Assessment and Reporting on Soil Erosion
This report presents the results of a peer review of work on soil erosion carried out by the EEA up until 2001. It also summarises the conclusions of an expert workshop on indicators for soil erosion, held in Copenhagen in March 2001.
This report has been prepared by the
Katholieke Universiteit Leuven under
contract to the European Environment
Agency (EEA) and is the final result of a
working group on indicators for soil erosion.
The working group was established by the EEA in order to progress with the work on soil in the interim period before the new European Topic Centre on Terrestrial Environment (ETC/TE) started in July 2001. In 2001 the EEA carried out a peer review of its work on soil, with particular reference to the development of policy-relevant indicators and the identification of probable problem areas for soil degradation (‘hot spots’) (1).
The review was in particular focused on work on indicators for soil erosion and soil sealing, and two associated technical workshops were held in March 2001 to facilitate this review. This report provides the background on and analyses the work done by the EEA on soil erosion in the period to 2001 and summarises the conclusions of the workshop on indicators for soil erosion, held in Copenhagen on 27–28 March 2001.
The purpose of the workshop was to identify a set of recommendations concerning reporting on soil erosion (as part of the wider theme of soil degradation) that could then be considered for inclusion in the work programme for the new ETC on Terrestrial Environment.
Soil erosion is a natural process, occurring over geological time. Most concerns about erosion are related to accelerated erosion, where the natural rate has been significantly increased by human activities such as changes in land cover and management. This report focuses on accelerated erosion caused by water.
Runoff is the most important direct pressure of severe soil erosion. Processes that influence runoff must therefore play an important role in any analysis of soil erosion intensity, and measures that reduce runoff are critical to effective soil conservation. In Europe, soil erosion is caused mainly by water and, to a lesser extent, by wind. In the Mediterranean region, water erosion results from intense seasonal rainfall on often fragile soils located on steep slopes. The area affected by erosion in northern Europe is more restricted and moderate rates of water erosion result from less intense rainfalls falling on saturated, easily erodible soils.
According to the Glasod assessment, in Europe, excluding the Russian Federation, about 114 million ha or more than 17 % of the total land area is affected by soil erosion, of which more than 24 million ha or approximately 4 % show high or extreme degradation and nearly 70 million ha or 11 % are affected by moderate degradation. The various regions of Europe show different patterns, for example in the EU and EFTA countries the area subjected to soil erosion is about 9 % of the total land area. It increases to 26 % in the candidate countries and to 32 % in the rest of Europe (excluding the Russian Federation). However, these findings are based on fragmented and nonstandardised information and hence may not be consistent.
Soil erosion: a priority at the European level
In April 2002, the European Commission adopted a communication on soil protection, endorsed by the Council of Ministers in June 2002. The communication considers soil erosion as one of the major threats to Europe’s soils and a priority for action. Increasing the awareness amongst scientists and policy-makers about the problem of soil degradation through erosion in Europe is now an urgent requirement. The identification of areas that are vulnerable to soil erosion can be helpful for improving our knowledge about the extent of the areas affected and, ultimately, for developing measures to keep the problem under control.
In a long-term perspective, the
implementation of the work on indicators
discussed in this report should certainly
contribute to improving the information
basis needed to prepare, implement and
monitor a sound European strategy on soil, in line with the priorities set down in the sixth environmental action programme (EAP) and the communication on soil protection.
Policy-relevant indicators on soil erosion
Objective and measurable criteria with
potential to compare between areas and
monitor changes over time are needed to
describe the condition and management of
soil erosion. The driving forces–pressure–
state–impact and responses (DPSIR)
assessment framework in combination with
the multi-function and multi-impact (MF-MI)
approach provides a methodology for the
integrated assessment of the soil environment, enabling the inclusion of cause–effect relationships into policy-relevant indicators. The application of the DPSIR assessment framework to soil erosion is
discussed in this report.
Following the DPSIR assessment framework,
a set of soil erosion indicators have been
proposed by the EEA and are reviewed in
Part I of this report. A major difficulty in the
development of these indicators is availability
of data. The proposed pressure indicators
link to the driving force ‘agricultural
intensification’ and all have in common that
they are complex and not directly linked to
the phenomenon of soil erosion. The identified indicators of state and impact are difficult or expensive to measure and the data are usually not readily available.
Indicators of response are prevention and
control measures, which are rarely in place at
Land cover/use and management are the
most important factors that influence soil
erosion. Some of the indicators proposed are related to land use. These can be regarded as a basis for assessing pressures that may result in soil erosion but they require further analysis and inclusion of other factors. Human activities that affect land use and determine land use intensity include agriculture, infrastructure, recreation, mining activities or forest management. It is therefore recommended that regularly updated Corine land cover data are used in combination with earth observation derived products such as the normalised difference vegetation index (NDVI) in order to capture seasonal variations in land cover. Existing policies for the protection of soils and the degree of enforcement of such policies should also be monitored.
Regional soil erosion assessment is needed on a European scale in order to make objective comparisons that may provide a basis for further environmental analysis, economic statements or policy development. Some methods for carrying out regional assessments are based on the collection of distributed field observations, others on an assessment of factors, and combinations of factors, which influence erosion rates, and others primarily on a modelling approach.
None of the reviewed methods presents stateof- the-art regional soil erosion assessments. The Glasod and hot-spot maps can be classified as methods based on distributed point data, while the RIVM and Corine maps can be classified as factor- or indicator-based maps. Other current developments are model-based risk analysis, such as Pesera.
At the workshop the following topics were discussed: assessment and reporting framework; regional and spatial assessment methods for soil erosion and data availability; and indicators for soil erosion. Indicators should be developed according to the following properties and procedures: quantitative, objectively calculated, validated against measurements and evaluated by experts.
The formulation of suitable remediation measures and mitigation strategies requires a regional assessment of soil erosion; the extent and magnitude of areas at risk is essential to prepare soil conservation policies. The method should combine all four strategies of regional erosion assessment, i.e. measured data, expert mapping, factor (thematic) mapping and regional modelling. Factor- and model-based approaches offer the advantages of repeatability and transparency. However, the results need to be validated against measurements and evaluated by experts so that the models or factor approaches can be adapted to reflect the reality.
A set of specific recommendations for the EEA and ETC/TE was developed with the purpose to contribute to the EEA work programme and to the discussion at the European level. These recommendations are related to the general reporting and networking mechanism, to the DPSIR assessment framework, to the proposed indicators by the EEA, to the explicit incorporation of land use into soil erosion indicators, and to the implementation of regional erosion assessments.
In particular, since soil erosion has impacts on several media, such as water quality, working links should be developed with other ETCs and specifically with the ETC on Water. Links with other international initiatives and with data providers should also be maintained.
A revised scheme for soil erosion within the DPSIR assessment framework is proposed. It is advised to better explore the dynamics of the factors involved in this scheme and to undertake a stakeholder analysis on the proposed scheme.
The area affected by erosion is an important indicator for the state of soil erosion, and should be complemented with an indication of the magnitude of erosion in particular areas. Actual soil erosion measurements, such as those collected for the hot-spot map, should continue to be compiled. However, the difficulty of making truly objective comparisons between, and often within, areas calls for a standardised approach to record and particularly map the observations.
Therefore, a Europe-wide monitoring network for soil such as proposed by the EEA (2001b) should include monitoring of soil erosion.
A regional assessment using modelling, expert estimates and other methods should be developed in order to provide a general view and identify the hot-spot areas where a detailed soil erosion monitoring programme should be undertaken.
The temporal and spatial patchiness of soil erosion favours a risk analysis approach in order to make comparisons between regions and to complement field measurements and observations. Modelling efforts should be thoroughly validated against erosion measurements, and a clear distinction should be made between modelled erosion risk and present-day erosion rates. A programme to monitor soil erosion across different agroecological regions and under different land uses should underpin both mapping exercises and regional soil erosion risk assessment methods. Only then a sound approach is ensured of estimations and mapping features that are directly validated and compared with measurements.
Moreover, measuring campaigns may lead to new insights and therefore to both better mapping and risk assessments.