Hydrologic Cycle

Hydrologic Cycle

The water cycle describes how water is exchanged (cycled) through Earth's land, ocean, and atmosphere.


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Earth Science, Meteorology, Geography, Physical Geography, Geology

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On Earth, water moves through the land, oceans and air. This is called the water cycle. Water always exists in all three places, in many forms. It is in lakes, glaciers, underground and in clouds.

Evaporation, Condensation And Precipitation

The water cycle is made up of three major parts: evaporationcondensation and precipitation.


Evaporation is when a liquid changes to a gas. A liquid is something that flows, like water in a river. It is not hard like a rock. A rock is a solid. In the water cycle, liquid water in the ocean, lakes or rivers evaporates and becomes water vapor. Water vapor is a gas that you cannot see. It goes up into the air into the atmosphere. The Earth is surrounded by a cloud of gases called the atmosphere.

Evaporation is driven by the sun. The sun warms up the water on the surface of the ocean. The tiny parts that make up water start moving around quickly and spread apart. The water turns into a gas.


Condensation is when gas changes to a liquid. This happens to water vapor in the atmosphere. The tiny parts of water vapor that were once warm and moving apart become cooler and move closer together. This causes the vapor to become liquid. Clouds can form during condensation.


Precipitation is a liquid or solid that falls to Earth. It falls after condensation happens in the atmosphere. Rain and snow are precipitation.

Precipitation is important in the water cycle. It is how water moves from the atmosphere to the Earth or ocean.

States Of Water

Through the water cycle, water continually rotates through three states: solid, liquid and vapor.

Ice is solid water. It is hard like a rock and does not flow. Most of Earth's freshwater is ice, locked in giant mountains of ice called glaciers. They are mainly found in the North and South Poles.

When ice melts it turns into a liquid. The ocean, lakes and rivers hold liquid water, and it is also underground.

The amount of water vapor in the atmosphere is different across Earth. There is a lot of water vapor in the air above the ocean. Very little vapor is above deserts because it is dry.

The Water Cycle And Climate

The water cycle has a big effect on Earth's climateClimate is what we call the weather that happens in an area. Humidity is one part of weather that affects climate.

Humidity is the amount of water vapor in the air. Some places have higher humidity than others. This is why there are very different climates on Earth. Think of islands or coastal areas, like Florida or Hawaii. These places are usually very humid. Water vapor makes up a large part of the atmosphere in these areas. Places with deserts, like Arizona, are not humid at all.

The Water Cycle And The Landscape

The water cycle also affects the shape of the Earth's surface.

As glaciers slowly grow, they can carve away entire valleys. They can also create mountains. Glaciers can push together and squeeze up the earth between them.

Glaciers can make giant lakes, too. The Great Lakes are found in between the United States and Canada. They were created when glaciers carved huge bowls into the land. Then enormous sheets of ice melted and filled the bowls.

Erosion is when water wears away part of the land. The flow of water can carve huge canyons, like the Grand Canyon.

Fast Fact

Breaking the Cycle
The water cycle can change. Glacial retreat is the process in which glaciers melt faster than their ice can be replaced by precipitation. Glacial retreat limits the amount of fresh water available on Earth. We are experiencing the fastest rate of glacial retreat in recorded history.

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Jeannie Evers, Emdash Editing, Emdash Editing
National Geographic Society
Last Updated

October 19, 2023

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