Alternatives to trees
Man-made solutions are preferable to trees in certain circumstances. Depending on the structure, they can be cheaper to assemble and maintain. What’s more, they are often more practical, especially where it is difficult to plant trees due to subterranean restrictions such as cabling.
An Arizona State University study compared the shade performance of trees against lightweight or engineered shade, for example umbrellas, and other urban forms such as building overhangs, tunnels and breezeways. Shade from urban forms proved to be the most effective, followed by trees . Dr Ariane Middel, Assistant Professor School of Arts, Media and Engineering, lead researcher on the project says: "We hope that our results can help cities pick the right shade for the right place and provide more shade cover in places where it's needed." It is still important that cities continue to plant trees, which provide a range of benefits beyond shading, she stresses.
Additional benefits provided by trees include air quality enhancements, carbon sequestration and increased resilience to stormwater. In Madrid, for example, local authorities are planting a “green wall” of 500,000 trees around the city. The plans will see the absorption of around 175,000 tons of CO2 per year and help alleviate the urban heat island effect.
In the UK, heatwaves are now 30 times more likely than in pre-industrial times. According to the Met Office, there is a 12% chance that extreme temperatures, such as those experienced during the UK heatwave of 2018, could become ‘normal’ by the 2050s . While a 12% chance may seem to amount to a remote possibility, that figure would be less than 1% in a natural climate scenario.