Atlas of the Biosphere

Water Cycle

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What is the water cycle?
Water covers more than two-thirds of the Earth. It is present in all of the living systems on the planet, and its transport drives weather patterns as well as climate in general.

How does it work?
Water can be stored in the atmosphere, above and below ground, the oceans, and inside living creatures. It enters the atmosphere through evaporation off the land and ocean surfaces, as well as by the transpiration of plants. Once in the atmosphere, water leaves the reservoir as precipitation in the form of snow or rain which falls on the land and ocean. Land precipitation can become ground water which travels below the land surface, or it can enter larger streams and rivers.

The Human Factor
Humans have been irrigating their farmland for thousands of years and with advances in technology, ground water is now available for this very purpose. However ground water isn't replenished as quickly as is surface runoff, with some reservoirs taking thousands of years to fill up. Especially in arid regions, where water is already scarce, irrigation using ground water is depleting the resource faster than it can be replaced. Thus, though it may be hard to believe, water isn't necessarily the limitless resource we once believed it to be.

Artwork by Maija Swanson and Nick Olejniczak