Graphics and Animation by Olivier N.
The water cycle (also referred to as the hydrological cycle) is a model which represents exchanges (or flows) between major water reservoirs on the earth. When these flows occur, water is transformed through different states: solid, liquid and gaseous. Major reservoirs of water include oceans (largest storage), the atmosphere, fresh water entities (like lakes, rivers, swamps etc), underground water and glaciers.
The driving force (or engine) of the water cycle is the sun which enables water to evaporate and in turn leads to other forms of exchanges. The science that studies this cycle is called hydrology.
The water cycle in brief:
When solar energy emitted by the sun reaches the earth’s surface, it heats up water in different reservoirs (oceans, the atmosphere, lakes, rivers, swamps, ponds, trees, marshes etc). Due an increase in temperature, water vapor is generated and rises up into the atmosphere. Continuous accumulation of water in the atmosphere leads to saturation and condensation. Condensed water leads to precipitation which falls back on the earth’s surface as surface as rain, snow, fog, mist or hailstones. Once at the surface, some of the water flows as runoff into lakes, ponds, streams, valleys, marshes, rivers etc. Some of the water falls directly into the ocean and is stored. Water that does not move as runoff gets into the ground through the process of infiltration, with some reaching and circulating in underground water reserves through a process called percolation.
Water found on surface reserves later on gets into the atmosphere after heating and evaporation, setting the process once more in motion. Another way water leaves the earth’s surface is through evapotranspiration. This occurs when plants absorb water from underground sources through their roots. Some of the water is stored in plant tissues and used during photosynthesis meanwhile some is lost into the atmosphere during a process referred to as transpiration.
The water cycle is indispensable for the functioning of all ecosystems on earth since it ensures the constant presence and transfer of water at different levels. It is also a purifier and recycler of water.
Take an online water cycle quiz here >>>