Impacts of Climate Change
Table of Contents
Soil erosion by water
Water erosion involves the displacement of soil material at the soil surface by water. The topsoil removed in this way is either deposited elsewhere or flushed into a body of water. Erosion risk is influenced by the amount and intensity of precipitation, the slope, the soil type, the soil structure (including humus content), the degree of soil cover, and the land use and cultivation. If the amount of precipitation exceeds the infiltration capacity of the soil, the water runs off the surface and thus increases the risk of soil erosion. This applies in particular to soils that are compacted and temporarily without plant cover. Sloping areas with sand-rich soils are particularly at risk of water erosion.
Soil erosion through water erosion results in a reduction of soil thickness, loss of nutrient-rich and humus-rich topsoil and thus loss of soil fertility. If it enters water bodies, this can lead to water eutrophication through increased growth of algae and cyanobacteria. Consequential damage from soil removal and material deposition would continue to be the impairment of agricultural use through silting, the silting of water bodies or receiving water bodies, the impacts of traffic and settlement areas and sewer systems, and the decline of biological diversity.
Climate change may lead to a shift in precipitation patterns, i.e. periods of high temperatures and low precipitation in the spring and summer months and an increase in precipitation in the winter months. More frequent and longer dry periods in the summer half-year lead to an increase in the drying out of the topsoil. Since a severely dried-out soil initially has poor water absorption capacity when precipitation begins, surface runoff occurs, taking soil particles with it. Climate change could increase the probability of soil erosion events due to an increase in heavy rainfall events, especially in winter.
Indicator from the monitoring on the DAS: Rainfall erosivity – case study
Soil erosion by wind
Wind erosion is the erosion of soil by wind. Wind erosion is significantly influenced by the factors topography, soil moisture, type of land use, soil cover and wind openness, type of cultivation on agricultural land and its intensity. Areas that are open to the wind, dry and very flat are particularly at risk.
Through land use humans influence wind erosion hazards. Soil cultivation and the degree of soil cover by plants or plant residues are of importance. Grassland areas are not affected by wind erosion due to the year-round closed vegetation cover. Sandy soils in particular are highly susceptible to wind erosion, less soils with high humus content. Soil type and humus content also affect the water retention capacity of the site. The drier the topsoil, the greater the erosion risk of the site under consideration. Visible damage caused by wind erosion usually occurs seasonally and rather sporadically, so that soil erosion is less noticeable than in the case of water erosion due to its large scale. In addition, wind occurs with a high variability, i.e. wind directions vary, which means that the affected areas can also differ.
Wind erosion causes the loss of fine soil and humus in particular. This damages the soil structure and has a negative effect on the water storage capacity of the topsoil. The removal of the smallest soil particles is relevant because components relevant to soil fertility, such as clay minerals, humus and plant nutrients bound to them, are lost with it. In agriculture, this can lead to economic damage and, in the long term, to a decline in site productivity. At the places where the transported soil material is deposited, nutrients and possibly also pollutants may enter sensitive ecosystems (e.g. waters), and there may be hazards due to reduced visibility in traffic and damage to buildings, technical facilities and infrastructure.
Increasing dry periods in the spring and summer months due to climate change, as well as the potential increase in high wind events, could make soils even more susceptible to wind erosion in the future.
Water shortage in the soil
Soil plays a significant role as a water reservoir. Precipitation water falling on the soil infiltrates in and is retained in the soil pores. Both water uptake by plants and water evaporation from the soil surface reduce the amount of water stored in the soil. Lack of rainfall ensures that the water reservoir is not replenished and the amount of water available for plants becomes increasingly scarce. As a result, plants experience drought stress and growth is reduced unless they can access water from deeper soil layers through their plant roots. If the phase without precipitation lasts longer, the plants begin to die.
A lack of water in the soil has far-reaching consequences, especially for agriculture. In the course of drought stress, there are yield losses as well as a lower quality of the harvested products and thus economic damage. The same applies to forestry and silviculture. A lack of water is particularly serious in soils that are permanently under water (e.g. bogs, river floodplains). Here, as a further impact, rare plant and animal species may be endangered.
Prolonged drought conditions with lack of precipitation and reduced infiltration rate continues to have an impact on groundwater foundation. There is a change in the depth of the groundwater surface. In very dry summers, the self-supply of drinking water can be reduced in particularly affected regions and, in extreme cases, can come to a standstill because domestic wells go dry. In dry periods, low groundwater levels are particularly problematic for shallow-rooted trees and groundwater-dependent biotopes. For rivers and lakes that are fed underground by groundwater, falling groundwater levels reduce underground runoff into surface waters. This can possibly lead to a reversal of the flow direction.
An adverse change in the soil water balance due to climate change as a result of higher temperatures, lower precipitation in summer and prolonged dry phases could lead to significant reductions in yields in agriculture and forestry in the future and have an even greater impact on groundwater formation.
Indicator from the monitoring on the DAS: Soil moisture levels in farmland soil
Other climate impacts
Waterlogging: In the event of prolonged and heavy precipitation that cannot percolate, the soil may become waterlogged, which impair the aeration of the soil and thus the oxygen supply of the plant roots. In addition, waterlogging restricts the accessibility of soils. Due to climate change, a slight increase in rainfall events in autumn is to be expected. In spring and summer, on the other hand, there may be less waterlogging.
Leachate water: The portion of precipitation that is not stored in the soil flows as leachate water into deeper soil layers and contributes to groundwater foundation there. An increase in summer drought will in future lead to lower leachate rates in the summer months and increasingly shift groundwater foundation to late autumn and winter. As this takes place outside the period with plant cover, unused nutrients can enter the aquifer with the backup water and thus pollute the groundwater.
Adaptation to Climate Change
Measures against water erosion
Arable and crop measures against water erosion are aimed at maintaining and building up a stable soil structure, preventing or at least severely restricting the mobilisation of soil particles during heavy rainfall and surface silting. This includes minimising the periods without soil cover through the cultivation of catch crops, subseeds and the leaving or application of a soil-protecting mulch layer (e.g. straw, crop residues, manure, green cuttings, and compost). A soil cover not only protects the soil from the direct impact of raindrops, but also maintains or builds up stable soil aggregates that reduce siltation through the activity of soil organisms. An area-wide mulch layer has a particularly erosion-reducing effect, as it also slows down runoff.
The stability of the soil can be improved by reducing the tillage depth and intensity. In this way, permanent no-till conservation tillage preserves the natural soil structure and reduces the risk of erosion. The use of heavy vehicles and machines can lead to soil compaction and thus limit the infiltration of rainwater into the soil. Soil cultivation methods can be adapted in such a way that the total mass and the specific surface pressure are better distributed and thus the load-bearing capacity of the soils is less stressed. This can be achieved by using wide tyres with low internal tyre pressure and a large contact area or by using lighter machines.
On sloping sites, the following adaptation options are available: cultivation across the slope, the creation of green strips, hedges and roadside ditches running across the slope to slow down runoff, the creation of small terraces, the creation of retention areas as sedimentation space in the slope area, professional water drainage from the upstream area, and the permanent planting of partial areas particularly at risk of erosion.
In addition to these technical measures, legal, political and management measures may contribute to the prevention of water erosion. Soil protection policy should focus on soil-related adaptation measures. Soil functions relevant to climate adaptation should be given greater consideration in laws and in planning and approval procedures. Spatial planning (e.g. regional planning, land consolidation procedures) could contribute to reducing water erosion risks by designating priority areas (e.g. green strips, hedge planting) for soil protection. In the settlement area, areas with no or only little vegetation can be converted into green spaces as compensation areas for construction projects. Concrete specifications regarding the reduction of land consumption and land unsealing in settlement and transport development may also require a political decision. Active protection against water erosion may consist of abandoning particularly endangered areas in favour of other, less erosion-sensitive uses (e.g. establishment of permanent grassland, forest or woodland areas).
Erosion assessment is an important management measure for planning concrete adaptation measures. It allows an assessment of potential erosion damage and the spatial impact of climate change. Also of importance is the establishment of a climate change-related soil monitoring system that bundles meaningful information on soils, land uses and regional climate changes in order to better assess climate impacts on soil functions. The 2nd Progress Report on the German Adaptation Strategy (DAS) states that a climate impact soil monitoring network should be established in order to provide users in administration and science with easy access to soil-related measurement data.
Indicator from the monitoring on the DAS: Permanent grassland
Measures against soil erosion by wind
The determination of the risk of wind erosion at a site represents an important planning basis for concrete measures against soil erosion by wind. These measures may be based on factors that influence wind erosion: Landscape structure, soil roughness, vegetation and land cover. In addition, land use changes are conceivable.
Linear landscape structures, such as hedges, hedgerows and stone walls, may act as flow obstacles in sparsely forested regions and thus protect the soil from wind erosion. It should be noted that, in addition to the one-off investment, long-term costs may arise for the maintenance and upkeep of such corridor elements. In addition, the creation of new corridors entails a certain loss of agricultural land. However, the positive effects outweigh this. In addition to erosion control, hedges contribute to an improved microclimate and soil water balance and are important for biodiversity and biotope connectivity.
Dense soil cover with vegetation, subseeds or mulch as well as a high roughness of the topsoil reduces the wind speed directly at the soil surface. A soil cover of > 25 % already provides effective wind erosion protection. The cultivation of alternating crops with different growth heights on smaller, neighbouring areas also leads to a reduction of wind speeds near the soil surface. The soil surface should be left as rough as possible after tillage.
In areas with a high risk of wind erosion, it is conceivable to convert arable land to extensive permanent grassland use or to take it out of use altogether and leave it to natural succession. The conversion of land use also includes the afforestation of formerly agricultural land, the creation of biotopes (e.g. establishment of permanent flowering strips in fields). Another objective can be land consolidation, which reduces the length of the field perpendicular to the main wind direction by re-cutting the agricultural land in order to minimise the area exposed to the wind. Such long-term land use changes are usually only possible with political support and the provision of financial resources.
Measures against water shortage in the soil
Targeted adaptation measures to a decreasing water content in the soil are of concern in agriculture, in the landscape, but also in settlement areas.
In agriculture, sufficient humus supply to the soil is of primary importance, as this improves the water retention capacity. The following measures, among others, are important for increasing the humus content: a site-appropriate, diverse crop rotation with a balanced relationship between humus-consuming (e.g. maize, sugar beet, potato) and humus-productive catch crops and subseeds (e.g. clover grass), a periodic use of grassland, a sufficient supply of organic matter to the soil through the crop residues (e.g. straw, roots) remaining on the field at harvest and through organic farm manure (e.g. farmyard manure, liquid manure, compost), as well as conservation/non-turning tillage. A permanent soil cover together with the crops protects the soil from drying out. Soil compaction should be avoided as far as possible, as a good soil structure is the prerequisite for oxygen and water supply and thus for optimal microbial activity. The practices mentioned here are implemented in particular within the framework of organic farming, which is why its promotion may also counteract the occurrence of water deficiency situations in soils.
In principle, irrigation is possible in agriculture if plant development is inhibited by soil water content in critical phases. If irrigation is used, it should be carried out according to need, efficiently and with as little evaporation loss as possible. Crops may also be adapted to low soil water contents and thus to drought stress by cultivating drought-tolerant plant cultures and varieties. This can minimise yield losses.
Where land use allows, reducing drainage, re-wetting and allowing flooding help to retain water more firmly in the landscape. This prepares for and could help to survive dry periods. If land can be made available for the re-wetting of peatlands, this will help the regional and water balance.
In the settlement area, the aim of urban planning should be to achieve an approximation to the natural water balance. To this end, with the help of nature-based adaptation measures, precipitation water is no longer exclusively drained into the urban sewage system, but is instead discharged into open and green spaces; it percolates and thus remains in the city. Nature-based elements, such as swale systems, strengthen decentralised rainwater infiltration and help to increase soil moisture and groundwater recharge in urban areas. In hot and dry periods, this can improve the water supply for plants and improve the urban climate through evaporative cooling of the soil and plants ("Sponge City principle"). An important measure in this context is the unsealing of surfaces. On the part of urban land use planning, the regulation of land use by settlement and infrastructure, the keeping of areas free for precipitation infiltration and the securing of green spaces contribute to the adaptation to water shortage risks. During dry periods, irrigation measures may be created, such as using service water to irrigate urban green spaces, attaching water bags to newly planted urban trees or organising watering partnerships in neighbourhoods. Such measures should in any case be efficient, water-saving and hygienically safe.
Indicator from the monitoring on the DAS: Humus content of arable land – case study