Five ways to reduce urban heat stress
Every year in Ireland we get the famous 'Leaving Cert Weather'. Two weeks ago, Ireland recorded the hottest day of the year so far, as temperatures soared to 25.7C and Met Éireann warned of a ‘tropical airmass’. Generally cities are hit the hardest by heatwaves. Urban landscapes of asphalt, brick, metal and dark rooftops soak up an enormous amount of energy from sunlight and reflect even more light. This energy absorption leads to an urban heat island (UHI) where cities experience higher-than-normal heat temperatures, as compared to surrounding areas. In this article, we take a look at changes that could be made to our built environment to contribute to a drop in temperatures over the summer months.
What is an urban heat island?
In cities, the air, surface and soil temperatures are almost always warmer than in rural areas. This effect is known as the Urban Heat Island (UHI). In fact, the temperature of a city whose population is over 1 million can be 1-3°C more than outside the urban environs. In the evening, the difference can be as high as 12°C. Elevated temperatures from UHIs can adversely affect a community’s environment and quality of life by increasing energy consumption and air conditioning costs, elevating greenhouse gas emissions and air pollution, posing dangers to the aquatic systems, causing potential heat-related discomfort and danger to human and animal health, and posing secondary impacts on weather and climate. There are several ways in which the effects of UHIs can be reduced – let’s take a look at some of them.
1. Light-coloured roofs reflect 50% more light
City rooftops are typically black because the traditionally-used asphalt and tar are waterproof, tough, ductile and easy to apply to complex rooftop shapes and designs. However, black and dull colors absorb lots of solar heat, which results in warmer surfaces. To mitigate the problem of urban heat island, more people are having bright, white roofs installed. The use of light-colored concrete and white roofs is far more effective in reflecting up to 50% more light and lowering the temperature. Additionally, light-colored concrete and white roofs reduce the overall air conditioning demands (and costs).
2. Green roofs for sustainability
Green roofs are a great, sustainable option for reducing the temperature in the city. Green roofing is the practice of planting vegetation on a roof to act as perfect insulators, cooling the surrounding environment and reducing demands for air-conditioning. Plus there’s the added bonus that air quality will improve since plants absorb carbon dioxide and produce fresh air. Green roofs, like the one planned for the Wilton Park, Dublin development helps bring back a piece of nature and create natural habitat for flora and fauna in urban spaces, And on some buildings, a recreational space can be created for people to enjoy.
3. Plant trees to reflect solar radiation
The practice of tree planting within and around cities is an excellent way of reflecting solar radiation, while also decreasing the urban heat island effect. Trees provide shade, absorb carbon dioxide, release oxygen and fresh air and provide a cooling effect. Deciduous trees are ideal for urban areas because they cool the area in summer and don’t block any warmth during the wintertime.
The Wavin TreeTank is a new solution that allows trees to grow and helps to prevent roots from destroying roads and pavements. It provides the roots with water, and access for air and nutrients, whilst at the same time acting as a barrier against the roots causing damage at ground level.
4. Awareness and implementation of heat reduction policies and regulations
The EU directives regarding environmental policies, such as low carbon fuel standards and the uses of renewable energy, can significantly regulate and mitigate the problems of urban heat island effect. Indoor climate solutions and underfloor heating systems using low carbon heat sources such as air source and ground source heat pumps can help to reduce carbon emissions. This, in turn, decreases the effects of climate change and global warming. Initiatives like the The Better Energy Homes Scheme helps to increase adoption of sustainable energy sources by offering home owners up to €3500 for heat pump systems, €1200 for solar thermal systems and €700 towards upgrading central heating controls.
5. SuDS for climate resilience
SuDS (Sustainable drainage systems) mimic natural drainage by storing, infiltrating and slowing the flow of water. The impervious surface in urban environments has lower infiltration and evaporation than natural environments and greater surface run-off. SuDS have a number of benefits including heat reduction through evaporation and flood prevention particularly during periods of high rainfall when surface water runoff increases in urban areas.
Geocellular tanks are particularly effective at increasing the capacity of sustainable drainage system for extreme weather events especially in areas where space for surface storage is limited. Engineered solutions such as vortex flow control valves can also enable precise control of discharge flow rates from drainage, storage attenuation and infiltration/soakaway systems.
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