A suburban forest can provide shelter during hot weather, but that's not all. Green areas also help cool the cities themselves – that's the conclusion reached by scientists who analyzed data for 30 Chinese cities over 20 years. The data confirms that this reduces the urban heat island effect.
The fact that streets without greenery and concrete squares intensify the heat in the city is easy to feel on your own skin. But these effects are also visible on a larger scale. Heating, impermeable surfaces lead to the urban heat island effect. On the same day, in the same weather, the city can be much hotter than the neighboring rural or forest area.
This effect is particularly visible at night, when heated concrete and asphalt release their accumulated heat. This translates into our comfort and health. The heat can be dangerous for the elderly, children or the chronically ill. The effects of heat accumulate when it lasts for many days. And hot nights – associated with the urban heat island – do not allow our bodies to regenerate, can make it difficult to sleep, which has measurable effects on health.
It is known that greenery in cities can help to mitigate this effect. Trees, parks, green areas, meadows and greenery on the streets provide shade, protect against heating and lower the temperature. But do green areas outside borders cities can also have an impact? Scientists decided to find out – and the results are promising.
Rings of green against the heat
– We often focus on how green spaces, wetlands or waterways can cool cities. But urban land is precious and hard to find space for. We have shown how land use outside the city can have a big impact on the temperature in the city centre – he said Prof. Shi-Jie Cao, one of the authors of the study.
The results of the work of the team of scientists were published in July in a scientific journal “Nature“. They show that green rings around cities have an impact on the temperature in the urbanized areas themselves.
This is because the urban heat island creates a local low pressure zone. This “sucks” air from the city's surroundings. If there are rural areas, forests or lakes around it, the air is cooler and the temperature in the city center is lowered. Forests and large lakes work particularly well. Green rings can lower the average temperature by 0.5 degrees Celsius. Although it may not sound like much, in combination with the use of greenery inside cities, it can make the difference between heatone that only causes discomfort and one that is dangerous to health.
The study showed that the relatively close proximity of green areas to the city limits (up to 10-15 km) and their quality are important. – Overheating of the city can be alleviated to a greater extent by connecting rural areas, planting more forests scattered throughout the city, and having fewer, larger lakes instead of many small reservoirs – recommends Prof. Shi-Jie Cao.
What about forests around cities?
IN Polish cities with greenery around cities are different. For example, Warsaw has forest complexes to the east and south, Kampinos National Park to the north-west, and the Vistula River flowing through the center. Bydgoszcz is surrounded by forests, but Wrocław, for example, has much less forest areas near the city limits.
The Ministry of Climate and Environment initiated this year the process of creating social forests around 13 large cities and metropolises. In August, teams will begin work, including foresters and non-governmental organizations, to develop specific recommendations and designate areas for new social forests. In such forests, cutting down trees for timber is to be severely limited or stopped, and the social functions of the forest will be in the foreground. The Ministry promises that we will learn about specific locations this year.
– These forests are to play an important role in terms of recreation, contact with nature, but also to develop the idea of green rings around large cities – said Deputy Minister Mikołaj Dorożała.
You can read more about the process of creating social forests in this article: The designation of social forests begins. The Ministry has shown maps