environmental degradation, economic costs, and social inequities. Cities with one million or more people can be 1-3oC warmer than their surroundings, and in the evening, the difference can be up to 12oC.
Impacts in more detail
Public Health: Elevated temperatures can increase the risk of heat-related illnesses and morbidity. A study of 85 European cities found that the median increase in mortality associated with UHIs during extreme heat was 45%.
Air Quality: UHI can increase high-risk aerosol and NO zones by 21.7% and 53.5%, respectively.
Energy Consumption: The median increase in building cooling energy consumption due to UHI is 19% but can range from 10–120%. This is estimated to translate to a 17% increase in CO2 emissions.
Energy Cost: In the US, a study found that the UHI has increased energy bills by $120 billion between 2008 and 2020.
Water Resources: Increased evaporation from higher temperatures can strain water resources, especially in arid or semi-arid regions.
Ecosystems: The UHI effect can disrupt local ecosystems by altering temperature and precipitation patterns, which can negatively impact biodiversity and ecosystem services.
A variety of strategies can be implemented to address the UHI effect. These strategies should target increasing shade and using more reflective surfaces. Improving air pollution within urban areas by using more sustainable transportation methods can also help reduce potential health risks.
Some actions we can take
Green Infrastructure: Planting trees, creating green roofs, and installing green walls can help to cool urban areas by providing shade, reducing heat absorption, and increasing evapotranspiration.
Urban Planning: Careful urban planning can minimise the UHI effect by incorporating green spaces, using reflective materials, and designing buildings to maximise airflow.
Sustainable Transportation: Replacing car journeys with public transport can help reduce CO2 emissions by 42% if using the bus and 73% if travelling by train.
Energy Efficiency: Improved energy efficiency can save a significant amount of energy, with some estimates suggesting that up to 90% of energy consumption can be saved.
By understanding the causes and impacts of the UHI effect and implementing effective mitigation strategies, urban areas can become more sustainable and create liveable environments for all residents.
