When strong winds hit bare or only poorly covered soil, soil material is stirred up and transported, sometimes over long distances, through the open landscape. The result is the stealthy loss of fertile soil. Neighboring sites and ecosystems can be affected. Also, for people dangerous situations are possible, for example due to impaired visibility.
If a soil is not protected by a closed vegetation cover - for example on arable land - strong winds can create turbulence at the earth's surface, soil particles can move and being transported. The long-term consequence is the loss of soil, accompanied by a reduction in soil fertility and thus a decrease in the yield capacity of agricultural soils.
Wind speeds of between 6 and 8 m per second (moderate to fresh wind; measured at a height of 10 meters above ground level) are already considered to trigger erosive soil loss by wind (BMEL 2001). Depending on the wind speed and the size of soil particles, they move in form of:
Suspension (floating), which concerns smaller particles < 0.1 millimeter,
Saltation (jumping), which concerns particles between 0.1 and 0.5 millimeters, or
Reptation (rolling/creeping) for larger particles > 0.5 millimeters.
Jumping and rolling soil particles are often again deposited in short distances at wind barriers. In contrast, the fine, usually most fertile soil components (silt, clay minerals, humus and plant nutrients), can floatingly be transported over long distances. They get lost from the soil surface, while the coarser and humus-poor soil particles remain. This leads to a degradation of the soil structure and soil functions such as water and nutrient storage capacity decrease. This results in a reduction of soil fertility accompanied by a loss of biodiversity.
At the deposition sites, damage can be caused, for example, by plant cover and leaf abrasion (see figure). Nutrients and pollutants can increasingly adsorb to the fine particles, which can contribute to pollutant enrichment or eutrophication in neighboring sensitive terrestrial ecosystems or water bodies (see for example Critical Loads).
However, soil loss by wind erosion can also be dangerous to humans, for example when dust clouds form that lead to massive visibility obstructions (Wurbs and Steininger 2017).
What facilitates soil loss by wind erosion?
The extent of soil loss by wind depends regionally or locally on natural, site-specific factors, like:
Erodibility of soils: The susceptibility of soils to soil loss is conditioned by their genesis and structure such as soil type and topsoil humus content.
Climate conditions: The amount of precipitation and its seasonal distribution directly affects soil moisture. Drought favors soil loss by wind. In addition, the wind speeds on the regional scale are highly important. They determine the erosive effectiveness of the wind.
In addition, there are a number of other factors which may influence each other, like:
Management/soil cover: The type of management, such as duration and timing of missing soil cover by plants and plant residues, has a major influence. Uncovered or poorly covered soils provide a favorable target for winds and their erosive effects. A soil coverage of 30 percent already starts counteracting soil loss by wind erosion. Whereas a closed soil cover almost prevents the possibility of wind attack. The degree of soil cover depends both on the cultivated crop types (growth cycles) themselves and on applied conservation management practices such as intercropping, mulching and the degree of tillage.
Landscape and structure of agricultural land: Wind-open agricultural land and landscapes where sufficient wind barriers are missing also favors the erosive effect of the wind. According to the German Thünen Institute, a susceptibility to soil loss by wind erosion can be assumed as a rough orientation value at less than five kilometers of corridor elements per square kilometer.
Climate changes: An increase of dry periods, which cause decreasing soil moisture, and an increase in mean wind speeds favor soil loss by wind.
Where are the hotspots of soil loss risk by wind erosion in Germany?
To assess the soil loss risk due to wind erosion on the regional scale it is necessary to use models. For German the approches according to DIN 19706:2013-02 were used. A detailed description of the data basis used, the approaches applied and a discussion of the results can be found in the following UBA report "Bundesweite Gefährdung der Böden durch Winderosion..." (Wurbs and Steininger 2017).
The results show that in Germany, based on the content of soils and considering mean wind speeds, the natural soil loss risk due to wind erosion is highest in the north, on the medium and light lowland sites used for agriculture. High and very high risk levels are found in larger parts of the northern German “Länder” Schleswig-Holstein, Mecklenburg-Vorpommern, and western Lower Saxony (Figure 1). Arable land in the Northern German lowlands of Brandenburg, Saxony-Anhalt and North Rhine-Westphalia show medium risk levels.
In a further step, the natural soil loss risk due to wind erosion can be linked with the protection levels of wind barriers such as tree rows and hedges to identify the potential soil loss risk due to wind erosion (Figure 2). Basic information are the main wind directions to estimate windward and leeward effects and mean heights of wind barriers. Areas with high to very high potential soil loss risk are mainly found in the German “Länder” Schleswig-Holstein and in western Lower Saxony.
Since the cultivation of arable land plays an important role, in particular via the land cover factor, the cultivation-related soil loss risk due to wind erosion was also identified. The basis was the regionally cultivated crop type shares on the arable land. For the year 2010, it can be shown that a medium to very good management-related protection effect is achieved on around 68 percent of the cultivated area. However, only low to very low protection effects are found on around 32 percent of the cultivated areas. In some cases, cultivation systems with a high risk were concentrated on sites with a high natural risk for soil loss by wind erosion.
The principles and recommendations for "good agricultural practice” (GAP) in soil protection according to §17, section 2, number 4 and 5 of the German Federal Soil Protection Act (BBodSchG) are decisive for soil loss protection in agricultural use:
Soil loss is avoided applying site-appropriate management practices, especially by considering slope, water and wind conditions, and soil cover,
structural elements, especially hedges, field copses, field margins and field terraces are necessary for soil protection and should be preserved.
Both more diversity in management practices (e.g. diverse crop rotations, cultivation of catch crops, undersowing) and a higher structural diversity in the agricultural landscape itself (establishment of buffer strips, windbreak plantings or agroforestry systems) as well as land-use changes and the establishment of biotopes such as flower strips contribute to efficient soil loss control.
Especially in view of the predicted climate changes, increasing efforts in the implementation of precautionary measures to protect against erosive soil loss are required. Model observations in selected test areas show that climate-related influences such as increasing drought and increasing mean wind speeds are expected to increase the natural soil loss risk due to wind. This can only be countered with structural adjustments in the landscape and adjustments in the type of management and cropping systems.
The UBA’s motto, For our environment (“Für Mensch und Umwelt”), sums up our mission pretty well, we feel. In this video we give an insight into our work.
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