Lilja Timcke
Soil sealing is an anthropogenic soil degradation that threatens not only ecosystems but also humans. Even though the problem is familiar and Switzerland has a strategy to minimize it, during the last few years soil sealing has increased. In order to achieve the SDG Goal 15 “life on land” we have to deal with soil sealing and minimize the consequences.
Soil is an important resource for ecosystems and therefore also for humans but it is threatened by soil changes and uses, for example by anthropogenic soil sealing. Soil sealing happens when an air and watertight cover is placed over the ground and is the most intense use of land we know. It can be found in city and housing areas for example streets, buildings, parking spaces or even terrace slabs (Stettler 2020). The SDG Goal 15 “life on land” wants to achieve a land degradation-neutral world by 2030. This goal emerges as important knowing that soil cannot execute its different functions when degraded. Even worse as soil is a non-renewable resource it can, once destroyed, even act as a self-reinforcing effect which can hinder the fight against climate change.
How is Switzerland dealing with soil sealing?
2018 the sealed area amounted to 2081 km2, which is about two thirds of the inhabitant area in Switzerland and 17.6 km2 soil gets sealed each year. As we can see in Figure 1 the annual level of sealed soil decreased in the period 1997-2009, but it increased in the following period. The strategic plan for soil in Switzerland, the «Bodenstrategie Schweiz», approved by the Federal Administration, wants to achieve the goal to reduce the annual soil consumption to net-zero by 2050 (BAFU 2020).
Figure 70.1 – Annual increase of sealed soil in Switzerland (BFS 2021)
There are different reasons for sealed soil and its increase. The most obvious one is population and economic growth, which leads mostly to an increase in urban areas (Röpke and Lippelt 2014). It seems reasonable that society reacts to the increased demand to build new houses and infrastructure . It is also cheaper to build on unbuilt land as there are little barriers by existing infrastructure above or underground (Deltares 2020). However, soil sealing is found not only in cities and in new housing areas, but also for example in gardens, as it is more convenient to seal the driveway or the garden, so it is easier to take care of (European Commission 2012).
What are possible consequences for ecosystems and humans?
There are various consequences of soil sealing that limits the functions of soil. One of them is heating especially in urban areas. Tar sealed ground has a higher albedo than unsealed ground. This leads to higher absorption of the sunlight which leads to a higher temperature of the air close to the ground. Therefore, rising temperatures can be observed in urban areas, so called urban heating islands. As a consequence of climate change, temperatures are rising on their own and the albedo effect contributes to this increase. These high temperatures change the vegetation and the species composition, as not all species can deal with the changing temperatures. Also, biodiversity is decreasing as sealing destroys the natural habitat for many species. Soils have the potential to store carbon and can thus counteract the greenhouse effect. Through sealing, the exchange between soil and atmosphere is inhibited and the carbon binding capacity gets lower. As a result, sealed soil limits also the soil-atmosphere gas exchange and the lack of carbon fixation contributes to global warming.
Intact soil has the ability to store and filter a lot of water. By putting an impermeable layer over it, soil losses these abilities. As the water cannot drain away, it flows above ground and ends in a water body or canalisation. But this does not solve the problem, on the contrary, it increases the risk of flooding. Sealed soils also have economic consequences, for example the expensive modernisation of the drainage system or even the damages of flooding (Scalenghe and Ajmone Marsan 2008).
What can be done to decrease soil sealing?
Nevertheless, it is unrealistic that we are going back to rocky unsealed roads as sealing is a part of urbanisation. Having sealed ground in some places can be feasible. But still, there are certain ways to minimize the level of sealing and work towards the goal of the Swiss government.
There are several opportunities to reduce or compensate the number of sealed areas. One of them is the approach of the so called green infrastructure. It manages among others the natural water cycle so that water can drain or gets filtered before entering a waterway. The approach to cool down cities is part of green infrastructure. To compensate for the heat in the cities roof greening or the approach of replanting is used, so evapotranspiration can work and cool down urban heating islands.
The best approach would be to unseal areas which do not need to be sealed, for example driveways. But as this is rather expensive and difficult, it is not executed that often. A good alternative to unsealing is the reuse of areas and the development of a city-specific space management, which helps to keep an overview and plans ahead (Röpke and Lippelt 2014). Another approach is to use materials that are not fully impermeable or water-permeable (Figure 2). That way, one can rebuild the connection between the soil and its surroundings and allow soil to fulfil some of its function, which are so important for mankind. Also, thanks to this, the amount of seeped rainwater can be maximized. These water-permeable materials can for example be placed in parking spaces (Europäische Union 2012).
Figure 70.2 – Example of a water-permeable layer, as water can seep away and reaches the soil (Stettler 2020)
In conclusion, we can say that to reach the SDG Goal 15 we have to minimize soil sealing and start to find alternatives or certain management to deal with it. As we can see, there are many ways how to improve the situation today like the use of green infrastructure in cities. A possible problem can be that it is not viewed as urgent in Switzerland and therefore does not get the attention it would need.
References:
BAFU. 2020. “Bodenstrategie Schweiz.” https://www.bafu.admin.ch/bafu/de/home/themen/boden/fachinformationen/massnahmen-fuer-den-bodenschutz/bodenstrategie-schweiz.html
BFS. 2021. Die Bodennutzung in der Schweiz. Resultate der Arealstatistik 2018. Neuchâtel: Bundesamt für Statistik. https://www.bfs.admin.ch/bfs/de/home/statistiken/raum-umwelt/bodennutzung-bedeckung/siedlungsflaechen/versiegelungsgrad.html
Deltares. 2020. “Achieving Land and Soil Related Sustainable Development Goals.” https://ec.europa.eu/environment/soil/pdf/SDG Land BrochureSept2020_EN_v3.pdf
Europäische Union. 2012. Leitlinien für bewährte Praktiken zur Begrenzung, Milderung und Kompensierung der Bodenversiegelung. doi:10.2779/73172
European Commission. 2012. “Soil Sealing.” Science for Environment Policy. In-Depth Report (March):1–41. doi: 10.2779/73172. DG Environment.
Röpke, Luise, and Jana Lippelt. 2014. “Kurz Zum Klima : Bodenversiegelung in Deutschland Und Europa.” 6–9. https://www.econstor.eu/handle/10419/165387
Scalenghe, Riccardo, and Franco Ajmone Marsan. 2008. “The Anthropogenic Sealing of Soils in Urban Areas.” Landscape and Urban Planning 90(1–2):1–10. doi: 10.1016/j.landurbplan.2008.10.011.
Stettler, Sabrina. 2020. “Versiegelung.” Einstein, June 25. https://www.srf.ch/sendungen/me-biodiversitaet/heisse-koepfe-tipps-zum-thema-entsiegelung-der-boeden