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  • Writer's pictureKate

How to Keep Your Cool: Reduce summer overheating using green infrastructure

We know that having more green space around reduces overheating: Cities are generally a few degrees hotter than the countryside around them. In summer this is mostly due to all the dark coloured hard surfaces absorbing the Sun's energy, getting hot and releasing heat back into the air.

Apart from physically shading buildings and dark surfaces or reflecting sunlight, reducing the amount of energy which is absorbed into the city (which artificial shading or painting things white can also do), plants also transpire and photosynthesise.

Transpiration is where water is drawn up through a plant from the roots by water evaporating from the leaves. This results in evaporative cooling- making plants cooler than artificial surfaces.

Plants also photosynthesise. Photosynthesis converts light energy into chemical energy (the plant uses sun to power converting water and carbon dioxide into sugar), which means there's less energy available to be turned into heat- again, keeping us cooler.

A lot of plant leaves are also surprisingly shiny- they reflect much more light than, say, tarmac- but they don't have the glare that paint does, meaning you get benefits of reduced heating, without the disadvantage of glare.

We discussed planting climbers on walls to reduce overheating through walls: There are other considerations for planting trees, especially on clay soils which can move ("heave") when trees grow fast or are removed. Unluckily in this respect, Derby is on clay- so we just need to be a bit careful here to make sure that big tree species are planted a number of metres from buildings, particularly buildings with poor foundations.

Deciduous trees are really good for reducing summer overheating if planted on the East, West or South side of buildings. Evergreen trees also provide shading- but with the disadvantage that they provide shade in the winter as well as the summer- but if you're keen on particular evergreens, then just be sure to plant them where they're not going to badly overshadow someone else...

Currently, it's not really the right time of year to plant trees as they do best if planted in winter when dormant, so they can establish more easily- meaning it's a great time of year for planning and dreaming about improved greenery.

If you have any green space around you, whether it's your garden, a verge, park or communally owned space outside apartments, check the aspect (which direction the green space is relative to your home or others' homes) and have a think about what sorts of planting could work for you and your neighbours.

If the land you'd like trees on is council owned, or owned by a housing association, you can contact them and ask if it's OK to plant trees or other plants on the land you'd like to improve- provided the land is grass or other soft, diggable surface without pipes and cables etc under it. If the land is on-street or otherwise paved, it's harder (and much more expensive) to plant trees but not impossible: The more the council (and private landowners such as businesses) are asked to plant trees on hard surfaces, the more likely it is to happen- and trees on hard paved areas have a huge impact on the environment- both in terms of nature and how nice it is to be in an area.

If the land is owned by other private owners, you can approach them to see if they'd be supportive of tree planting in the area you'd like to plant or other areas. If you can explain the benefits of tree planting to them, they may well welcome your planting scheme.

If you're interested in looking more into the detail of how trees and green spaces are really, really good for cities and what sorts of trees are good to plant for building shading, the resources page of the Trees for Derby website has some handy links to get started with learning more about benefits of growing plants (including trees, grass, green roofs- everything!).

And come back tomorrow for more resources and and activities aimed at increasing green space and tree cover in our cities!

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