The Water Cycle

The water cycle, also known as the hydrologic cycle, is the continuous movement of water on, above and below the surface of the Earth.

Water can change states among liquid, vapor, and ice at various places in the water cycle. Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go.

Water cycle is truly a "cycle," there is no beginning or end.

The heat of the sun warms everything on earth.  Moisture from all wet surfaces dries up.  This is called evaporation.  Liquid water changes to water vapor which then rises to form clouds.

The cold air in the sky changes the water vapor back to liquid water.  This process is called condensation.  The clouds keep on collecting condensed water vapor or droplets of moisture.  When the cloud becomes heavy with moisture, the small drops of moisture fall back to earth as rain.  Rain-water that falls on land flows back to the ocean.  The water cycle is then repeated.

Different Process

Precipitation – Condensed water vapor that falls to the Earth’s surface. Most precipitation occurs as rain, but also includes snow, hail, fog drip, graupel, and sleet.

Canopy interception – The precipitation that is intercepted by plant foliage and eventually evaporates back to the atmosphere rather than falling to the ground.

Snowmelt – The runoff produced by melting snow.

Runoff – The variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. As it flows, the water may infiltrate into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.

Infiltration – The flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.

Subsurface Flow – The flow of water underground. Subsurface water may return to the surface or eventually seep into the oceans. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.

Evaporation – The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration.

Sublimation – The state change directly from solid water to water vapor.

Advection – The movement of water in solid, liquid, or vapor states through the atmosphere. Without advection, water that evaporated over the oceans could not precipitate over land.

Condensation – The transformation of water vapor to liquid water droplets in the air, producing clouds and fog.

Transpiration – The release of water vapor from plants into the air. Water vapor is a gas that cannot be seen.

Simple Picture of Water Cycle

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Category: Earth Science