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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The water cycle describes how water moves through Earth's land, oceans and atmosphere. Water always exists in all three places, in many forms. It is in lakes and riversglaciers and ice sheets, oceans and seas. It is also found underground and as a gas in the air and 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. In the water cycle, liquid water in the ocean, lakes or rivers evaporates. When it evaporates, it becomes water vapor. Water vapor is an invisible gas.

Evaporation is driven by the sun. The sun warms up the water on the surface of the ocean. The molecules that make up water start moving around quickly and spread apart. The liquid water then turns into an invisible gas. Evaporation is also helped by wind and air temperature.


Condensation is when gas changes to a liquid. In the water cycle, water vapor in the atmosphere condenses. The gas molecules that were once warm and moving apart quickly become cooler and move closer together. This causes the vapor to become liquid. Clouds can form as water vapor condenses.


Precipitation is any liquid or solid water that falls to Earth after condensation happens in the atmosphere. Rain, snow and hail are all precipitation.

Precipitation is how water is cycled from the atmosphere to the Earth.

States Of Water

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

Ice is solid water. Most of Earth's freshwater is ice, locked in giant glaciers, ice sheets and ice caps.

Ice turns into a liquid when it melts. The ocean, lakes and rivers all hold liquid water, and it is also found underground.

The amount of water vapor in the atmosphere is different across the Earth. There is a lot in the air above the ocean, but there is less in the deserts because there is less water there.

The Water Cycle And Climate

The water cycle has a big influence on Earth's climate and ecosystems.

Climate is all the weather conditions of a specific area. Humidity is a weather condition that has an effect on climate.

Humidity is the amount of water vapor in the air. Because water vapor is not evenly spread across the atmosphere, some places have higher humidity than others. This is why there are very different climates on Earth. Islands or coastal regions, like Florida or Hawaii, are usually very humid. Water vapor makes up a large part of the atmosphere in these areas. Inland regions with deserts, like Arizona, are usually not humid at all. That is because there is very little water vapor in the atmosphere.

The Water Cycle And The Landscape

The water cycle also influences the physical geography of the Earth. Glacial melt and erosion are two of the ways the water cycle changes the land.

As glaciers slowly expand, they can carve away entire valleys and create mountain peaks. They can leave behind rubble as big as boulders. The Matterhorn is a famous mountain peak between Switzerland and Italy. It was created when glaciers smashed together and squeezed up the earth between them.

Glacial melt can also create landforms. The Great Lakes, for example, are found in the Midwest of the United States and Canada. They were created when an enormous ice sheet melted and moved back, leaving liquid pools.

Erosion is when water wears away part of the land. For example, the flow of water can help carve enormous canyons. These canyons, like the Grand Canyon, can be carved by rivers. They can also be carved by currents deep in the ocean.

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.

Media Credits

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

October 19, 2023

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