The problem with hot cities
The world is getting hotter, and our cities often bear the brunt of the extreme heat we experience in the summer months in Australia. We’ve all experienced walking along a hot city street, where the heat rising from the concrete and asphalt makes you feel like you’re being baked alive. Scorching streets seem to be a given during the Australian summer, where persistent high temperatures turn our cities into “heat islands”. You’ve probably heard of the urban heat island effect, which occurs when urban areas experience higher temperatures than outlying or rural areas. This difference is caused by how well the surfaces in each environment absorb and hold onto heat.
Urban heat islands are caused due to the impermeable pavements that cover a huge proportion of urban areas. Tree cover has disappeared, grass has been replaced with impenetrable materials, and backyards have shrunk, while building materials that absorb and radiate heat increase exponentially.
Common city materials such as brick, cement, asphalt and steel absorb wavelengths of light energy and convert them into heat. And because these surfaces are impervious, water can’t flow through them to cool them down. This trapped heat has nowhere to go, and causes cities to rapidly become hotter than surrounding areas.
So, why are overheated cities a problem? Sure, it may be uncomfortable in summer, but can’t we all just retreat to our air-conditioned homes and offices and wait for it to pass?
Well, no. There’s a little more to it than that.
Hot cities cause a whole host of problems that are not easy to solve. Higher temperatures cause people to use fans and air conditioners more, leading to excess power use, overloaded energy systems and power outages. People can also become dehydrated and suffer from heat exhaustion more easily. Heat stress is an increasing problem as cities get hotter, and increases levels of heat-related illness and mortality. Dangerously hot conditions cause premature deaths among vulnerable populations, as well as reducing productivity. Studies have shown that worldwide productivity losses due to extreme heat run into the billions annually. And all the heat-generating activities of cities can have significant impacts on microclimates.
Clearly, we need to cool our cities down as much as possible, in order to make them safer, more productive and more comfortable places. There are plenty of strategies in place to help cool cities, including using different building materials and lighter colours. Another more recent strategy is the replacement of traditional city pavements with porous or permeable pavement materials. And this is one of the most effective strategies around, as the massive amounts of impervious material in cities are the biggest cause of the urban heat island effect. Porous pavements are leading the way in reducing urban heat, and are becoming more and more popular in urban building projects.
So, what are porous pavements?
As they sound, porous pavements are a versatile way to allow rainwater to seep through the surface of the pavement material and be absorbed straight into the ground. Rather than water pooling on the pavement, then running off and flooding local waterways, it can be absorbed straight into the ground where it’s needed. Porous paving very effectively reduces runoff, recharges local groundwater tables and increases water infiltration into the ground.
Porous paving can be used in a wide variety of applications in cities, including pedestrian walkways and footpaths, parking lots, courtyards, residential roads and driveways, streetscapes, and tree surrounds. And while it can’t be used in heavy traffic areas, such as highways, high traffic roads and heavy vehicle driveways, it is very effective when used in pedestrian and low volume vehicle traffic areas.
How porous pavements help cool cities
Permeable surfaces offer plenty of benefits for cities, and provide for a cooler urban environment in summer due to the increased circulation of air, water and rain. Plus, the lighter colour of the porous material helps the surface to stay cooler than the traditional darker pavement surfaces. Porous pavements very effectively reduce the temperature in urban environments in summer, cooling cities and reducing the heat island effect. Porous pavers also have high thermal conductivity, and can transfer heat more quickly to the ground, thus reducing heat output. Water and rain will drain through the pavement surface and circulate through the environment, helping to cool things down even further. This smart pavement will absorb water in a similar way to natural landscapes, and help city communities stay safe and comfortable in an increasingly warm environment.
And it’s not just about helping cities stay cooler. There are plenty of other environmental benefits of porous paving too, such as preventing flooding during periods of heavy rainfall, and reducing the run-off of chemicals and pollutants into the environment. Permeable pavements also support sustainable development and align perfectly with green building practices.
Cool pavements are an emerging technology that is being increasingly embraced worldwide as urban communities work to provide a safer and more comfortable environment. Record-breaking temperatures seem to be a way of life nowadays, and take a staggering toll on urban environments. Hot cities pose a serious threat to the health and wellbeing of city dwellers, and also to our environment as a whole. Porous pavements are a highly effective way of reducing the summer sizzle often found in cities and the dangers caused by extreme heat. For your next urban building project, consider installing porous pavers – you can discover more here.
Can porous pavers cope with traffic? 