The water cycle is the movement of water from the surface of the Earth into the sky and atmosphere and back again to the surface of the Earth. The water cycle is continuous and is a large part of what we call weather and climate.
Here’s how the water cycle works: Liquid water collects in rivers, lakes, and oceans. Energy from the Sun heats the water and changes into a gas called water vapor. This process is called evaporation. Water vapor rises high into the sky and as it rises in the atmosphere it cools. This is called condensation. Water vapor that cools forms clouds. Wind blows clouds through the sky essentially moving water from here to there. When tiny water droplets in clouds collide, they form bigger droplets. When water droplets become so big and heavy that a cloud can no longer hold them, they fall to the Earth as rain, snow, hail, or sleet. This is called precipitation. Most of the precipitation that falls to the Earth gathers again in rivers, lakes, and oceans. This is called collection.
The water cycle–the collection, evaporation, condensation, and precipitation of water–is a continuous exchange of moisture between the oceans, the atmosphere, and the land. The water cycle has been happening almost since the Earth was formed billions of years ago. The cycling of water in and out of the atmosphere is a very important aspect of the weather patterns on Earth. Water on the ground, in the air, and in lakes and oceans (or the lack of water) highly determines climates around the world.
Water makes up about 75 percent of the Earth’s surface. Geologic evidence suggests that large amounts of water have flowed on Earth for the past 3.8 billion years—most of the planet’s existence. Water is an essential ingredient for the development and nourishment of life. Water vapor is a powerful greenhouse gas; it soaks up the Sun’s heat and carries it around in clouds. Besides weather, climates around the Earth are greatly determined by the water cycle.
Weather is what is happening in the short term where you are–the next few minutes to the next few months. Climate is the long-term weather patterns in a particular region, that is predictable patterns of weather over years and decades. A climate can be mostly wet (such as tropical rainforests) or mostly dry (such as deserts) or somewhere in between. Climate and climate change impact human life and all life on Earth. Climate and how life happens is very much determined by the water cycle.