Urban pans – or about impervious surfaces in cities

o powierzchniach nieprzepuszczalnych

There is one prevailing trend in urbanization worldwide and in Poland – its growth. The benefits of living in the city are attracting more and more people. Urban tissue is growing and densifying – but is it in the right way?

The urgent need to unseal impervious spaces is still overlooked in most Polish cities. There is no appreciation of urban greenery, water retention or the woodlands surrounding the city. In recent years, temperatures, especially during the holiday months, have been downright unbearable for city dwellers. There has even been a term that concreted surfaces heat up like pans. Many people began to measure the temperature near the surface of the ground – on playgrounds, sidewalks – and the results were dismal. In places, they exceeded 60°C, when at the same time the sun-warmed lawns reached only half that value.

It’s not just the hot weather that urban residents are finding increasingly troublesome. It should not be forgotten that as a result of sealing the surface, there is rapid runoff of rainwater. This is of great importance in case of heavy rains. The city’s sewer system can’t keep up with draining water, and it happens that streets or squares are flooded and completely impassable.

Thus, it can be concluded that the inappropriate direction of urban fabric development and the intensification of extreme phenomena associated with climate change have dire consequences for urban residents. We are no longer just talking about discomfort, but a threat to the health and lives of residents.

Good to know: impervious surfaces have a high rate of heat accumulation and low heat capacity relative to water and green areas. Elements built of materials such as concrete, brick and asphalt absorb much more sunlight than they will reflect, to further give off accumulated energy and thus increase ambient temperatures [1] .

Cities can check how tightly concreted they are

Late last year, the Ministry of Climate and Environment’s website published a Guide for Cities, which divides nature-climate indicators into four categories:

  • Greenery and urban retention;
  • Impervious surfaces (concreted);
  • Urban heat island;
  • Biodiversity.

In addition, the guide describes how to calculate indicator values using free data. Downloadable materials can be found on the Ministry’s website.

In the category of Impervious surfaces (concreted), two indicators are presented:

  • The share of impervious surfaces in the urbanized area of the city;
  • Impervious surfaces in the city per capita.

The first reports the share of impervious surfaces in the urbanized area of the city. We include compact and loose housing, industrial, commercial and transportation areas. Data from satellite images of the CORINE Land Cover (CLC) project are used to delineate urbanized areas.

The second indicator provides knowledge about the area of impervious areas in the city per capita. The main source of information needed for the calculations is BDOT10k, a database containing the spatial location of topographic objects along with their basic descriptive characteristics. It is available for download on the national geoportal website. The components that together form impervious surfaces in a city are buildings, roads, pedestrian and bicycle paths, plazas or airports. The material of the pavement plays an important role in this case.

Example of Knurów, a city in the Silesian province

For a better illustration and understanding of the indicators, they were recalculated and presented graphically using the example of Knurów. It is a city located in Silesia Province, Gliwice County. Its area is 34 square kilometers and in 2022. was inhabited by 36,044 people[2]. Urbanized areas, delineated based on CLC data (Corine Land Cover 2018), cover 11 square kilometers. Impervious surfaces, calculated from satellite imagery, cover 3.22 square kilometers, so their share of the city’s urbanized area is 29.3%. On the basis of BDOT data (Database of Topographic Objects), it was calculated that impervious surfaces in the entire city occupy 3,056,762.2m2, in which case there is 84.8m2 of impervious surfaces per 1 resident of the city of Knurów.

wodne sprawy 5 2023 5
Images showing the distribution of impervious surfaces determined from various methods and databases
Wyk: Monika Mazur, Pectore-Eco, based on: Corine Land Cover 2018, BDOT, GUGiK data.

The indicators discussed above provide information on the degree of sealing in the city, and also indicate where this phenomenon may occur in the future. The results and depictions obtained can help in the sustainable planning of spatial activities. Urban sprawl is an extremely important aspect of urban adaptation to climate change.

What can we do?

There are many ways to reduce concreted areas. In addition to setting aside space in the garden for a lawn, flowerbeds or a pond, it is also important to choose the right materials, such as forgoing traditional paving stones. In cities, it is a good idea to be active in neighborhood councils and promote the use of modern material solutions, such as green parking lots and micro-retention areas – rain fields or absorption wells. You can also take advantage of the opportunity to implement projects through the civic budget and propose the creation of a rain garden, green bus stops or increased tree plantings, such as in playgrounds.

In the article, I used, among others. From the works:

[1] Cities in the face of climate change. IRMiR, Warsaw-Krakow, 2020

[2] Local Data Bank: https://bdl.stat.gov.pl/BDL/

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