The impacts of Urban Heat Islands
More than half of the world’s population is living in urban areas, and the temperatures in these zones, already higher than in rural areas, are increasing even faster. As heat waves are more frequent and more severe every year in southern European countries, urban dwellers suffer not only direct consequences, but also from decreased air quality and increased energy demand.
Source : https://upload.wikimedia.org/wikipedia/commons/0/0a/Atlanta_thermal.jpg
In metropolitan areas, temperature tends to be much warmer than in rural areas, because of the heat created by human activities, transport and the high density of buildings constructed in materials that retain heat. And the nighttime temperatures remain high as the buildings and infrastructures keep the heat trapped that cannot be released in the cold night sky.
Effects on energy needs
In comparatively hot climates, the urban heat island effect leads to an increase in energy needs for air conditioning, refrigerating, etc. And this can be costly: as an example, the Heat Island Group estimated this cost for Los Angeles to be $100 million per year in energy.
As the temperature rises, so does the demand for air conditioning. Indeed, when the temperatures are very high, and even more so when there is little to no wind, there tends to be an extensive use of air conditioning and cooling devices, which ends up contributing to an even higher urban heat island. And it contributes to a very high demand of energy, which causes strains on resources. This often leads to blackouts, as energy companies cannot meet the demand.
To continue with our example, it has been estimated that in Los Angeles, for every degree of temperature increase, the energy demand for air conditioning increases of 500MW.
Effects on air quality
The warmer temperatures lead to an increased smog formation; and this is often worsened by higher emissions from power plants that increase their production to meet the demand.
In urban areas, the pollutants are also blocked from scattering and becoming less toxic by the urban landscape, such as buildings and roads, which tend to retain these particles.
Higher temperatures result in increased ozone formation
Nature-based solutions have several co-benefits in the mitigation of urban heat island effects.
As urban areas with dense constructions cannot benefit from the natural cooling effect of vegetation, in order to mitigate this effect, green and blue areas should be developed in and around cities, to reduce the temperature and absorb pollutants. Such a solution can also contribute to the reduction of the demand for cooling energy, as they naturally And they also reduce the demand for cooling energy. This can be in the form of parks, rehabilitation of rivers or lakes in cities, creating green roofs, planting trees in sidewalks, etc.
Using reflective surfaces for rooftops and pavements can also help to lower the temperature.