Urban development is making our cities noisier, busier, and strangely enough – hotter. There was a time when air conditioning was considered a luxury, but summers in the city have become oppressively warm as heatwaves are becoming more frequent. The need for cooling creates a significant amount of pressure on urban infrastructure and amenities. High temperatures in urban areas are due to a phenomenon known as the Urban Heat Island (UHI) effect. It has become a critical issue in recent years as cities across the world have developed at a rapid pace.
What is Urban Heat Island (UHI) Effect?
Urban Heat Island (UHI) effect is a phenomenon where temperature in urban areas is higher than that of surrounding rural areas. The effect occurs when cities replace natural land cover with pavement, buildings, and other surfaces that absorb and retain heat. Such building materials absorb heat during daytime and emit heat at nighttime, resulting in air temperatures that are 1.8 to 5.4 degrees Fahrenheit warmer during the day and an astonishing 22ºF warmer at night as compared to rural areas. In such scenarios, residents turn to air conditioning to stay cool – which is not only expensive but adds carbon pollution and can make outdoor spaces hotter.
This is persuading urban planners to look towards urban greening strategies to help deliver cooler buildings.
Green Urban Infrastructure
Green urban infrastructure has evolved as a viable option to help cool buildings in urban areas. These include street trees, green facades, green roofing, living walls, vegetated surfaces, and more. An efficient way to enhance and improve the performance of grey infrastructure, green urban infrastructure is defined as an interconnected network of natural areas that help in conserving the natural ecosystem’s value and function, while sustaining clean air and water to benefit people and wildlife. They are known to help manage climate change impacts, reduce urban heat, and improve urban well-being.
Benefits of Green Urban Infrastructure
One of the major benefits of green infrastructure is that they help in cooling buildings. Green roofs and living walls help in reducing surface air temperature in two ways. The added layer of greenery on exterior walls protects them from direct solar radiation, which causes the space to absorb less heat during the day and lose less heat during the night, thus improving the energy efficiency of the building.
Green infrastructure has the ability to regulate ambient air temperatures better and does not contribute towards an increase in urban temperature. Natural ground cover allows local cooling through evapotranspiration, where plants release water vapor into the surrounding atmosphere. According to a study, shading from strategically placed street trees can lower surrounding temperatures by up to 6ºC or up to 20ºC on roads. Green infrastructure helps in mitigating urban heat to a great extent while also providing an array of environmental and societal benefits – from improved health to providing wildlife habitat, to stormwater retention, to providing recreational opportunities for the community.