The water cycle is a cycle that causes the cycling flow of water in different forms and both up, below and at the earth surface. We know, water can be present at three stages such as: solid, liquid and gaseous. These all forms are seen in the water cycle where processes like precipitation, evaporation, condensation take place.
Some info about water and water cycle:
- Total water stored on earth’s surface 1.4 × 109 km3.
- The water cycle is also called ‘The Hydrological cycle’.
How the water was formed?
Geoscientists opined that water formed via primary degassing of ejected magma from volcanoes abundant during prehistoric period of earth. The rate of degassing was about 167 km3/year.
Inquiring into specifics:
The scientists were baffled many times by the origin and evolution of the earth and mostly its liquid hydrosphere. Luckily, many of the problems have been solved by our modern scientists. But the origin of water took a toll on them as they swinged in ideas that either the water came from the comets hitting earth or from within the earth itself.
A study in recent years have assured that it was the magma within the earth not the comets who were responsible for this vast hydrosphere that covers about 71% of earth surface.
Evidence suggests that water is stored in the Earth’s mantle in the form of hydroxyl groups (OH-) (one hydrogen and one oxygen atom) trapped within minerals such as ringwoodite.
When the mantle melts, the water in the minerals dissolves into the magma. As the magma rises towards the surface through the mouth of the volcanoes and cools itself, the water is released as water vapor. The decrease in pressure helps in its evaporation process. And then enters into the water cycle. This mechanism is a great way of water to be degassed from the earth’s interior to the surface world.
Three steps of water cycle
- Evaporation and transpiration
- Surface flow and percolation (liquid passing through a filter)
The future of water as a resource
Water is a resource to every life form on earth. Especially the human race is mostly dependent on it. It should be noted here that though there is a lot of water in the water sphere, a minute fraction of it is available to humans and this fraction is getting polluted day by day. That means our water resource is not an infinite supply rather its utility is decreasing like any other resource though maintaining the same quantity as before.
The table below shows water as a resource and its availability in different forms that might help us interpreting its future.
|Source||Volume×103 km3||% of total||% of total only for freshwater||Renewal time|
|P. ice + glaciers||29000||2.08||87.21||16000 years|
|FW Lakes||125||0.009||0.377||1-100 years|
|S. Lakes||104||0.008||–||10-1000 years|
|Soil moisture||67||0.005||0.209||280 years|
|Atmos. vapor||14||0.0009||0.037||9 days|
- Total volume of hydrosphere of 1.4 × 109 km3.
- 87.21% stored in polar ice caps and glaciers.
- 12.5% underground.
- 0.377% is deposited in freshwater lakes.
- Rivers contain 0.0037%.
- Atmospheric water vapor (0.037%) shortest renewal time i.e., 9 days.
- Polar water has longest renewal time i.e. 16,000 years.
- Easily available – water of precipitation amounts 38,600 km3/year.
The water budget table
|Use||Rate in liter/day/head|
On an average each human being requires ca. 2000 liter or 2 m3 water per day.
As per 1976 world population (4×109), total water required globally [2×(4×109)] = 8×109 m3/day. or, 8 km3/day (because 1 km3 = 109 m3) or (365×8) = 2920 km3/year
Available water 38600 km3/year
So, (38600÷2920) = 13 times more population would be required to consume this water.
i.e., population size of (13×4×109) = 52×109 could be supported.
When that time will come?
Scientists estimated that world’s population gets doubled in every 30 years. So, with this rate, after 110 years, available freshwater will not be sufficient. However, crisis in freshwater may hit much before than that time because:
- population density and precipitation not distributed uniformly over the globe, high demand of water prevails in arid regions and developed nations.
- not all flowing freshwater is usable.
- use and demand of freshwater very high in rapidly growing urban areas and in dry countries.
- all naturally available freshwater not qualitatively good. Polluted water means unavailability of water.
I hope this article would help you with various details and info about the water on earth. Moreover, the water budget calculation might give you an insight of the water crisis that we may face in near decades or middle of the century.