Imperviousness and imperviousness change in Europe

Assessment versions

Published (reviewed and quality assured)

• 25 Mar 2020, 03:11 PM
  - Imperviousness and imperviousness change in Europe

Rationale

Justification for indicator selection

Data and indicators on the extent of, and change in, soil sealing or imperviousness (used synonymously) are important for a number of highly policy relevant issues. Imperviousness is defined as the covering of the soil surface with impervious materials as a result of urban development and infrastructure construction (buildings, constructions and layers of completely or partially impermeable artificial material, e.g. asphalt, metal, glass, plastic or concrete). 

Changes in imperviousness can document land use intensification or land cover/land use change due to urban or industrial development and related increases in traffic infrastructure. All these changes have potentially significant implications for biodiversity, soil functions (including carbon storage and sequestration), hydrological properties, provision of ecosystem services and nature conservation. In particular, exchanges of energy, water and gases are restricted and pressure on adjacent, non-sealed areas is increased. Until recently, the only European dataset available to indirectly document changes in imperviousness was Corine Land Cover (CLC). However, the associated 'land take' indicator covers a lot of surface area that is not actually sealed. The imperviousness indicator supplements this 'land take' indicator by providing information with a higher spatial resolution, based on a more direct measurement of imperviousness and with a shorter update cycle. The following table lists and summarises the datasets/indicators that are available, and helps to select the most relevant product for a specific use-case.

Scientific references

• Assessment of Soil Sealing Management Responses, Strategies, and Targets Toward Ecologically Sustainable Urban Land Use Management Artmann, M., 2014.  AMBIO, 43:530-541. DOI 10.1007/s13280-014-0511-1
• The anthropogenic sealing of soils in urban areas Scalenghe, R. and Marsan, F.A., 2008. Landscape and Urban Planning, V.90, Issues 1-2, p.1-10. DOI: 10.1016/j.landurbplan.2008.10.011
• Soils: Basic Concepts and Future Challenges Bouma, J., 2006. Soil functions and land use. In: G. Certini, R. Scalenghe (Eds.), Cambridge University Press, Cambridge, EU (2006), pp. 211–221
• Urban sprawl in Europe European Environment Agency (2006): Urban Sprawl. The ignored challenge. EEA Report 10/2006. ISSN 1725-9177
• Identification and quantification of the hydrological impacts of imperviousness in urban catchments: A review Jacobson, C.R., 2011. Journal of Environmental Management, Volume 92, Issue 6, 1438-1448. doi:10.1016/j.jenvman.2011.01.018 
• Overview of best practices for limiting soil sealing or mitigating its effects in EU-27 Prokop, G., Jobstmann, H., & Schönbauer, A. (2011). Overview of best practices for limiting soil sealing or mitigating its effects in EU-27. European Communities, 227. Broken link: http://ec.europa.eu/environment/archives/soil/pdf/sealing/Soil%2520sealing%2520-%2520Final%2520Report.pdf
• Progress in Physical Geography: Earth and Environment Sutton, P.C., Anderson, S.J., Elvidge, C.D. (2009) Paving the planet: impervious surface as proxy measure of the human ecological footprint. Progress in Physical Geography. 33: 510-527.
• Place Based Territorially Sensitive and Integrated Approach Zaucha, J. and Świątek, D. (2013), Place Based Territorially Sensitive and Integrated Approach Broken link: http://www.stfk.no/Documents/Nering/Kysten%20er%20klar/Report_place-based_approach_29_03_2013.pdf

Indicator definition

The imperviousness indicator is defined as the yearly average imperviousness change between two reference years, as measured by imperviousness change products. The change is aggregated for a certain reference unit and expressed relative to the size of that unit (as a percentage). The imperviousness change value for a 100 m raster cell is based on 100 m imperviousness change products. The default reference unit is the country, but the indicator can be aggregated based on different spatial units. For example, for a certain country, an imperviousness indicator value of 0.2 %, means that on average, an additional 0.2 % of this country's area has been sealed annually during the period between the two reference years in question. If above a certain rate of increase (threshold values), this value can be used as a warning sign. The aggregation of imperviousness values to reference units is performed using the integrated spatial data platform at EEA.

Units

The unit used for this indicator is the yearly average percentage change in imperviousness relative to the size of the reference unit. It is important to note that the yearly average value is based specifically on the period reported, e.g. 2006-2009, 2009-2012 or 2012-2015, or for the whole time period for which data are available (2006-2015). 

Policy context and targets

Context description

The main policy objective of this indicator is to measure the extent and dynamics (change) of soil sealing, resulting from the development of urban and other artificial land uses.

At the United Nations Conference on Sustainable Development, held in Rio in 2012 (Rio+20), world leaders identified land and soil degradation as a global problem and committed to 'strive to achieve a land degradation neutral world in the context of sustainable development'. At the EU level, the Seventh Environment Action Programme (7th EAP) includes a strong focus on the unsustainable use of land and soil, including explicitly the issue of soil sealing. In this context, the 7th EAP refers to a Commission Staff Working Document with the title 'Guidelines on best practice to limit, mitigate or compensate soil sealing' (SWD/2012/0101).

In addition, land take is explicitly mentioned in chapter 23 of the 7th EAP, stating that:

Every year more than 1 000 km² of land are taken for housing, industry, transport or recreational purposes. Such long-term changes are difficult or costly to reverse, and nearly always involve trade-offs between various social, economic and environmental needs. Environmental considerations including water protection and biodiversity conservation should be integrated into planning decisions relating to land use so that they are made more sustainable, with a view to making progress towards the objective of 'no net land take', by 2050.'

In recognition of the importance of land in safeguarding natural resources, the Commission is considering a Communication on 'land as a resource'.

Other important references can be found in A Sustainable Europe for a Better World: A European Union Strategy for Sustainable Development (COM(2001)264) and the thematic documents related to it, such as the Commission Communication Towards a Thematic Strategy on the Urban Environment (COM(2004)60), Cohesion Policy and Cities: the urban contribution to growth and jobs in the regions (COM(2006)385), Europe 2020 (COM(2010)2020), general provisions on the European Regional Development Fund, the European Social Fund and the Cohesion Fund Council Regulation (EC) No 1083/2006, as well as the concept of territorial cohesion.

Targets

Although there are no quantitative targets for soil sealing/imperviousness at European level, different documents reflect the need for better planning to control urban growth and the extension of infrastructures. Policies relating explicitly to land use issues, and especially physical and spatial planning, have, until now, generally been the responsibility of the authorities in Member States. The European Commission's Roadmap to a Resource Efficient Europe (COM(2011) 571) introduces, for the first time, a 'no net land take by 2050' initiative that would imply that all new urbanisation will either occur on brownfields or that any new land take will need to be compensated by reclaiming artificial land.

European policy, although it has no spatial planning responsibility, sets the framing conditions for planning. At the European level, the 1999 European Spatial Development Perspective (ESDP), a non-binding framework that aims to coordinate various European regional policy impacts, already advocates the development of a sustainable, polycentric and balanced urban system with compact cities and a strengthening of the partnerships between urban and rural areas, as well as parity of access to infrastructure and knowledge, and wise management of natural areas and cultural heritage. The 2008 Green Paper on territorial cohesion, and the 2007 EU Territorial Agenda and Action Plan by the Territorial Agenda of the EU and the Action programme for its implementation (COPTA, 2007) build further on the ESDP. Specific, relevant actions in the field of 'Land', in particular are Action 2.1d 'Urban sprawl' and Action 2.2 'Territorial impact of EU policies'.

Demand for new urban areas may be partly satisfied by brownfield remediation. Its environmental advantages are clear: relieving pressure on rural areas and greenfield sites, reducing pollution costs, more efficient energy use and natural resource consumption, facilitating economic diversification and emerging habitat (housing) requirements. Europe has several examples of regional strategies for economic regeneration and brownfield development (The OECD Territorial Outlook 2001). On average, land recycling increased steadily between 1990 and 2012 on an annual basis, with considerable variation between countries, and within countries. Stronger links between EU urban and soil policies could encourage this further (e.g. following up respective 6th EAP Thematic strategies).

Related policy documents

• COM(2010) 2020 final, Europe 2020: A strategy for smart, sustainable and inclusive growth
  European Commission, 2010. Europe 2020: A strategy for smart, sustainable and inclusive growth. COM(2010) 2020 final. 
• European Spatial Development Perspective (ESDP)
  European Spatial Development Perspective (ESDP). Towards Balanced and Sustainable Development of the Territory of the European Union. Informal Council of Ministers responsible for Spatial Planning in Potsdam, May 1999.
• General Union Environment Action Programme to 2020 - Living well, within the limits of the planet
  7th EAP. ISBN 978-92-79-34724-5 doi:10.2779/66315
• Guidelines on best practice to limit, mitigate or compensate soil sealing
  Commission Staff Working Document SWD (2012) 101
• Roadmap to a Resource Efficient Europe COM(2011) 571
  Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions. Roadmap to a Resource Efficient Europe.  COM(2011) 571  

Methodology

Methodology for indicator calculation

• The 100 m imperviousness change product, produced as a deliverable in the 2009, 2012 and 2015 updates, is the basis for this indicator. 
• Previous versions of this indicator were published separately for the 2006-2009 and 2009-2012 periods. However, improved production workflows and products, and challenges in comparing the results for the reference years, made it necessary to fully re-process the 2006-2009 and 2009-2012 change products as part of the production for the 2015 reference year. Therefore this update of the indicator uses the new and improved full time series of 2006-2009-2012-2015. Errors in previously published change products were corrected, and the new time series fully replaces any previously published versions.
• Although imperviousness changes included in the 100 m change product could be summarised directly as certain reference units, the calculation of the indicator is performed by ingesting 100 m imperviousness change values into the EEA spatial data platform in order to create harmonised results with other spatial indicators using a similar methodology. The data cube approach used for the data platform enables the extraction of statistics based on a system of grid-cells with a 1 km side length (an area of 100 ha). 
• Reference units, such as countries, NUTS3 regions etc. are already included in the cube as so called 'dimensions' and are used for the statistical aggregation of imperviousness changes corresponding to required reference units.
• Yearly average imperviousness change values are calculated by dividing the average imperviousness change values by the number of years between two status years.

Methodology for gap filling

• Known gaps were caused by image gaps (missing input Earth observation data) in both 2006 and 2009 data. For 2009 gaps, the available 2006 values were used for the 2009 status layer and gaps in 2012 image data were filled with imperviousness data from 2009. This means that in some areas (under image gaps), the real sealing change is not known for 2009 and 2012, and some under-estimation of the real sealing increase (for those areas) is likely (because data from previous reference years are used). This practice of gap-filling with previous reference year data was discontinued for the 2015 (and future) updates, but it was not possible to fully eliminate the effects from the 2009 and 2012 datasets. 

Methodology references

No methodology references available.

Data specifications

EEA data references

• Copernicus aggregated Imperviousness change information 2009-2012 provided by European Environment Agency (EEA)
• Copernicus Land Monitoring Service - High Resolution Layers - Imperviousness provided by European Union

Data sources in latest figures

Uncertainties

Methodology uncertainty

• The methodology for deriving the indicator is simple and introduces very little uncertainty. However, it needs to be fully understood that the yearly averages are only valid for the 3-year reference period under consideration. Possible variation within the 3-year period (for individual years) is currently not captured.

Data sets uncertainty

• This indicator is based directly on the mapping of soil sealing/imperviousness using Earth observation data of about 20 m spatial resolution (moving to 10 m from the 2018 reference year onwards). Real sealing will differ from the values derived in this way for various reasons:
  
  
  • The spatial resolution of the input imagery means that very small sealed surfaces will sometimes not be captured, e.g. small buildings and small paved roads, and other sealed surfaces with a very small footprint. This can lead to an underestimation of real sealing. It is expected that this issue will become less relevant as we move to 10 m spatial resolution products from the 2018 reference year onwards.
  • As with all Earth observation derived products, the data contain omission errors (sealed surfaces not detected) and commission errors (areas wrongly classified as sealed). The distribution of these errors depends on the quality of the input data, calibration during production and local differences in spectral contrast (which makes sealing in some locations 'easier' to detect than in other locations, depending on the context).
  • The 2015 production included a full re-processing of previous reference years and change products. Therefore the current 2015 product, and the latest versions of 2006-2009-2012 products fully replace the previous datasets. For the same reasons, this indicator update replaces all previous published imperiousness indicators. 
  • For imperviousness/soil sealing products, the term 'reference year' must currently be understood to comprise a maximum of 3 years (the year before the reference year, the actual reference year, and the year after the reference year for gap-filling). This means that the Earth observation data used to produce the '2009 reference year' are, in reality, a mix of 2008, 2009 and 2010 acquisitions. Due to radical improvements in image availability with the Sentinel Satellites, this situation already significantly improved for the 2015 reference year, and will further improve for the 2018 reference year (where the imagery is fully from the 2018 reference year).

Rationale uncertainty

No uncertainty has been specified