Soil Erosion

Soil erosion is when soil is washed or blown away faster than it can be replaced. A small amount of natural erosion is normal: rivers cut canyons, wind shapes sand dunes, frost slowly weathers mountainsides. But when humans cut down forests, plough wide fields and let bare soil sit exposed to the weather, erosion can speed up dramatically. The world is currently losing roughly 1% of its farmable soil every year: a slow disaster that takes generations to notice but ruins land for centuries. Stopping soil erosion is one of the most important environmental jobs on Earth.

• Global soil lost per yearApprox. 24 billion tonnesAbout 3 tonnes per person
• % of farmland lost yearlyApprox. 1%Adds up fast over decades
• Time to replace 1 cmApprox. 100 yearsBut erosion can lose it in a single storm
• Main causesWater, wind, farmingPlus overgrazing and deforestation
• Famous disasterDust Bowl, 1930s USAForced millions of farmers off the land
• Best defencePlant rootsTrees, grass, cover crops

What causes soil erosion

• Water erosion: heavy rain hits exposed soil and either washes it away in sheets or cuts deep gullies through it. Most common on sloping land.
• Wind erosion: dry, bare soil is picked up by strong wind and blown away. Most common in dry climates.
• Tillage erosion: ploughing and digging gradually move soil downhill, especially when fields are ploughed up and down a slope instead of across it.
• Mass movement: whole chunks of soil and rock slide downhill at once, in landslides or mudslides.

What makes erosion worse

Human activities have dramatically sped up natural erosion in many parts of the world.

• Deforestation: cutting down trees removes the roots that hold soil in place and the leaves that protect it from rain.
• Overgrazing: too many sheep, cattle or goats eat all the grass, leaving bare soil for the wind and rain to attack.
• Ploughing: especially when fields are bare for long periods between crops, or when ploughing is done up-and-down hills.
• Building: roads, houses and quarries strip away the surface soil.
• Climate change: more extreme storms, droughts and floods all worsen erosion.

The American Dust Bowl

The most dramatic case of human-caused soil erosion happened in the 1930s on the American Great Plains. For decades, farmers had been ploughing up the natural prairie grass to grow wheat. When a severe drought hit between 1931 and 1939, the bare soil dried out and a series of enormous dust storms (some carrying topsoil 2,000 km east to Washington, DC) blew away millions of hectares of soil.

The disaster became known as the Dust Bowl. Tens of thousands of farms were ruined. Approximately 2.5 million people abandoned their homes and migrated west looking for work (a story told in John Steinbeck's novel The Grapes of Wrath). It took decades of careful soil conservation work, plus a return of normal rainfall, before the area recovered. The disaster led directly to the creation of the United States Soil Conservation Service, the world's first national soil protection agency.

Fact A single hectare of bare ploughed field can lose over 50 tonnes of soil per year to rain and wind. The same hectare, kept under cover crops or grass, might lose less than 1 tonne. The difference is roughly the difference between losing 1 cm of topsoil every 5 years and losing it every 250 years.

How farmers stop erosion

Modern farmers and land managers have many techniques for protecting soil.

• Cover crops: planting fast-growing plants (often clovers or ryegrass) over winter to keep the soil covered.
• Contour ploughing: ploughing across slopes instead of up and down, so water cannot run straight downhill.
• Terracing: building flat steps into steep hillsides. Used for centuries by farmers in the Andes, the Philippines and the Mediterranean.
• Crop rotation: changing the crop in each field every year to keep the soil healthy and prevent pests.
• Windbreaks: rows of trees and hedges around fields to slow the wind.
• No-till farming: planting seeds directly into uncut ground without ploughing. Keeps soil structure intact.
• Restoring wetlands and woodlands: trees and bogs hold soil in place better than almost anything else.

Did you know? The Loess Plateau in northern China was once one of the most eroded places on Earth, with deep gullies cutting through a barren landscape. Starting in the 1990s, China carried out one of the world's biggest soil restoration projects, terracing hillsides and planting millions of trees. Over 20 years, an area the size of Belgium was transformed from desert into green farmland again. It is one of the greatest examples of how soil can come back if humans put in the work.

Deeper dive: why soil loss is a slow-motion crisis

Soil erosion is a particularly difficult problem because it tends to happen slowly enough that nobody notices until it is too late. A field losing 1 mm of topsoil a year is losing a worrying amount of soil in scientific terms (around 13 tonnes per hectare per year) but is impossible to see by eye. Decades later, that adds up to losing the entire top 30 cm of fertile soil, and farmland that took 30,000 years of nature to build can be ruined in a single human lifetime.

This is why scientists call soil a finite resource, even though it can technically be made by nature. The replacement rate (approx. 1 cm per 100 years in most places) is so slow compared to the loss rate that any soil eroded today is essentially gone for human purposes.

The good news is that humans have invented many techniques that work. Whole communities have rescued their farmland using terracing, cover crops, tree planting and careful livestock management. The Loess Plateau restoration in China, the Tigray restoration in northern Ethiopia and many regenerative farms in the United States, Australia and Europe show that soil can come back even after major damage. But it requires sustained effort over decades.

One of the United Nations Sustainable Development Goals (15.3) is to achieve "land degradation neutrality" by 2030: gaining as much healthy soil as we lose. As of 2025, the world is still losing soil far faster than it is being restored, but the awareness and the techniques to fix it are now widely understood.

For more, see composting and types of soil.