The term "sealed area" is used when land is covered with practically impermeable materials, e.g. for the purpose of constructing buildings or roads. It can result in soil no longer absorbing rainfall, producing biomass, or binding CO2 as a storage and filter medium. It is in principle possible to restore a sealed area of land by removing the material and structures, but this process normally damages the basic ecological functions of the soil to such an extent that restoring the land to its original state is not possible over the medium term.
The total sealed area in Switzerland has increased significantly since 1979/85 with every series of data collected for land use statistics (15.7% between 1979/85 and 1992/97; 11.6% between 1992/97 and 2004/09). The sealed area in 2004/09 totalled 1,920 km2, which is 4.7% of the country's entire surface area.
Clear differences can be observed within the 5 main regions of Switzerland. The sealed area was 214 km2 in the Jura region, 1,111 km2 in the Central Plateau, 335 km2 in the Northern Alps, 156 km2 in the Central Alps and 101 km2 in the Southern Alps. The lowest proportion of sealed land is in the Central Alps. The degree of sealing in the Southern and Northern Alps is about twice as high as in the Central Alps. In the Jura region, the development rate is around three times that of the Central Alps. By far the highest rate of land sealing is in the Central Plateau, where it is six times higher than that of the Central Alps.
Urbanisation and increasing mobility are the most important factors in the constant increase in land sealing. Growing demand for living space explains the large increase up to around 2000, while intensive population growth explains the post-2000 situation.
Preliminary results from efforts to promote denser living can be observed since the increase in area covered by residential buildings after 2000 is essentially still explained by the increase in population, but not by greater demand for living space.
Furthermore, the increase in the sealed area slackened slightly between 1992/97 and 2004/09 (still 11.6% compared to 15.7% 1992/97). At a few sites in Switzerland, buildings and structures are being removed from sealed land, while major efforts are being made to improve settlement ecology through roof greening and unsealing in order to mitigate certain negative ecological impacts.
Copernicus Land Monitoring Services provides the "impervious area layer“, which is updated every 3 years for all of Europe (2006, 2009, 2012). The data are currently being thoroughly checked to see how consistent they are with terrestrial data sources. The sealed area is not an indicator in the European indicator system. Systematic reference values are still not available. Germany reported a sealed area of 6.1% of its surface area in 2010 (http://www.stadtentwicklung.berlin.de/umwelt/umweltatlas/edc102_01.htm). Switzerland's sealed area is significantly lower at 4.7%.
The collection of data for this indicator is based on the land use statistics for Switzerland. Of the 27 different basic land cover categories in the land use statistics (NOLC04), 3 can be used to assess sealed areas, particularly categories 11 (paved areas), 12 (buildings), 13 (greenhouses). Category 11 also includes partially sealed areas, such as gravelly soil. The surveying interval for zone statistics is 12 years, which means that short-term changes in sealed areas are not ascertainable. The statistics are based on random sampling. Surveys and evaluations were carried out between 1979 and 1985 for the first set of land use statistics, between 1992 and 1997 for the second set, while the third set used data from the years 2004 and 2009. The fourth survey based on aerial photos has been underway since 2010, and results for the entire country of Switzerland will be available by 2022.