The water cycle is also known as the hydrologic cycle. The water cycle describes the movement of water on, above and below the surface of Earth. Water can change states through the stages of the water cycle. Water can change from a solid to a liquid to water vapor in various places of the water cycle. Water moves from one lake to another, just like from an ocean to the atmosphere. Water travels by different processes of evaporation, condensation, precipitation, infiltration, runoff and subsurface flow. When these processes occur water goes through different phases such as: liquid, solid and gas.
Hydrologic cycle involves the exchange of heat energy, which leads to temperature changes. The process of evaporation where water takes up energy from the surroundings and cools the environment, however in the process of condensation water releases energy to its surroundings and warms the environment. When water moves from one place to another, the water cycle purifies water, replaces the Earth with fresh water and transports minerals to different places on the Earth. The water cycle also is involved with reshaping the Earths geological features of the Earth through processes like erosion and sedimentation.
The water cycle has an influence on climate as well. The sun is basically the motor to the water cycle. The sun heats oceans and seas and water from the heated oceans and seas evaporates as water vapor into the air. Ice and snow can sublimate right into water vapor. Rising air currents take the vapor up into the atmosphere where it condenses into clouds. Air currents move water vapor and cloud particles collide, grow and fall from the sky which is called precipitation. If precipitation gets cold enough it falls as snow or hail and sleet.
Most water accumulates back in the ocean or onto land as rain, where the water flows over the ground as surface runoff. Runoff and groundwater is stored in freshwater lakes. A lot of runoff soaks deep into the ground and fills up aquifers; which store water for long periods of time. Some groundwater finds openings in the ground and it comes out as fresh water springs. Over a period of time the water returns to the ocean where the water cycle starts. Groundwater can stay underground for over 10,000 years before leaving. Some water that has been underground for a long time is called fossil water.
Antarctica and Greenland are major ice sheets. These ice sheets store water for a very long time. Antarctica has been dated back around 800,000 years. The oceans supply about 90% of the evaporated water that goes into the water cycle. A lot of water is in storage for long periods of time than is actually moving through the water cycle. It is estimated that 95% of the world’s water is stored in the oceans. When it gets cold more ice caps and glaciers form and a lot of the global water supply accumulates as ice to make the amounts less in the water cycle. During the last ice age the oceans were 400 feet lower than they are today.
During the last “warm spell” the oceans were 18 feet higher than today. About three million years ago the oceans could have been up to 165 feet higher. It is predicted that the water cycle will intensify during the 21st century. Precipitation will not increase in all regions. In subtropical areas the precipitation is hypothesized that it will decrease during the 21st century. Some human activities can alter the water cycle. Some of these activities include : * Agriculture * Certain industry * Chemical composition in the atmosphere * Construction of dams * Deforestation and afforestation * Urbanization