Climate Impacts: Field of Action Soils

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

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.

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 water in agriculturally used soils and in forest soils – case study

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.