A well-known effect of urbanisation is the warming of the local climate relative to surrounding rural areas, creating a phenomenon known as the ‘urban heat island’ (UHI). UHI intensity varies across a city and over time, but temperature differences may reach 9 °C in the UK.
Factors that contribute to a UHI include the thermal properties, height and spacing of buildings, the production of waste heat, air pollution, and differences in land cover and albedo. The UHI effect is important as heat-related stress accounts for around 1100 premature deaths per year in the UK – increasing noticeably in exceptionally hot years. An estimated 8–11 extra deaths occur each day for each degree increase in air temperature during UK summer heatwaves.
As the occurrence and intensity of extreme heat events is set to increase under the changing climate predicted for the UK, there are significant implications for the thermal comfort and health of city dwellers across many parts of the UK. UHI abatement is of significance to those engaged in the development and delivery of climate change adaptation plans, including urban planners, policy makers and health professionals. Urban planning, building design and landscaping can all provide strategies for mitigating the UHI.
Vegetation has a key role to play in contributing to the overall temperature regulation of cities. Informed selection and strategic placement of trees and green infrastructure can reduce the UHI and cool the air by between 2 ºC and 8 ºC, reducing heat-related stress and premature human deaths during high-temperature events.