The water on Earth is always in movement, and the water cycle, also known as the hydrologic cycle, outlines the continuous movement of water on, above, and below the surface of the Earth.
The water cycle has no starting point. But for explanation purposes, we'll start in the oceans, because that is where most of Earth's water exists. The water cycle is driven primarily by the energy from the sun. The sun provides the energy that heats water in the oceans. This causes some of the water to evaporate as vapour into the air.
Additionally, the sun provides fuel for plants to carry out photosynthesis, the process which is responsible for transpiration. Rising air currents take the vapour up into the atmosphere, along with water from evapotranspiration, which is water transpired from plants and evaporated from the soil. The vapour then rises into the air where cooler temperatures cause it to condense into clouds. There are many different types of clouds, each with a unique shape and location in the sky.
Air currents move clouds around the planet. The cloud particles collide, grow, and fall out of the sky as precipitation. Precipitation refers to water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. Most of the water falls back into the oceans or onto land, where, because of gravity, the water flows over the ground as surface runoff. The water enters rivers in valleys in the landscape, with streamflow moving water towards the oceans. The water cycle is driven by various natural forces:
1. Sun: The sun provides the energy that causes water to evaporate. Additionally, the sun provides fuel for plants to carry out photosynthesis, the process which is responsible for transpiration.
2. Gravity: Gravity is the greatest force propelling the water cycle. It pulls water downhill and down from clouds and moves air and ocean water.
3. Chemical properties of water: Variations in water densities due to salinity and temperature contribute to the development of ocean currents.
4. Wind: The wind contributes to the formation of ocean currents, form surface waves, transport water through the sky via clouds and facilitates the process of evaporation by moving drier air over water.
5. Earthquakes: Earthquakes can displace enormous amounts of water.
6. Earth’s rotation: The Coriolis Effect makes currents of air travelling long distances around Earth appear to move at a curve as opposed to a straight line. The Coriolis Effect also makes huge storms rotate in different directions in the Northern and Southern Hemispheres.
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