Soil erosion is the process of removing or wearing away the top layer of soil. It is a type of soil damage. This natural process happens because of the movement caused by different forces, such as water (like landslides or floods), ice (like glaciers), snow (like avalanches or snow sliding), air (like wind), plants (like uprooted trees), and animals, including humans. Based on these forces, erosion is sometimes grouped into types, such as water erosion, glacial erosion, snow erosion, wind erosion, erosion caused by animals, and erosion caused by human activities, such as farming. Soil erosion can happen slowly and go unnoticed, or it can occur quickly, leading to the loss of valuable topsoil. Losing soil from farmland can reduce the size of farmland, lower crop production, harm water quality, and damage drainage systems. Soil erosion can also create sinkholes and soil tunnels that may grow into small channels and gullies.
Human activities have increased the rate of erosion worldwide by about 28 times compared to natural erosion. Too much erosion causes problems both where it happens and in other areas. Local effects include lower agricultural productivity and, in natural areas, the breakdown of ecosystems, because the rich topsoil layers are lost. In some cases, this can lead to desert-like conditions. Effects elsewhere include dirt blocking waterways, making water bodies too rich in nutrients, and damaging roads and buildings. Water and wind erosion are the main causes of land damage; together, they affect about 84% of the world’s degraded land, making excessive erosion one of the most serious environmental issues globally.
Activities such as heavy farming, cutting down forests, building roads, acid rain, human-caused climate changes, and expanding cities are major human activities that increase erosion. However, there are many ways to prevent or reduce erosion of vulnerable soils.
Physical processes
When soil is completely soaked or when rain falls faster than the soil can absorb water, surface runoff happens. If the runoff has enough energy, it can carry loose soil particles (sediment) down slopes. Rainfall and the runoff it creates cause four main types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. Splash erosion is the first and least severe stage of soil erosion. It is followed by sheet erosion, then rill erosion, and finally gully erosion, which is the most severe.
During splash erosion, raindrops hit the ground and create small craters, sending soil particles flying. These particles can travel up to 0.6 meters (two feet) vertically and 1.5 meters (five feet) horizontally on flat ground without wind.
Sheet erosion happens when loose soil particles are moved by water flowing over the land’s surface.
Rill erosion forms small, temporary water channels on slopes that act as both sources and paths for soil movement. These channels are usually shallow, with slopes that can be very steep. Unlike rivers and streams, rills have different water movement patterns because of their size and depth.
Gully erosion occurs when water collects and flows quickly through narrow channels after heavy rain or melting snow, removing soil to great depths. Grazing can also cause gully erosion by compacting the soil, reducing its ability to absorb water and increasing erosion in vulnerable areas.
Valley or stream erosion happens when water flows continuously along a linear path. This erosion deepens valleys downward and extends them backward into hillsides, creating steep banks and head cuts. In the early stages, erosion is mostly vertical, forming V-shaped valleys with steep slopes. Later, erosion becomes horizontal, widening the valley floor and creating floodplains. During floods, more water and faster movement increase erosion. Sediments and rocks carried by the water also contribute to erosion through a process called traction.
Bank erosion is the wearing away of the sides of streams or rivers. This is different from changes to the riverbed, which is called scour. Scientists measure bank erosion by placing metal rods in the bank and marking where the bank surface is at different times.
Thermal erosion happens when moving water melts and weakens permafrost. This can occur near rivers and coasts. For example, the Lena River in Siberia shows rapid channel movement due to thermal erosion, as its banks are made of non-cohesive permafrost materials. Large slumps of weakened soil often collapse. Thermal erosion also affects Arctic coasts, where waves and warm water undercut permafrost cliffs, causing them to collapse. Between 1955 and 2002, erosion along a 100-kilometer (62-mile) stretch of the Beaufort Sea shoreline averaged 5.6 meters (18 feet) per year.
At very high water flows, large whirlpools called kolks form. These whirlpools cause intense erosion, removing bedrock and creating rock-cut basins. Examples of this can be seen in the Columbia Basin region of Washington, where floods from glacial Lake Missoula carved the channeled scablands.
Wind erosion is a major force shaping the land, especially in dry areas. It causes land degradation, desertification, dust, and crop damage, often worsened by human activities like deforestation, farming, and urban growth. Wind erosion has two main types: deflation, where wind removes loose particles, and abrasion, where wind-blown particles wear down surfaces. Deflation has three forms: surface creep (larger particles rolling on the ground), saltation (particles bouncing just above the ground), and suspension (very small particles carried far by wind). Saltation causes about 50–70% of wind erosion, suspension causes 30–40%, and surface creep causes 5–25%. Silty soils, like loess, are most affected by wind erosion because their particles are easily moved.
Wind erosion is more severe in dry areas and during droughts. For example, in the Great Plains, wind erosion can remove up to 6,100 times more soil during drought years than in wet years.
Mass movement is the downward and outward movement of rock and soil on slopes, mainly due to gravity. It plays a key role in breaking down and moving weathered materials in mountainous areas. Mass movement can be slow or sudden, sometimes causing landslides. A slow type of mass movement is a scree slope, where loose rock accumulates at the base of a slope.
Slumping occurs on steep hillsides, often in clay-rich materials. It can happen when water weakens the soil or when poor engineering causes slopes to collapse. Slumps often form a spoon-shaped depression as material moves downhill.
Surface creep is the very slow movement of soil and rock by gravity, usually only noticeable over long periods. It can also describe the rolling of tiny soil particles (0.5 to 1.0 mm in size) along the ground by wind.
Tillage erosion happens in farmland when farming tools move soil. Evidence shows that tillage erosion is a major cause of soil loss in agricultural areas, sometimes exceeding erosion from water and wind.
Factors affecting soil erosion
The amount and strength of rainfall is the main weather factor that affects soil erosion by water. This connection is strongest when heavy rain happens at times or places where the soil is not protected by plants. This can occur during farming seasons when the soil is left uncovered, or in dry areas where plants naturally grow sparsely. Wind erosion happens when strong winds blow during droughts, when plants are sparse and the soil is dry and easier to move. Other weather factors, like average temperature and how much temperatures change, can also influence erosion by affecting plants and soil properties. In general, areas with more rainfall (especially heavy rain), stronger winds, or more storms tend to have more erosion, assuming similar plant life and ecosystems exist.
In some parts of the world, such as the Midwestern United States and the Amazon Rainforest, the strength of rainfall is the main factor that determines how much erosion happens. Raindrops that are larger and fall faster have more energy, which can move soil particles farther than smaller, slower raindrops.
In other areas, like western Europe, erosion happens when light, steady rainfall falls on soil that is already very wet. In these cases, the total amount of rain, not its strength, is the main factor that affects how much erosion occurs.
Soil texture, how wet it is, and how tightly packed it is also play a major role in how much erosion happens. Soils with more clay are usually harder to erode than those with sand or silt, because clay helps hold soil particles together. Soils with more organic matter are also harder to erode, because organic materials help soil particles stick together, making the soil stronger. How much water is already in the soil before rain falls also matters, because it limits how much new water the soil can absorb. If the soil is already very wet, it cannot take in as much rain, leading to more runoff and more erosion. Soil that is pressed tightly together (compacted) allows less water to soak in, increasing runoff and erosion.
Plants act as a link between the air and the soil. They help water move into the soil, reducing runoff. They also protect the soil from wind, which reduces wind erosion and improves the local climate. Plant roots hold soil particles together, creating a stronger, more stable structure that is less likely to erode. Removing plants increases the speed of soil erosion.
The shape of the land affects how quickly water flows over the surface, which influences how much erosion happens. Long, steep slopes (especially those without enough plant cover) are more likely to erode quickly during heavy rain than short, gentle slopes. Steeper areas are also more likely to experience landslides, mudslides, and other types of erosion caused by gravity.
Human activities that aid soil erosion
Unsustainable farming methods increase erosion rates by 10 to 100 times compared to natural erosion and far exceed the rate at which new soil forms. Plowing soil into smaller pieces is a major cause of this problem. Modern machines allow deep plowing, which makes more soil available for erosion by water. Other causes include planting the same crop repeatedly, farming on steep slopes, using pesticides and fertilizers (which harm soil-holding organisms), row planting, and surface irrigation. Soil erosion events can lead to complex issues with nutrient loss because smaller soil particles, like those containing phosphorus, are more likely to be lost than larger ones. These smaller particles may have less phosphorus, which affects water quality. Plowing also increases wind erosion by drying the soil and breaking it into tiny pieces that wind can carry. Removing trees from farmland allows wind to move faster over open areas, worsening erosion. Heavy grazing reduces plant cover and compacts soil, both of which increase erosion.
In forests, the top layer of soil is protected by leaf litter and humus, which form a soft, porous layer that absorbs raindrops. This layer slows water from running off the surface and allows it to soak into the ground. Tree roots and fungi help hold soil together, preventing it from washing away. Plants also reduce the speed of falling raindrops, lowering their energy before they hit the ground. However, the forest floor, not the tree canopy, is most important in preventing erosion. Raindrops reach their maximum speed after falling about 8 meters (26 feet). Since tree canopies are usually higher than this, raindrops can regain speed after hitting the canopy. The forest floor, with its layers of leaves and organic matter, still absorbs the impact of rain.
Deforestation increases erosion by exposing soil to the air, removing the protective layers of humus and litter, and compacting soil from logging equipment. If the forest floor remains intact after trees are removed, erosion may be low. However, severe fires can cause more erosion if heavy rain follows.
One of the biggest causes of soil loss worldwide is the slash-and-burn method used in tropical forests. For example, in Madagascar’s high central plateau, much of the land has no plants, with deep gullies up to 50 meters (160 feet) deep and 1 kilometer (0.6 miles) wide. Shifting cultivation, which sometimes uses slash-and-burn, harms soil fertility over time. Some debate whether slash-and-burn farming with short-term use and forest regrowth is better than long-term farming that destroys forests. Studies in Brazil show that after a few years of regrowth, erosion from slash-and-burn areas decreases to levels similar to natural forests. Another study found that 15 years of rest after farming can restore soil conditions.
Human activities greatly affect erosion. Clearing land removes plants, changes water flow, and compacts soil during construction. Covering land with asphalt or concrete increases runoff and wind speed. Sediment from urban areas, like roads, is often polluted with fuel and oil. This runoff damages land and disrupts water systems by changing water flow and adding polluted sediment. Increased water flow also erodes riverbanks faster.
Warmer temperatures are expected to increase rainfall intensity and sea levels, leading to more erosion. Studies show that more rain and stronger storms will increase soil erosion unless steps are taken to prevent it. Erosion rates may change due to: (a) changes in plant cover from altered rainfall; (b) changes in leaf litter from temperature and moisture affecting soil microbes; (c) changes in soil moisture affecting how water soaks into the ground; (d) reduced soil organic matter making soil easier to erode; (e) more rain instead of snow in winter; (f) melting permafrost creating erodible soil; and (g) changes in farming practices due to climate shifts.
Studies by Pruski and Nearing suggest that, without considering land use, soil erosion may increase by about 1.7% for every 1% increase in rainfall. Early 21st-century studies predicted a 17% rise in rainfall erosivity in the U.S., 18% in Europe, and 30–66% globally by the end of the century.
Global environmental effects
Soil erosion is a major global environmental problem. It has serious effects on the environment and happens on a large scale. Water and wind erosion are the main causes of land degradation. Together, they are responsible for 84% of land that has been damaged. Each year, about 75 billion tons of soil are lost from the land. This happens at a rate that is 13 to 40 times faster than the natural rate of erosion. About 40% of the world's farmland is seriously degraded. 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. In Africa, if current soil degradation trends continue, the continent might only be able to feed 25% of its population by 2025, according to the United Nations University's Institute for Natural Resources in Africa.
Scientists have developed models that measure how rainfall causes erosion worldwide. These models use detailed rainfall data recorded at very short time intervals. A global effort to collect data created the Global Rainfall Erosivity Database (GloREDa), which includes information from 3,625 stations in 63 countries. This database was used to create a map showing erosion risk across the world. A study published in Nature Communications found that about 36 billion tons of soil are lost each year because of water erosion and changes in land use, such as deforestation. The study used high-resolution models to examine soil erosion patterns globally. This method allows scientists to include details about land use, farming areas, and how different farming practices affect erosion.
Soil loss from erosion is a problem because people often respond by using chemical fertilizers. This can cause more pollution in water and soil, instead of letting the land recover naturally. Soil erosion, especially from farming, is the leading cause of water pollution worldwide. This happens because too much sediment from eroded soil flows into rivers and lakes. The sediment itself is a pollutant and can carry other harmful substances, like pesticides or heavy metals.
Too much sediment in water can harm aquatic ecosystems. It can cover fish spawning areas, reduce their food supply, and block their gills, causing breathing problems. It also harms plants, algae, and small animals that live in water. Even though sediment events may be short, the damage to ecosystems can last for a long time.
Before the 1980s, one of the worst erosion problems in the world was in China, along the middle part of the Yellow River and the upper part of the Yangtze River. Every year, over 1.6 billion tons of sediment from the Yellow River flow into the ocean. This sediment mainly comes from erosion in the Loess Plateau region of northwestern China.
Wind erosion also causes air pollution. Dust from eroded soil becomes airborne and can carry harmful chemicals, such as pesticides or fuel. This dust can harm the environment and human health when it settles or is inhaled.
Dust from erosion can reduce rainfall and change the sky's color from blue to white, making sunsets appear redder. Dust events have been linked to the decline of coral reefs in the Caribbean and Florida since the 1970s. Similar dust from the Gobi Desert in Asia travels long distances and mixes with pollutants, reaching North America.
Monitoring, measuring and modelling soil erosion
Monitoring and modeling erosion helps people understand why soil erosion happens, predict how much erosion might occur under different conditions, and plan ways to stop or fix erosion problems. However, erosion processes are complex, and many scientific fields must be studied to understand and model them, such as climatology, hydrology, geology, soil science, agriculture, chemistry, and physics. Erosion models are also hard to calculate numerically because they are non-linear, which makes it difficult or impossible to use data from small areas to predict erosion in large regions.
The most common model for predicting soil loss from water erosion is the Universal Soil Loss Equation (USLE). This model was created in the 1960s and 1970s. It calculates the average annual soil loss (A) on a small plot of land using this formula:
A = R × K × L × S × C × P
In this formula, R represents rainfall erosivity, K is soil erodibility, L and S are topographic factors for length and slope, C is the cover and management factor, and P is the support practices factor.
Although the USLE was designed for small areas, it has often been used to estimate erosion on larger areas, such as watersheds, continents, and globally. A major issue is that the USLE cannot simulate gully erosion, so erosion from gullies is not included in USLE-based assessments. However, gully erosion can account for 10–80% of total erosion on farmland and grazed land.
Over the past 50 years, many other soil erosion models have been developed. However, because erosion processes are complex, all models can only roughly match real-world erosion rates when tested against actual measurements. This is why new models continue to be created. Some models, like the G2 model, are still based on USLE principles. Others, such as the Water Erosion Prediction Project model, have mostly or completely moved away from USLE elements. Many global studies still rely on the USLE.
For smaller areas, such as individual channels, dams, or spillways, erosion models use the critical shear stress of erosion and soil erodibility. These factors can be measured using geotechnical engineering methods like the hole erosion test or the jet erosion test.
Prevention and remediation
The most effective way to prevent erosion is to increase plant cover on the land. This helps stop erosion caused by wind and water.
Terracing is a very useful method for controlling erosion. People have used this technique for thousands of years in many parts of the world.
Windbreaks, also called shelterbelts, are rows of trees and shrubs planted along the edges of farmland. They protect crops from strong winds. In addition to reducing wind erosion, windbreaks improve growing conditions for crops, provide homes for helpful birds, help store carbon, and make farmland look better.
Traditional farming methods, such as growing different crops together instead of only one type and rotating crops each season, have been shown to reduce erosion.
Crop residues, such as leftover plant parts, help reduce erosion when used with conservation tillage. These residues protect soil from being broken apart by raindrops.
Erosion is more likely to happen when growing potatoes compared to cereals or oilseed crops. Forage plants, which have roots that spread out, help prevent erosion by holding soil in place and covering fields completely. In tropical coastal areas, mangroves have been studied as a way to reduce erosion. Their thick, tangled roots help protect against storm waves and floods, hold soil together, and slow water movement, which allows sediment to settle and reduces erosion. However, enough mangrove trees must be present to keep the balance of soil and sediment.
Agroforestry, which combines crops with trees, is a good way to reduce soil erosion, especially in tropical areas with heavy rains. It also helps in places where land has been damaged by heavy farming. Trees protect soil from wind and rain, reducing erosion caused by wind and water runoff.