soil erosion is a natural process, occurring over geological time, and indeed it is a process that is essential for soil formation in the first place. With respect to soil degradation, most concerns about erosion are related to accelerated erosion, where the natural rate has been significantly increased mostly by human activity. Soil erosion by water is a widespread problem throughout Europe.
The processes of soil erosion involve detachment of material by two processes, raindrop impact and flow traction; and transported either by saltation through the air or by overland water flow. Runoff is the most important direct driver of severe soil erosion by water and therefore processes that influence runoff play an important role in any analysis of soil erosion intensity.
By removing the most fertile topsoil, erosion reduces soil productivity and, where soils are shallow, may lead to an irreversible loss of natural farmland. Even where soil depth is good, loss of the topsoil is often not conspicuous but nevertheless potentially very damaging. Severe erosion is commonly associated with the development of temporary or permanently eroded channels or gullies that can fragment farmland. The soil removed by runoff from the land, for example during a large storm, accumulates below the eroded areas, in severe cases blocking roadways or drainage channels and inundating buildings.
... removed by the action of water or wind: such ‘background’ (or ‘geological’) soil erosion has been occurring for some ... the first soil. In general, background erosion removes soil at roughly the same rate as soil is formed. But ‘accelerated’ soil erosion – loss ...
Erosion rate is very sensitive to both climate and land use, as well as to detailed conservation practice at farm level. The Mediterranean region is particularly prone to erosion because it is subject to long dry periods followed by heavy bursts of erosive rain, falling on steep slopes with fragile soils. This contrasts with NW Europe where soil erosion is less because rain falling on mainly gentle slopes is evenly distributed throughout the year and consequently, the area affected by erosion is less extensive than in southern Europe. However, erosion is still a serious problem in NW and central Europe, and is on the increase. In parts of the Mediterranean region, erosion has reached a stage of irreversibility and in some places erosion has practically ceased because there is no more soil left.
With a very slow rate of soil formation, any soil loss of more than 1 t ha-1yr-1 can be considered as irreversible within a time span of 50-100 years. Losses of 20 to 40 t ha-1 in individual storms, that may happen once every two or three years, are measured regularly in Europe with losses of more than 100 t ha-1in extreme events. The main causes of soil erosion are still inappropriate agricultural practices, deforestation, overgrazing, forest fires and construction activities.
In a period of rapid changes in both climate and land use, due to global change, revised agricultural policies and changing international market forces, it is vitally important to be able to assess the state of soil erosion at a European level, using an objective methodology. This methodology must also allow the assessment of erosion to be repeated as conditions change, or to explore the broad scale implications of prospective global or European-wide changes in land utilization. The results of applying such a methodology can provide estimates of the overall costs attributable to erosion under present and changed conditions, and objectively identify areas where more detailed study is needed and possible remedial action.