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{{Short description|Displacement of soil by water, wind, and lifeforms}}File:Eroding rill in field in eastern Germany.jpg|thumb|right|An actively eroding rill on an intensively-farmed field in eastern GermanyGermany(File:Soil erosion 05.jpg|thumb|Soil erosion)Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, and animals (including humans). In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolian) erosion, zoogenic erosion and anthropogenic erosion such as tillage erosion.JOURNAL, Apollo, M., Andreychouk, V., Bhattarai, S.S., Short-Term Impacts of Livestock Grazing on Vegetation & Track Formation in a High Mountain Environment, A Case Study from the Himalayan Miyar Valley (India), Sustainability, 10, 4, 2018-03-24, 2071-1050, 10.3390/su10040951, 951, free, Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing a serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks. Soil erosion could also cause sinkholes.Human activities have increased by 10–50 times the rate at which erosion is occurring world-wide.Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems worldwide.BOOK, Blanco, Humberto, Lal, Rattan, amp, Soil and water conservation, Principles of Soil Conservation & Management, Springer, 2010, 978-90-481-8529-0, 2,weblink JOURNAL, Pimentel, David, 2006-02-01, Soil Erosion: A Food and Environmental Threat,weblink Environment, Development and Sustainability, en, 8, 1, 119–137, 10.1007/s10668-005-1262-8, 6152411, 1573-2975, Intensive agriculture, deforestation, roads, acid rains, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion.BOOK, Julien, Pierre Y., Erosion and Sedimentation, Cambridge University. (Press, 2010, 978-0-521-53737-7, 1,weblink However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils.

Physical processes

Rainfall and surface runoff

File:Water and soil splashed by the impact of a single raindrop.jpg|thumb|right|Soil and water being splashed by the impact of a single raindropraindropRainfall, and the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. Splash erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by sheet erosion, then rill erosion and finally gully erosion (the most severe of the four).BOOK, Toy, Terrence J., Soil Erosion: Processes, Prediction, Measurement, & Control, John Wiley & Sons, 2002, 978-0-471-38369-7, 60–61,weblink etal, BOOK, Zachar, DuÅ¡an, Classification of soil erosion, Soil Erosion, 10, Elsevier, 1982, 978-0-444-99725-8, 48,weblink In splash erosion, the impact of a falling raindrop creates a small crater in the soil,See figure 4 in JOURNAL, Obreschkow, Confined Shocks inside Isolated Liquid Volumes – A New Path of Erosion?, 2011, 1109.3175, Physics of Fluids, 2011PhFl...23j1702O, 10.1063/1.3647583, 23, 10, 101702, 59437729, ejecting soil particles.JOURNAL, Cheraghi M., Jomaa S., Sander G. C., Barry D. A., 2016, Hysteretic sediment fluxes in rainfall-driven soil erosion: Particle size effects,weblink Water Resour. Res., 52, 11, 8613–8629, 10.1002/2016WR019314, 2016WRR....52.8613C, 13077807, The distance these soil particles travel can be as much as 0.6 m (two feet) vertically and 1.5 m (five feet) horizontally on level ground.If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs. If the runoff has sufficient flow energy, it will transport loosened soil particles (sediment) down the slope.BOOK, Food and Agriculture Organization, Types of erosion damage, Soil Erosion by Water: Some Measures for Its Control on Cultivated Lands, United Nations, 1965, 978-92-5-100474-6, 23–25,weblink Sheet erosion is the transport of loosened soil particles by overland flow.File:Rummu aherainemägi2.jpg|thumb|A spoil tip covered in rills and gullies due to erosion processes caused by rainfall: Rummu, EstoniaEstoniaRill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimeters (about an inch) or less and along-channel slopes may be quite steep. This means that rills exhibit hydraulic physics very different from water flowing through the deeper wider channels of streams and rivers.JOURNAL, Nearing, M.A., Norton, L.D., Bulgakov, D.A., Larionov, G.A., West, L.T., Dontsova, K.M., 1997, Hydraulics and erosion in eroding rills, Water Resources Research, 33, 4, 865–876, 10.1029/97wr00013, 1997WRR....33..865N, free, Gully erosion occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth.BOOK, Poesen, Jean, Gully erosion in Europe, Boardman, John, Poesen, Jean, Soil Erosion in Europe, John Wiley & Sons, 2007, 978-0-470-85911-7, 516–519,weblink etal, BOOK, Poesen, Jean, Gully erosion in dryland environments, Bull, Louise J., Kirby, M.J., Dryland Rivers: Hydrology and Geomorphology of Semi-Arid Channels, John Wiley & Sons, 2002, 978-0-471-49123-1,weblink etal, BOOK, Borah, Deva K., Watershed sediment yield, Garcia, Marcelo H., Sedimentation Engineering: Processes, Measurements, Modeling, and Practice, ASCE Publishing, 2008, 978-0-7844-0814-8, 828,weblink etal, Another cause of gully erosion is grazing, which often results in ground compaction. Because the soil is exposed, it loses the ability to absorb excess water, and erosion can develop in susceptible areas.WEB,weblink Gully erosion - Agriculture, 4 June 2020,

Rivers and streams{{Anchor|gully erosion|ephemeral gully erosion}}

{{further|topic=water's erosive ability|Hydraulic action}}File:Dobbingstone Burn - geograph.org.uk - 1291882.jpg|thumb|Dobbingstone Burn, Scotland—This photo illustrates two different types of erosion affecting the same place. Valley erosion is occurring due to the flow of the stream, and the boulders and stones (and much of the soil) that are lying on the edges are glacial tillglacial tillValley or stream erosion occurs with continued water flow along a linear feature. The erosion is both downward, deepening the valley, and headward, extending the valley into the hillside, creating head cuts and steep banks. In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is relatively steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain. The stream gradient becomes nearly flat, and lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood, when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone that erodes: suspended abrasive particles, pebbles and boulders can also act erosively as they traverse a surface, in a process known as traction.Ritter, Michael E. (2006) "Geologic Work of Streams" {{webarchive|url=https://web.archive.org/web/20120506040721weblink |date=2012-05-06 }} The Physical Environment: an Introduction to Physical Geography University of Wisconsin, {{OCLC|79006225}}Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from changes on the bed of the watercourse, which is referred to as scour. Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times.BOOK,weblink Stream hydrology: an introduction for ecologists, Nancy D. Gordon, Erosion and Scour, 978-0-470-84357-4, 2004-06-01, John Wiley and Sons, Thermal erosion is the result of melting and weakening permafrost due to moving water.WEB,weblink Thermal Erosion, NSIDC Glossary, National Snow and Ice Data Center, 21 December 2009,weblink" title="web.archive.org/web/20101218124656weblink">weblink 2010-12-18, live, It can occur both along rivers and at the coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials.JOURNAL, 10.1002/esp.592, Fluvial thermal erosion investigations along a rapidly eroding river bank: application to the Lena River (central Siberia), 2003, Costard, F., Dupeyrat, L., Gautier, E., Carey-Gailhardis, E., Earth Surface Processes and Landforms, 28, 1349–1359, 2003ESPL...28.1349C, 12, 131318239, Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the Arctic coast, where wave action and near-shore temperatures combine to undercut permafrost bluffs along the shoreline and cause them to fail. Annual erosion rates along a {{convert|100|km|mi|abbr=off|adj=on}} segment of the Beaufort Sea shoreline averaged {{convert|5.6|m|ft|abbr=off}} per year from 1955 to 2002.JOURNAL, Jones, B.M., Hinkel, K.M., Arp, C.D., Eisner, W.R., 2008, Modern Erosion Rates and Loss of Coastal Features and Sites, Beaufort Sea Coastline, Alaska, Arctic, 61, 4, 361–372,weblink 10.14430/arctic44, dead,weblink" title="web.archive.org/web/20130517101602weblink">weblink 2013-05-17, 10535/5534, free,

Floods

At extremely high flows, kolks, or vortices are formed by large volumes of rapidly rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called rock-cut basins. Examples can be seen in the flood regions result from glacial Lake Missoula, which created the channeled scablands in the Columbia Basin region of eastern Washington.See, for example: BOOK, Alt, David, Glacial Lake Missoula & its Humongous Floods

year=2001

url=https://books.google.com/books?id=s4y3c8fxeEwC, Wind erosion File:Im Salar de Uyuni.jpg|thumb|Árbol de Piedra, a rock formation in the Altiplano, BoliviaBoliviaWind erosion is a major geomorphological force, especially in arid and semi-arid regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage—especially after being increased far above natural rates by human activities such as deforestation, urbanization, and agriculture.BOOK, Zheng, Xiaojing, Huang, Ning, amp, Mechanics of Wind-Blown Sand Movements, Springer, 2009, 978-3-540-88253-4, 7–8,weblink BOOK, Cornelis, Wim S., Hydroclimatology of wind erosion in arid and semi-arid environments, D'Odorico, Paolo, Porporato, Amilcare, Dryland Ecohydrology, Springer, 2006, 978-1-4020-4261-4, 141,weblink Wind erosion is of two primary varieties: deflation, where the wind picks up and carries away loose particles; and abrasion, where surfaces are worn down as they are struck by airborne particles carried by wind. Deflation is divided into three categories: (1) surface creep, where larger, heavier particles slide or roll along the ground; (2) saltation, where particles are lifted a short height into the air, and bounce and saltate across the surface of the soil; and (3) suspension, where very small and light particles are lifted into the air by the wind, and are often carried for long distances. Saltation is responsible for the majority (50–70%) of wind erosion, followed by suspension (30–40%), and then surface creep (5–25%).BOOK, Blanco, Humberto, Lal, Rattan, amp, Wind erosion, Principles of Soil Conservation and Management, Springer, 2010, 978-90-481-8529-0, 56–57,weblink BOOK, Balba, A. Monem, Desertification: Wind erosion, Management of Problem Soils in Arid Ecosystems, CRC Press, 1995, 978-0-87371-811-0, 214,weblink Silty soils tend to be the most affected by wind erosion; silt particles are relatively easily detached and carried away.Jefferson, I.F., Smalley>I.J. 1999. Saltating sand erodes metastable loess ground: events in the impact zone.weblink {{Webarchive|url=https://web.archive.org/web/20170211122659weblink |date=2017-02-11 }}Wind erosion is much more severe in arid areas and during times of drought. For example, in the Great Plains, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.BOOK, Wiggs, Giles F.S., Geomorphological hazards in drylands, Thomas, David S.G., Arid Zone Geomorphology: Process, Form and Change in Drylands, John Wiley & Sons, 2011, 978-0-470-71076-0, 588,weblink Mass movement (File:NegevWadi2009.JPG|thumb|Wadi in Makhtesh Ramon, Israel, showing gravity collapse erosion on its banks)Mass movement is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of gravity.BOOK, Van Beek, Rens, Hillside processes: mass wasting, slope stability, and erosion, Norris, Joanne E., etal, Slope Stability and Erosion Control: Ecotechnological Solutions, Springer, 2008, 978-1-4020-6675-7,weblink BOOK, Gray, Donald H., Sotir, Robbin B., amp, Surficial erosion and mass movement, Biotechnical and Soil Bioengineering Slope Stabilization: A Practical Guide for Erosion Control, John Wiley & Sons, 1996, 978-0-471-04978-4, 20,weblink Mass movement is an important part of the erosional process, and is often the first stage in the breakdown and transport of weathered materials in mountainous areas.BOOK, Nichols, Gary, Sedimentology and Stratigraphy, John Wiley & Sons, 2009, 978-1-4051-9379-5, 93,weblink It moves material from higher elevations to lower elevations where other eroding agents such as streams and glaciers can then pick up the material and move it to even lower elevations. Mass-movement processes are always occurring continuously on all slopes; some mass-movement processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a landslide. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a scree slope.JOURNAL, Sun, Wenyi, Shao, Quanqin, Liu, Jiyuan, Zhai, Jun, 2014-10-01, Assessing the effects of land use and topography on soil erosion on the Loess Plateau in China,weblink CATENA, en, 121, 151–163, 10.1016/j.catena.2014.05.009, 2014Caten.121..151S, 0341-8162, Slumping happens on steep hillsides, occurring along distinct fracture zones, often within materials like clay that, once released, may move quite rapidly downhill. They will often show a spoon-shaped isostatic depression, in which the material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along highways where it is a regular occurrence.JOURNAL, van den Berg, J., van de Wal, R. S. W., Milne, G. A., Oerlemans, J., 2008-05-31, Effect of isostasy on dynamical ice sheet modeling: A case study for Eurasia, Journal of Geophysical Research, en, 113, B5, B05412, 10.1029/2007JB004994, 2008JGRB..113.5412V, 0148-0227, free, Surface creep is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe the rolling of dislodged soil particles {{convert|0.5|to|1.0|mm|abbr=on|2}} in diameter by wind along the soil surface.BOOK, Soils and Their Environment, Hassett, John, Prentice Hall, 1992, 9780134840499, 377,weblink Tillage erosion {{excerpt|Tillage erosion}} Factors affecting soil erosion Climate The amount and intensity of precipitation is the main climatic factor governing soil erosion by water. The relationship is particularly strong if heavy rainfall occurs at times when, or in locations where, the soil's surface is not well protected by vegetation. This might be during periods when agricultural activities leave the soil bare, or in semi-arid regions where vegetation is naturally sparse. Wind erosion requires strong winds, particularly during times of drought when vegetation is sparse and soil is dry (and so is more erodible). Other climatic factors such as average temperature and temperature range may also affect erosion, via their effects on vegetation and soil properties. In general, given similar vegetation and ecosystems, areas with more precipitation (especially high-intensity rainfall), more wind, or more storms are expected to have more erosion.In some areas of the world (e.g. the mid-western US and the Amazon Rainforest), rainfall intensity is the primary determinant of erosivity, with higher intensity rainfall generally resulting in more soil erosion by water. The size and velocity of rain drops is also an important factor. Larger and higher-velocity rain drops have greater kinetic energy, and thus their impact will displace soil particles by larger distances than smaller, slower-moving rain drops.BOOK, Blanco, Humberto, Lal, Rattan, amp, Water erosion, Principles of Soil Conservation and Management, Springer, 2010, 978-90-481-8529-0, 29–31,weblink In other regions of the world (e.g. western Europe), runoff and erosion result from relatively low intensities of stratiform rainfall falling onto previously saturated soil. In such situations, rainfall amount rather than intensity is the main factor determining the severity of soil erosion by water.Boardman, John & Poesen, Jean. Soil Erosion in Europe. John Wiley & Sons. {{ISBN|978-0-470-85911-7}} Soil structure and composition File:Dead Sea Coastal Erosion March 2012.JPG|thumb|Erosional gully in unconsolidated Dead Sea (Israel) sediments along the southwestern shore. This gully was excavated by floods from the Judean MountainsJudean MountainsThe composition, moisture, and compaction of soil are all major factors in determining the erosivity of rainfall. Sediments containing more clay tend to be more resistant to erosion than those with sand or silt, because the clay helps bind soil particles together.BOOK, Mirsal, Ibrahim A., Soil degradation, Soil Pollution: Origin, Monitoring & Remediation, Springer, 2008, 978-3-540-70775-2, 100,weblink Soil containing high levels of organic materials are often more resistant to erosion, because the organic materials coagulate soil colloids and create a stronger, more stable soil structure. The amount of water present in the soil before the precipitation also plays an important role, because it sets limits on the amount of water that can be absorbed by the soil (and hence prevented from flowing on the surface as erosive runoff). Wet, saturated soils will not be able to absorb as much rainwater, leading to higher levels of surface runoff and thus higher erosivity for a given volume of rainfall.BOOK, Torri, D., Slope, aspect and surface storage, Agassi, Menachem, Soil Erosion, Conservation, and Rehabilitation, CRC Press, 1996, 978-0-8247-8984-8, 95,weblink Soil compaction also affects the permeability of the soil to water, and hence the amount of water that flows away as runoff. More compacted soils will have a larger amount of surface runoff than less compacted soils.BOOK, Blanco, Humberto, Lal, Rattan, amp, Water erosion, Principles of Soil Conservation and Management, Springer, 2010, 978-90-481-8529-0, 29,weblink Vegetative cover {{See also|Vegetation and slope stability}}Vegetation acts as an interface between the atmosphere and the soil. It increases the permeability of the soil to rainwater, thus decreasing runoff. It shelters the soil from winds, which results in decreased wind erosion, as well as advantageous changes in microclimate. The roots of the plants bind the soil together, and interweave with other roots, forming a more solid mass that is less susceptible to both water and wind erosion. The removal of vegetation increases the rate of surface erosion.BOOK, Styczen, M.E., Morgan, R.P.C., amp, Engineering properties of vegetation, Morgan, R.P.C., Rickson, R. Jane, Slope Stabilization and Erosion Control: A Bioengineering Approach, Taylor & Francis, 1995, 978-0-419-15630-7,weblink Topography The topography of the land determines the velocity at which surface runoff will flow, which in turn determines the erosivity of the runoff. Longer, steeper slopes (especially those without adequate vegetative cover) are more susceptible to very high rates of erosion during heavy rains than shorter, less steep slopes. Steeper terrain is also more prone to mudslides, landslides, and other forms of gravitational erosion processes.BOOK, Whisenant, Steve G., Terrestrial systems, Perrow Michael R., Davy, Anthony J., Handbook of Ecological Restoration: Principles of Restoration, Cambridge University Press, 2008, 978-0-521-04983-2, 89,weblink BOOK, Blanco, Humberto, Lal, Rattan, amp, Water erosion, Principles of Soil Conservation and Management, Springer, 2010, 978-90-481-8529-0, 28–30,weblink BOOK, Wainwright, John, Brazier, Richard E., amp, Slope systems, Thomas, David S.G., Arid Zone Geomorphology: Process, Form and Change in Drylands, John Wiley & Sons, 2011, 978-0-470-71076-0,weblink Human activities that aid soil erosion Agricultural practices {{see also|agricultural pollution|overgrazing}}(File:Soil erosion at Hill Farm - geograph.org.uk - 1287527.jpg|thumb|Tilled farmland such as this is very susceptible to erosion from rainfall, due to the destruction of vegetative cover and the loosening of the soil during plowing.)Unsustainable agricultural practices increase rates of erosion by one to two orders of magnitude over the natural rate and far exceed replacement by soil production.JOURNAL, Montgomery, D. R., Soil erosion and agricultural sustainability, Proceedings of the National Academy of Sciences, 8 August 2007, 104, 33, 13268–13272, 10.1073/pnas.0611508104, 17686990, 1948917, 2007PNAS..10413268M, free, JOURNAL, Wuepper, David, Borrelli, Pasquale, Finger, Robert, January 2020, Countries and the global rate of soil erosion,weblink Nature Sustainability, en, 3, 1, 51–55, 10.1038/s41893-019-0438-4, 208539010, 2398-9629, The tillage of agricultural lands, which breaks up soil into finer particles, is one of the primary factors. The problem has been exacerbated in modern times, due to mechanized agricultural equipment that allows for deep plowing, which severely increases the amount of soil that is available for transport by water erosion. Others include monocropping, farming on steep slopes, pesticide and chemical fertilizer usage (which kill organisms that bind soil together), row-cropping, and the use of surface irrigation.BOOK, Blanco, Humberto, Lal, Rattan, amp, Tillage erosion, Principles of Soil Conservation and Management, Springer, 2010, 978-90-481-8529-0,weblink BOOK, Lobb, D.A., Soil movement by tillage and other agricultural activities, Jorgenson, Sven E., Applications in Ecological Engineering, Academic Press, 2009, 978-0-444-53448-4,weblink A complex overall situation with respect to defining nutrient losses from soils, could arise as a result of the size selective nature of soil erosion events. Loss of total phosphorus, for instance, in the finer eroded fraction is greater relative to the whole soil.JOURNAL, Bioavailable phosphorus in fine-sized sediments transported from agricultural fields, Poirier, S.-C., Whalen, J.K., Michaud, A.R., 2012, 76, 1, 258–267, 10.2136/sssaj2010.0441

bibcode=2012SSASJ..76..258P, Extrapolating this evidence to predict subsequent behaviour within receiving aquatic systems, the reason is that this more easily transported material may support a lower solution P concentration compared to coarser sized fractions.PHOSPHORUS LOSS IN OVERFERTILIZED SOILS: THE SELECTIVE P PARTITIONING AND REDISTRIBUTION BETWEEN PARTICLE SIZE SEPARATES >AUTHOR= SCALENGHE, R.

AUTHOR3= BARBERIS, E.

YEAR= 2007

ISSUE=11

DOI= 10.1016/J.EJA.2007.02.002

TITLE=ECOLOGY OF DESERT SYSTEMS

YEAR=2002

PAGE=65

grazing reduces vegetative cover and causes severe soil compaction, both of which increase erosion rates.IMESON, ANTON

TITLE=DESERTIFICATION, LAND DEGRADATION AND SUSTAINABILITY

YEAR=2012

PAGE=165,weblink Deforestation File:BURNED CLEAR-CUT AREA OF OLYMPIC NATIONAL TIMBERLAND WASHINGTON. NEAR OLYMPIC NATIONAL PARK - NARA - 555088.tif|thumb|In this clearcut, almost all of the vegetation has been stripped from the surface of steep slopes, in an area with very heavy rains. Severe erosion occurs in cases such as this, causing stream sedimentation and the loss of nutrient-rich topsoiltopsoilIn an undisturbed forest, the mineral soil is protected by a layer of leaf litter and an humus that cover the forest floor. These two layers form a protective mat over the soil that absorbs the impact of rain drops. They are porous and highly permeable to rainfall, and allow rainwater to slow percolate into the soil below, instead of flowing over the surface as runoff.BOOK, Sands, Roger, The environmental value of forests, Forestry in a Global Context, CABI, 2005, 978-0-85199-089-7, 74–75,weblink The roots of the trees and plantsThe mycelia of forest fungi also play a major role in binding soil particles together. hold together soil particles, preventing them from being washed away. The vegetative cover acts to reduce the velocity of the raindrops that strike the foliage and stems before hitting the ground, reducing their kinetic energy. However it is the forest floor, more than the canopy, that prevents surface erosion. The terminal velocity of rain drops is reached in about {{convert|8|m|ft|abbr=off}}. Because forest canopies are usually higher than this, rain drops can often regain terminal velocity even after striking the canopy. However, the intact forest floor, with its layers of leaf litter and organic matter, is still able to absorb the impact of the rainfall.BOOK, Goudie, Andrew, The human impact on the soil, The Human Impact on the Natural Environment, MIT Press, 2000, 978-0-262-57138-8, 188,weblinkweblink JOURNAL, Stuart, Gordon W., Edwards, Pamela J., amp, Concepts about forests and water, Northern Journal of Applied Forestry, 23, 1, 11–19, 2006,weblink 10.1093/njaf/23.1.11, free, 2015-10-05, 2017-07-01,weblink dead, Deforestation causes increased erosion rates due to exposure of mineral soil by removing the humus and litter layers from the soil surface, removing the vegetative cover that binds soil together, and causing heavy soil compaction from logging equipment. Once trees have been removed by fire or logging, infiltration rates become high and erosion low to the degree the forest floor remains intact. Severe fires can lead to significant further erosion if followed by heavy rainfall.BOOK, Goudie, Andrew, The human impact on the soil, The Human Impact on the Natural Environment, MIT Press, 2000, 978-0-262-57138-8, 196–197,weblinkweblink Globally one of the largest contributors to erosive soil loss in the year 2006 is the slash and burn treatment of tropical forests. In a number of regions of the earth, entire sectors of a country have been rendered unproductive. For example, on the Madagascar high central plateau, comprising approximately ten percent of that country's land area, virtually the entire landscape is sterile of vegetation, with gully erosive furrows typically in excess of {{convert|50|m|ft}} deep and {{convert|1|km|mi|abbr=off|1}} wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. This degrades the soil and causes the soil to become less and less fertile.THESIS, Shifting cultivation in the upland secondary forests of the Philippines: biodiversity and carbon stock assessment, and ecosystem services trade-offs in land-use decisions, University of Queensland Library, Sharif Ahmed, Mukul, 2016, 10.14264/uql.2016.222, Roads and human impact (File:Erosion pollution.jpg|thumb|Erosion polluted the Kasoa highway after downpour in Ghana)Human Impact has major effects on erosion processes—first by denuding the land of vegetative cover, altering drainage patterns, and compacting the soil during construction; and next by covering the land in an impermeable layer of asphalt or concrete that increases the amount of surface runoff and increases surface wind speeds.BOOK, Nîr, Dov, Man, a Geomorphological Agent: An Introduction to Anthropic Geomorphology, Springer, 1983, 978-90-277-1401-5, 121–122,weblink Much of the sediment carried in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals.BOOK, Randhir, Timothy O., Watershed Management: Issues and Approaches, IWA Publishing, 2007, 978-1-84339-109-8, 56,weblink This increased runoff, in addition to eroding and degrading the land that it flows over, also causes major disruption to surrounding watersheds by altering the volume and rate of water that flows through them, and filling them with chemically polluted sedimentation. The increased flow of water through local waterways also causes a large increase in the rate of bank erosion.BOOK, James, William, Channel and habitat change downstream of urbanization, Herricks, Edwin E., Jenkins, Jackie R., Stormwater Runoff and Receiving Systems: Impact, Monitoring, and Assessment, CRC Press, 1995, 978-1-56670-159-4, 105,weblink Climate change The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.WEB, Intergovernmental Panel on Climate Change (IPCC), 1995, Second Assessment Synthesis of Scientific-Technical Information relevant to interpreting Article 2 of the UN Framework Convention on Climate Change, 5,weblink 2015-10-05,weblink" title="web.archive.org/web/20130309040926weblink">weblink 2013-03-09, dead, The rise in sea levels that has occurred as a result of climate change has also greatly increased coastal erosion rates.BOOK, Bicknell, Jane, etal, Adapting Cities to Climate Change: Understanding and Addressing the Development Challenges, Earthscan, 2009, 978-1-84407-745-8, 114,weblink For an overview of other human activities that have increased coastal erosion rates, see: BOOK, Goudie, Andrew, Accelerated coastal erosion, The Human Impact on the Natural Environment, MIT Press, 2000, 978-0-262-57138-8, 311,weblinkweblink (File:Ghana Flooding 2.jpg|thumb|Most part of Accra mostly flooded during rainy season, causing environmental crisis in Ghana)Studies on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of soil erosion. Thus, if rainfall amounts and intensities increase in many parts of the world as expected, erosion will also increase, unless amelioration measures are taken. Soil erosion rates are expected to change in response to changes in climate for a variety of reasons. The most direct is the change in the erosive power of rainfall. Other reasons include: a) changes in plant canopy caused by shifts in plant biomass production associated with moisture regime; b) changes in litter cover on the ground caused by changes in both plant residue decomposition rates driven by temperature and moisture dependent soil microbial activity as well as plant biomass production rates; c) changes in soil moisture due to shifting precipitation regimes and evapo-transpiration rates, which changes infiltration and runoff ratios; d) soil erodibility changes due to decrease in soil organic matter concentrations in soils that lead to a soil structure that is more susceptible to erosion and increased runoff due to increased soil surface sealing and crusting; e) a shift of winter precipitation from non-erosive snow to erosive rainfall due to increasing winter temperatures; f) melting of permafrost, which induces an erodible soil state from a previously non-erodible one; and g) shifts in land use made necessary to accommodate new climatic regimes.JOURNAL, Klik, A., Eitzinger, J., October 2010, Impact of climate change on soil erosion and the efficiency of soil conservation practices in Austria,weblink The Journal of Agricultural Science, en, 148, 5, 529–541, 10.1017/S0021859610000158, 2010EGUGA..12.5412K, 86550618, 0021-8596, Studies by Pruski and Nearing indicated that, other factors such as land use unconsidered, it is reasonable to expect approximately a 1.7% change in soil erosion for each 1% change in total precipitation under climate change.JOURNAL, Pruski, F. F., M. A., Nearing, 2002, Runoff and soil loss responses to changes in precipitation: a computer simulation study, Journal of Soil and Water Conservation, 57, 1, 7–16,weblink In recent studies, there are predicted increases of rainfall erosivity by 17% in the United States,JOURNAL, Nearing, M. A., Pruski, F. F., O'Neal, M. R., 2004-01-01, Expected climate change impacts on soil erosion rates: A review,weblink Journal of Soil and Water Conservation, en, 59, 1, 43–50, 0022-4561, by 18% in Europe,JOURNAL, Panagos, Panos, Ballabio, Cristiano, Meusburger, Katrin, Spinoni, Jonathan, Alewell, Christine, Borrelli, Pasquale, Towards estimates of future rainfall erosivity in Europe based on REDES and WorldClim datasets, Journal of Hydrology, 548, 251–262, 10.1016/j.jhydrol.2017.03.006, 28649140, 5473165, 2017, 2017JHyd..548..251P, and globally 30 to 66%JOURNAL, Borrelli, Pasquale, Robinson, David A., Panagos, Panos, Lugato, Emanuele, Yang, Jae E., Alewell, Christine, Wuepper, David, Montanarella, Luca, Ballabio, Cristiano, 2020-09-08, Land use and climate change impacts on global soil erosion by water (2015-2070), Proceedings of the National Academy of Sciences, en, 117, 36, 21994–22001, 10.1073/pnas.2001403117, 0027-8424, 32839306, 7486701, 2020PNAS..11721994B, free, Global environmental effects (File:Runoff and filtersoxx.ogv|left|thumb|468x468px|run-off and filter soxx)(File:Water erosion map.jpg|thumb|325px|World map indicating areas that are vulnerable to high rates of water erosion)File:Rano Raraku quarry.jpg|thumb|During the 17th and 18th centuries, Easter Island experienced severe erosion due to deforestation and unsustainable agricultural practices. The resulting loss of topsoil ultimately led to ecological collapse, causing mass (starvation]] and the complete disintegration of the Easter Island civilization.JOURNAL, Dangerfield, Whitney, The Mystery of Easter Island, Smithsonian Magazine, April 1, 2007,weblink BOOK, Montgomery, David, Islands in time, Dirt: The Erosion of Civilizations, University of California Press, October 2, 2008, 1st, 978-0-520-25806-8,weblink )Due to the severity of its ecological effects, and the scale on which it is occurring, erosion constitutes one of the most significant global environmental problems we face today.BOOK, Toy, Terrence J., Soil Erosion: Processes, Prediction, Measurement, and Control, John Wiley & Sons, 2002, 978-0-471-38369-7, 1,weblink etal, Land degradation Water and wind erosion are now the two primary causes of land degradation; combined, they are responsible for 84% of degraded acreage.Each year, about 75 billion tons of soil is eroded from the land—a rate that is about 13–40 times as fast as the natural rate of erosion.BOOK, Zuazo, Victor H.D., Pleguezuelo, Carmen R.R., amp, Soil-erosion and runoff prevention by plant covers: a review, Lichtfouse, Eric, etal, Sustainable agriculture, Springer, 2009, 978-90-481-2665-1, 785,weblink Approximately 40% of the world's agricultural land is seriously degraded.NEWS, Sample, Ian, Global food crisis looms as climate change and population growth strip fertile land, The Guardian, August 30, 2007,weblink According to the United Nations, an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation and climate change.NEWS, Smith, Kate, Edwards, Rob, amp, 2008: The year of global food crisis, The Herald (Scotland), March 8, 2008,weblink In Africa, if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.WEB,weblink news.mongabay.com, Africa may be able to feed only 25% of its population by 2025,weblink" title="web.archive.org/web/20061216080905weblink">weblink 2006-12-16, 2006-12-14, Recent modeling developments have quantified rainfall erosivity at global scale using high temporal resolution (