Cluster Soil | Umweltbundesamt

On the relevance of the action field

Soils fulfil diverse tasks that are important for ecosystems and human beings. They provide biotopes and habitats where plants, animals and microorganisms live. In particular soils that are nutrient-poor, very wet or very dry, harbour rare species communities worth conserving. It is also true that soils are per se highly complex ecosystems. The amount of living organisms in just a handful of soil easily outnumbers the world’s entire human population. In a landscape’s water balance, soils play a preeminent role, as they store and filter water in considerable quantities. This makes them natural buffers warding off drought and floodwater hazards while providing us with clean groundwater. Fertile soils are essential for successful agricultural production. Likewise, healthy soils are a basic requirement for producing healthy victuals. In Germany, all these important soil functions have been protected by law since 1999 when the Federal Soil Protection Act (BBodSchG) was passed. Climate change influences the soil properties, and consequently also the soil’s diverse uses. Furthermore, there are interactions with challenges posed by climate change, given that soils are the foremost terrestrial carbon sink on earth. At the global scale, soils currently store roughly 1,460 billion tonnes of carbon. Hence, there is an equally high risk that – when destroyed or used unsustainably – soils become sources of CO₂ emissions. As climate change progresses, with dry and wet periods becoming more frequent and intensifying, it follows that the soils’ role as a buffer for water balance is gaining more and more importance.

There are numerous interfaces between the DAS ‘soil’ action field with other DAS action fields, such as ‘Agriculture’, ‘Woodland and Forestry’ as well as ‘Water balance and water management’ which are referenced below.

DAS Monitoring –what is happening due to climate change

The climate influences numerous soil processes including a soil’s formation, its properties and its functions. Soil processes such as weathering, formation of minerals, decomposition, development of humus and structure are strongly dependent on temperatures and availability of water. The diversity of soils is great, and just as diverse are the impacts of climate change.

Where climate change alters precipitation and temperature regimes, this in turn has a direct influence on the water balance of the soils (cf. Indicators BO-I-1 and BO-I-2), the replenishment of groundwater (cf. Indicator WW-I-2) and the temperature scenario (cf. Indicator BO-I-4) in the soils affected. Consequently, the mineral balance will also change. Changes in the soil are bound to affect the type of soil utilisation. Any restrictions regarding the availability of soil water will lead to yield losses in agriculture (cf. Indicator LW-I-2) and to deterioration of forest condition (cf. Indicator FW-I-3); under extreme conditions, such restrictions can also result in more damaged timber accruing in a forestry context (cf. Indicator FW-I-5).

Too much water also has adverse effects on soils. Moreover, more frequent and more violent heavy rain events can favour erosion (cf. Indicator BO-I-3). Such developments in turn lead to a loss of soil fertility and a decrease in water retention and material storage capacity as typically, this results in the topsoil – rich in humus and nutrients – being removed. Once soils become unable to absorb major volumes of precipitation, this will favour the formation of floodwater (cf. Indicator WW-I-4) along with all its associated consequences.

Future climate risks – outcomes of KWRA

According to the 2021 Climate Impact and Risk Analysis (KWRA), the risk of soil erosion by water or wind and the risk threatening the productive function of soils were estimated to become high as soon as the middle of this century. Tied in closely with this, the risks to soil biology, the balance of soil matter and consequently soil fertility, were estimated to become medium by the middle of the century.

By contrast, a medium risk for a change in the soils’ filtration and buffering functions is not expected to arise until the end of the century. With a view to the soil water regime, the 2021 KWRA analysis has depicted the following risks: The increase in summer droughts will in future lead to lower seep rates at that time of year. Heavy rain events in summer frequently do not contribute to the formation of seep owing to precipitation running off the surface. Against this background, the replenishment of groundwater occurs predominantly in late autumn and winter, in other words, outside the growth period. This fact increases the risk that inadvertently, the seep transports unused nutrients down into the aquifer. A high risk of water shortages in the soil and a change regarding seep is expected to arise as early as the mid-century. Waterlogging and more frequent landslides and mudslides are regarded as a medium risk expected to arise by the middle of the century. In assessing the climate risks for the soil action field, the low certainties mentioned almost throughout the 2021 KWRA analysis were adopted for this action field. Particularly low is the certainty in respect of assessing the soil biology. Substantial research would be required to permit making any statements regarding soil biology on a technically reliable basis. Somewhat higher, that is to say medium (within a scale of low- medium – high) is the certainty in assessing soil erosion.

Where do we have gaps in data and knowledge?

Compared to the previous – 2019 – Monitoring Report, the indicator set used in the present – 2023 – Monitoring Report, has been extended and further expanded in terms of contents. Nevertheless, as in the past, it has not been possible to incorporate indicators for certain relevant themes.

As far as the case study on soil erosion is concerned – illustrated in the 2015 and 2019 Monitoring Reports – it was possible to develop the 2023 Monitoring Report further, so that the illustrations apply nationwide. However, as before, it was possible to illustrate the erosion risk only in terms of rainfall erosivity (R-factor). In respect of other effects of climate change influencing the erosion scenario, such as changes in management procedures, the spectrum of crop species or the seasonal distribution of erosive precipitation, this indicator does not permit making any statements. So far, there is no contiguously representative erosion monitoring available, owing to the costs and also the fact that consistently numerous (methodological) issues remain unresolved in Germany. It is, above all, the extreme variability in terms of space and time regarding the erosion scenario, that makes representative surveys difficult. Wind erosion has so far not been included as a theme in the Monitoring Report. Moreover, there are some major uncertainties regarding the potential relationships with climate change. While it is true that, as climate change progresses, the dry condition of topsoils has come to exist more and more frequently, any wind-related projections are still fraught with uncertainty.

Soil biology is influenced significantly by temperature, water balance and soil carbon. It is therefore assumed that – in terms of biological activity – there is a close connection between the composition of soil flora or fauna and climate change. However, the complexity of relationships and influences of land use and land management is high. Hence, it has not been possible to date to propose any suitable indicators. Within the framework of a UBA project and with a view to the new European Soil Monitoring Law, soil-related indicators are currently being developed for the purpose of reporting on climate adaptation and climate protection. In this context, a particular focus is dedicated to soil biology. It is true to say that there is a DAS Monitoring indicator (cf. Indicator BO-I-1). However, that indicator is based on model-derived data. The indicator referring to soil water in forest soils (cf. Indicator BO-I-2) is just a case study. There is a problem insofar as the data collection surveys conducted in the Länder of the Federal Republic have so far not been harmonised sufficiently. So far, climate-change related alterations in the material balance of soils have not yet been covered as a theme in DAS Monitoring. It is important to note that, apart from climate change – especially in respect of soils used for agricultural and forestry purposes – there are many other influential factors. Hence, it has not been possible so far, to establish any straight-forward causal relationships. Without the benefit of some additional scientific insights, the development of meaningful indicators remains impossible.

As before, it is still a major challenge to assess soil data at the nationwide scale. Although there are several nationwide observation programmes such as the Soil Monitoring Sites (BDF) and the Soil Condition Survey for Forestry and Agriculture (BZE), the sampling and analytical methods employed in the Länder still differ despite efforts towards harmonisation. This is because the Länder are keen on maintaining, as much as possible, the stability of their time-series related surveys. Against the background of the problematic data situation, the UBA commissioned several research projects in recent years, with the aim to check the availability of soil-related data for nationwide descriptions of soil condition and any associated changes. As a result, a concept was presented in 2022 in respect of a working group (Klimafolgen-Bodenmonitoring- Verbund) with the remit to lay the foundations for establishing a centre for monitoring soil in terms of climate change impacts nationwide. This is intended to consolidate expertise in the field of soil issues across different government departments, and to ensure that national and international reporting obligations regarding soil can be met in the future with nationally harmonised, quality-assured soil information. In parallel with setting up the soil monitoring centre, work is ongoing regarding the further development of nationwide indicators.

What’s being done – some examples

In terms of surface area, agriculture constitutes the most widespread intervention in natural soil structures, because more than half of Germany’s surface terrain is used agriculturally. As far as strengthening the resilience of soils is concerned, agriculture therefore plays a key role. In terms of adapting the agricultural use of soil, agricultural funding support is an important lever. With the ‘Greening’ of the European Direct Payments Regulation, which was in force from 2014 to 2022, support for agricultural enterprises under the Common Agricultural Policy (CAP) was made conditional on those enterprises having to contribute to environmental and climate protection. The Greening stipulations were also used to promote soil protection measures, such as the cultivation of catch crops. The previous Greening stipulations and the general ‘Cross Compliance’ obligations were consolidated to form the new ‘conditionality’ as of 2023. This new conditionality is now composed of two parts – the Statutory Management Requirements (GAB) and the compliance with standards for the maintenance of good agricultural and ecological condition (GLÖZ Standards). GLÖZ, on the other hand, encompasses further and, in part, stricter measures which, among other things, are intended to improve soil protection and the resilience of soils. Part of this is, for instance, the conservation of permanent grassland (cf. Indicator BO-R-2) and the safeguarding of minimum soil cover at the most sensitive times of the year, which includes the cultivation of catch crops. Both measures provide, above all, protection from erosion while also supporting humus production (cf. Indicator BO-R-1). Moreover, the EU member states are obliged, under the new CAP funding period, to voluntarily provide eco-regulations (ER); any beneficiary of this funding must invest part of their direct payments in these measures. The ER catalogue also includes measures intended to improve soil protection while contributing to climate change adaptation.

In principle, forests (including woodlands) are regarded as a soil-protecting type of use. On sites that are particularly at risk from erosion or from becoming overgrown, forests can be designated as soil protection woodlands or forests in order to safeguard permanent soil cover as well as root penetration. That notwithstanding, soil protection is ascribed increasing importance in respect of forest cultivation. The funding programme ‘Climate-adapted Forest management’ launched in 2022 by the BMEL also provides funding for measures targeting soil protection. This includes providing greater skid trail spacings to limit soil compaction, as well as forest enhancement by means of deadwood for humic enrichment (cf. Indicator FW-R-3). Soils can fulfil their important functions – in terms of ecosystems and in the interest of adaptation to climate change such as water storage and landscape cooling – only provided they are protected from overbuilding and sealing of surfaces (cf. Indicator RO-R-5). This is the reason why a reduction in land use conversion is not just a core sustainability objective, but also an objective pertaining to climate change adaptation. The German Sustainability Strategy updated by the Federal government in 202193 now intends for the daily increase in the conversion to residential and transport terrain to be reduced to less than 30 ha per day by 2030. The Integrated Environment Programme⁹⁴ launched by BMUB in 2016, goes beyond this objective by setting 20 ha per day as an interim target for 2030, from the perspective that by 2050 the transition to circular land use will be completed, thus reducing the conversion of land use to net zero. However, to fulfil this objective will require substantially greater endeavours.

The Federal / Länder Working Group Soil Protection (LABO) coordinates the Länder’s concerns in respect of soil protection while also dealing with issues regarding climate change and its impacts on soil. With several position papers, LABO has taken a stand on important challenges, such as in 2017 with the position paper entitled ‘Significance and protection of peat soils’⁹⁵ and in 2021 – jointly with LAWA – with the position paper ‘Degradation of soils – soil erosion by water’⁹⁶.

^{94 - BMUB – Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit (Hg.) 2016: Den ökologischen Wandel gestalten – Integriertes Umweltprogramm 2030. Berlin, 127 pp. https://www.bmuv.de/publikation/den-oekologischen-wandel-gestalten.}

^{95 - LABO – Bund/Länder-Arbeitsgemeinschaft Bodenschutz 2017: Bedeutung und Schutz von Moorböden. Positionspapier. Kiel, 3 pp. https://www.labo-deutschland.de/documents/171222_LABO_Positionspapier_Moorbodenschutz.pdf.}

^{96 - LAWA – Bund/Länder-Arbeitsgemeinschaft Wasser, LABO 2021: Degradation von Böden – Bodenerosion durch Wasser. Positionspapier. München, 11 pp. https://www.lawa.de/documents/lawa-labo-positionspapier-degradation-von-boede-bodenerosion-durch-wasser-barrierefrei_1689855168.pdf.}