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Impervious Soil Coverage 2016

Introduction

The impervious coverage of natural soils by construction and non-porous materials has a multitude of negative effects on the ecosystem, the microclimate in the city and on the human habitat. The effects of impervious coverage are primarily noticeable in cities and metropolitan areas, where a high proportion of the total area is impervious.

Definition

Impervious coverage means the paving of the soil with non-porous materials. The categories of impervious areas are: built-up impervious areas, i.e., buildings of all kinds; and non-built-up impervious areas, i.e., roads, parking lots, paved walkways, etc.

In addition to building complexes and surfaces completely imperviously paved with asphalt or concrete, more porous paving types are also considered impervious, although these often have very different ecological qualities. Such coverings as grass trellis stones or paving stones with wide seams still permit reduced plant growth, are partially permeable to water, and provide for a considerably more favourable microclimate.

The existing types of pavement of non-built-up impervious areas are grouped into four pavement classes, with different effects on the ecosystem (cf. Table 1).

Link to: Vergrößern
Tab. 1: Overview of impervious pavement classes
Image: Umweltatlas Berlin

The Effects of Impervious Coverage on the Ecosystem and the Urban Climate

The complete impervious coverage of the soil causes the irreversible loss of natural soil functions.

Impervious coverage and densification moreover strongly impair the water storage capacity of the soil that is available to plants, as well as its buffering and filtration capacity. Obstructing the water and oxygen supply causes most organisms in the soil to die. Since no more water can seep down, the pollutants entering the soil via air and precipitation are no longer retained in the soil and are partially washed into surface waters. The formation of new groundwater is prevented or reduced.

Impervious coverage of the soil also results in changes in the water balance and the water composition, due to the loss of evaporation and seepage surfaces for precipitation. The rainwater runoff from impervious areas, heavily polluted by tire abrasion, dust, dog excrement, etc., is passed by via the sewage system either directly into the tributaries or into sewage-treatment plants (cf. Map “Management of Rain and Waste Water” (02.09)). The drainage of polluted rainwater after heavy rainfalls often causes the eutrophication of water bodies.

The complete impervious coverage of the soil consequently causes the complete loss of all flora and fauna, but even partial impervious coverage always means habitat loss. Biotopes are fragmented or isolated, while sensitive species are crowded out in favour of more adaptable species.

Pervious soils strongly impact the urban climate due to their capacity to store and supply water to plants. On the one hand, evaporation caused by plants and by the (pervious) soil surface leads to cooling of the air. On the other hand, the air is heated by the high heat-storage capacity of buildings, impervious areas and asphalt streets, contributing to the development of a specific urban climate. Especially in summertime, night-time cooling is reduced (cf. Fig. 1 and the Map “Nocturnal Cooling Rate between 10:00 p.m. and 04:00 a.m.”.

Link to: Vergrößern
Fig. 1: Temperature Range above Various Surfaces (Kessler 1971 in: Mählenhoff 1989)
Image: Kessler 1971 in: Mählenhoff 1989

At the same time, the relative atmospheric humidity too is reduced, since vegetation-covered areas and the evaporation they generate is lacking. This can lead to the occurrence of extreme values which can impair human well-being considerably. In this context, pervious areas, such as parks, play a major role. Parks of even one hectare in size or more have a demonstrably positive climatic effects on human well-being. Vegetation-covered areas also have an effect on the dust and pollutant contents of the air, since, with their large leaf surfaces, they are able to bind dust particles and other air pollutants.

The effects of impervious coverage on the Berlin urban climate are described in detail in various maps of the chapter Climate.

In addition to the above-described consequences for the ecosystem, the degree of impervious coverage in urban areas also has an immediate effect on the human habitat. A high degree of impervious coverage is usually associated with a disparity of open space per capita. Long rows of buildings, frequently interrupted only by asphalt or concrete surfaces, can have a depressing, monotonous effect on residents. Such factors of nature as the change of the seasons can no longer be experienced in the immediate residential environment. Increased dependence on nearby recreation areas at the outskirts of a city on the other hand generates traffic, which also has a negative effect on the environment.

Data on impervious soil coverage is regularly used in important contexts for environmental protection, as well as urban and landscape planning. For example, this data is used and processed particularly often in various models (urban climate, water balance), or evaluating methods, e.g. in soil protection. Furthermore, the documentation indicating how strongly nature and the landscape are impaired by impervious soil coverage is also of great importance. Policy-makers, too, are increasingly requesting regular updates on impervious coverage data at a high chronological resolution, in order to monitor and measure the success of environmental or urban-planning strategies (cf. Reusswig et al. 2016, Klimafolgenmonitoring (Monitoring Climate Impacts) SenStadtUm 2016a).

Methods to Reduce Impervious Coverage and New Land Consumption

Since 2002, the goal of reducing new land consumption to 30 ha per day by 2020 has been formulated in the national sustainability strategy (The Federal Government 2002). Daily new-land-consumption demand in Germany for residential and traffic use currently amounts to 69 ha (2014) (UBA 2016). New land consumption has been reduced in recent years; however, it is still a long way from the target for 2020. Model calculations by the Federal Ministry of Transport, Building and Urban Development predict that new land consumption will level off at around 64 ha per day from 2015 (German Bundestag 2015).

At the UN Summit in New York in September 2015, the 2030 Agenda for Sustainable Development was adopted. The German Sustainability Strategy 2016 (The Federal Government 2016), based on the same, identifies the special need for sustainable soil protection as a resource against the background of increasing urbanization and climate change (Sustainable Development Goal – SDG 15). Working towards the 2030 Agenda goal of a land and soil degradation neutral world, emphasizes the crucial role that soil plays in biodiversity and climate protection (German Sustainability Strategy for Germany, 2016).

Within the framework of the national sustainability strategy, the indicator “new land consumption” was developed for empirical studies and risk assessments examining the consequences of land use. New land consumption is calculated from the daily increase in built-up and traffic areas. This is not equal to the impervious area, since they also include areas which are only slightly impervious (gardens in residential areas, allotments, park facilities or green median strips on roads, etc.). In a conurbation area such as Berlin, however, the increase in built-up and traffic areas is an unsuitable indicator for land consumption (cf. Map “Open Space Development”). For this reason, “soil imperviousness”, which is indicator No 6 of sixteen core indicators for monitoring sustainability, is determined for documenting the economical use of soil as a resource from a sustainability perspective. Environmental Atlas data is also used to illustrate the development of the degree of imperviousness over time (Statistical Office for Berlin-Brandenburg 2014).

In 2005, the Federal-State Cooperative Association for Soil Protection (LABO) appointed a group of federal and state experts to develop a suitable assessment procedure for ascertaining soil impervious coverage at the state level, in order to expand the sustainability indicator “new land consumption for residential and traffic areas” to include the component impervious coverage.

The results of the experts’ group are incorporated into the Environmental-Economic Accounting of the German States (EEAL), and have been documented in the report “Indikator Versiegelung”, (the indicator “Impervious Coverage”) (Frie & Hensel 2007).

LABO reports to the German Conference of Environment Ministers in 2010, 2011 and 2012 document the development of new land consumption and the measures taken by the federal German states to reduce new land consumption. According to the Environmental-Economic Accounting of the German States (EEAL), impervious areas in Germany account for 6.17 % of the total area in 2014. This corresponds to an impervious area of 2.2 million ha. In Berlin, impervious areas cover 34.92 % (approx. 31,140 ha) of the total area in 2015 (Statistical Offices of the German States 2016).

See the Excursus impervious coverage data 2005, 2011 and 2016, which compares the present results with those of the “Indikator Versiegelung” (indicator impervious coverage), by the Environmental-Economic Accounting of the German States (EEAL, Statistical Offices of the German States 2016).

The reduction of land consumption, which is a goal of the national Sustainability Strategy, is to be achieved by space-reduced construction of buildings, densification of inner-city areas, concentration of infrastructure, provision of compensation areas, and the removal of impervious surfaces no longer used (space recycling). With the increase of the quality of the living environment in residential areas, concentrated housing in the city is to be reestablished as an alternative to the “home in the green suburbs” once again. (The Federal Government 2007). Germany’s states and municipalities are to realize these targets in the context of their spatial and construction planning. In March 2017, the amendment of the Building Code was adopted in the course of adapting urban planning laws to the Strategic Environmental Assessment (SEA) Amendment Directive. A key focus is the introduction of a new area category “urban area”, which is to enable a higher level of density of mixed uses while reducing land consumption (German Bundestag 2017).

With the federal soil protection legislation coming into effect, soil including all its functions was protected by uniform nationwide regulations for the very first time. The Soil Protection Law, however, does not provide any direct legal claim, in regard to use changes or land consumption by construction. Generally, the requirement of impervious-coverage removal under Section 5 of the Federal Soil Protection Law (BBodSchG 1998) represents an instrument for areas that are permanently no longer in use to be rendered pervious once again, and thus regain their natural soil functions, as per Section 2 Para. 2 BBodSchG (Oerder 1999). However, since costs and reasonableness are taken into account as additional criteria, this regulation has not proven its worth in practice.

Furthermore, the Federal Building Code (BauGB 2014) and, in some cases, nature conservation legislation comprise pertinent regulations relating to soil as a subject to be protected. These include the so-called soil protection clause according to Section 1a Para. 2 BauGB and the requirement of deconstruction and removal of impervious-coverage according to Section 179 BauGB. With the introduction of the Strategic Environmental Assessment in 2004, logging and describing soil functions became mandatory. As a result, measures to avoid, reduce and compensate for adverse effects must be described and assessed, and planning alternatives must be identified. According to Section 1 Para. 3 No. 2 of the Federal Nature Conservation Act (BNatSchG 2013), soils must be preserved in such a way that they can fulfil their functions within the ecosystem. According to Section 15 Para. 1 and Para. 2 BNatSchG, inevitable interventions in nature and landscape are to be balanced out or compensated.

With a growing impervious coverage in the state of Berlin, there should be a qualitative assessment as to which soils are in use or need of extra protection. The Map “Planning Notes for Soil Protection” (01.13) and the summarized “Catalogue of models and measures for precautionary soil protection in Berlin” (SenStadtUm 2015) serve this purpose.

In its Environmental Report 2016, the German Advisory Council on the Environment demands, among other things, that a duty of review be introduced to determine whether the impervious coverage of an existing area may be removed, whenever a new area is rendered impervious (SRU 2016). In this context, a project is highlighted that systematically records potential areas for the removal of impervious coverage developed by the state of Berlin. As part of nature conservation compensation measures, these areas could then be made available permanently to the ecosystem after the removal of their impervious coverage and the restoration of their soil functions (Map “Potentials for the Removal of Impervious Soil Coverage (Soil De-sealing)”, SenStadtUm 2016).

A further possible instrument for reducing impervious coverage is financial incentives at the individual level. For example, Berlin has since January 1, 2000, invoiced the charge for precipitate-water sewage separately. The introduction of this so-called fee-splitting is based on a ruling by the Federal Administrative Court (resolution of June 12, 1972) and the Superior Administrative Court of Lüneburg (rulings of June 14, 1968 and of April 10, 1980). These rulings stated that in municipalities in which the cost of precipitate-water sewage disposal accounts for more than 15 % of the total costs of sewage disposal, the fees must be invoiced separately. Thus, the fee for precipitate-water sewage disposal is no longer linked proportionally to the general sewage fee, but is rather charged according to the impervious share of the property from which waste water is fed into the sewage system (BWB 1998). Since 2000, owners have therefore endeavoured to keep the impervious area of their property as low as possible, in order to save on sewage fees. Since the new Precipitate-Water Exemption Ordinance of August 2001 came into effect (the Ordinance on Exemption from Requirement for Permission for Harmless Percolation of Precipitate Water – NWFreiV, August 24, 2001), it is possible to obtain proportionate or full exemption from the precipitate-water sewage disposal fee (SenStadt 2001) via measures for relieving the rainwater sewage system via percolation on one’s own property, without permission.