Trees in parking lots: a guarantee for urban comfort

Trees in parking lots help decreasing pollutants and also reduce temperature on the ground line. Let’s discover its advantages and how to design a shady parking lot.

Has anyone, coming back to a car left under the sun, ever been in discomfort because of excessive heat? Isn’t that true, especially during the summer, when drivers always look for a shaded parking spot? Then why parking lots without trees get designed and built in our cities all the time?

THE URBAN HEAT ISLAND

It may look a trivial concept. When the weather is too warm, being in the shadow is more comfortable than being in full sun, especially if we are in a town. Most people, in their spare time during summer, pile out in available green areas. Only there they can experience a feeling of relief from the oppressive heat that rests on areas with more buildings.

Covering the soil with waterproof structures (like building or roads), together with the pollution created by exhaust gas, creates in fact a pronounced increase of the temperature in urban areas. This is especially clear when compared to green areas as parks, agricultural soils and gardens. This phenomenon is what we are referring when we speak of “Urban heat island”. Leaving the city center the temperature can decrease as much as 5°C (9°F)!

 

THE BENEFITS OF TREES ON URBAN MICROCLIMATE

The shadow generated by the presence of trees leads to a strong reduction of temperature on the ground line, especially when that shadow is cast over paved surfaces. Cars parked in full sun can reach temperature even 25°C-30°C (45°F-55°F) warmer when compared with same cars parked in a shaded spot. If the shadows are due the presence of trees, things get even better. The benefits of trees in terms of pollutants reduction are well known especially when it comes to urbanized environments. Anyway, surely is more pleasant to come back to a car parked in a shady spot than to a car left in the sun!

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PARKING LOTS WITHOUT TREES: WHY?

Unfortunately, in Italy, trees in parking lots aren’t the rule yet. It’s very common to find parking lots that are very sunny, without any tree. The choice to avoid tree plantings can be due different reasons.

• Optimization available space. Tree plantings and relative borders would reduce the space available to vehicles, which would decrease in number.
• Need to reduce the costs. Funding borders and trees with all the needed accessories (banquettes, topsoil, waterings, eventually bushes to cover the soil) can impact on the overall costs of the parking lot.
• Incompetence of the designer. Not every designer necessarily knows about the tree-generated benefits in a markedly artificial environment like a paved parking lot.

 

TREES IN PARKING LOTS: DESIGN TIPS

A well designed parking lot will produce beneficial effects in a short time, allowing for a better liveability of urban areas. But to guarantee a good result in terms of environmental benefits, some precautions have to be taken. Some suggestions to get a well done job when designing a parking lot with trees are shown below.

• Trees need room. Too often the trees are in borders which are too small, borders where they are not allowed to grow properly and where they can’t express their full potential. Because of this, it’s very important to design a border, for trees, that will be big enough to ensure that at least some soil surface will remain permeable and will allow roots development.
• Waterproof surfaces should be reduced as much as possible. The paving of large surfaces insulates the soil from the air and creates problems of asphyxiation on roots. Designing parking spots which use turf as soil cover, instead of paving, especially when using permeable interlocking pavers, allows the water/gas exchanges, improving physical/chemical characteristics of the soil.
• Tree collars and roots have to be protected. In parking lots cars often deal damage to tree’s stem and roots. The plants have to be adequately protected, by the means of reasonably large borders, or trough specific obstacles in order to prevent the contact between vehicles and tree stems.

 

A SHADED PARKING LOT IS POSSIBLE

Increasing our cities liveability is one of the challenges that awaits us. The benefits generated by green areas have been demonstrated beyond any doubt by the scientific community. Not just parks and garden, but also a tree lined parking lot can help in ameliorating urban microclimate . So it’s also fundamental to spread the knowledge of trees importance for liveability in urban areas, in order to make trees in parking lots common in the asphalt jungle that our cities have become.

Benefits of trees in parking lots is a well known topic in our design experience, as for example in the masterplan of Marinella di Sarzana.