We explain what the water cycle is and its stages: evaporation, condensation, precipitation, infiltration, runoff. Also, its characteristics and importance.
What is the water cycle?
The water cycle (also known as the hydrological cycle) is the process of water circulation in the planet earth. During this cycle, water undergoes physical displacements and transformations (due to the action of factors such as cold and heat), and goes through the three states of matter: liquid, solid and gaseous.
It is made up of five stages (evaporation, condensation, precipitation, infiltration, runoff) during which water changes state in a continuous and unlimited cycle.
Water is one of the most abundant substances on the planet and covers most of the Earth. It can be found, in a liquid state, in oceans and seas; in solid state, in glaciers and polar caps; and, in the gaseous state, in water vapor. It is essential for life on Earth (all living beings need water to live and develop), and through its cycle, water circulates through the hydrosphere.
The water cycle is a biogeochemical cycle, that is, it is part of the cycles that in nature allow the movement and transformation of elements and chemical compounds through the biological, geological and chemical systems of the Earth. These cycles are essential to maintain the balance of ecosystems and life on the planet
Characteristics of the water cycle
Some of the characteristics of the water cycle are:
- It is made up of the processes of evaporation, condensation, precipitation, infiltration and runoff, during which water circulates in different states (liquid, solid and gaseous).
- It does not start at a specific point, but rather it is a continuity of processes (in which climatic elements, such as wind and solar energy, intervene) that are repeated successively.
- It is vital for the maintenance and stability of the planet.
- It is essential for the life of organisms.
- It regulates the climate, temperature and balance of the Earth's ecosystems.
Stages of the water cycle
The water cycle is made up of the following processes that happen successively:
1. Evaporation
The water cycle begins with the evaporation of water from the surface into the atmosphere. The liquid water in the oceans and other bodies of water evaporates and changes from a liquid to a gaseous state, due to the action of sunlight and the heat of the Earth. Plants also contribute to the evaporation process through their transpiration.
Since it is not possible to clearly distinguish between the amount of water that evaporates and the amount that is transpired by plants, the term “evapotranspiration” is often used to define the combined effect.
See also: Evaporation
2. Condensation
Water in the atmosphere moves, due to the action of the wind, in different directions, as water vapor.
Condensation takes place when water, in the form of vapor, reaches higher altitudes and low temperatures allow it to condense that is, recovering its liquid form and forming water droplets that accumulate in the clouds. Clouds become darker as they contain more water droplets.
See more in: Condensation
3. Precipitation
Precipitation occurs when water droplets in clouds become large and heavy. begin to fall towards the surface, attracted by the force of gravity and rain or precipitation occurs.
Water usually falls in liquid form, but in certain regions where temperatures are very low, it can fall in the form of snow.
See also: Precipitation
4. Infiltration
In infiltration, a part of the water that reaches the earth's soil infiltrates and becomes groundwater. The amount of water that percolates through the surface depends on different factors, such as the permeability of the soil, the slope and the vegetation cover of the region.
Once the water is infiltrated, circulates below the surface and moves underground. The infiltrated water circulates through the porous layers of rock, and is stored as groundwater, in the so-called “aquifers”. And part also circulates below the surface until it flows back into the oceans.
Groundwater is found in pores, between soil particles or in the cracks of rocks, and is an important reservoir of fresh water.
5. Runoff
Not all the water that falls as precipitation infiltrates into the subsoil. Runoff occurs when unabsorbed water moves across the surface. It does so from the highest areas to the lowest areas, pushed by the force of gravity.
Runoff also occurs when the sun melts the ice on top of mountains or in glaciers, causing a phenomenon called “thawing.”
Water that moves over the surface forms streams, rivers, ponds and lakes.
Importance of the water cycle
Water is the substance that allows life on planet Earth and it is thanks to its cycle that the amount of water available is maintained constantly and in continuous circulation. Thanks to this cycle, water is distributed throughout the planet.
The water cycle is a vital process because it determines that there is life on the planet and, in addition, it allows ecosystems to be preserved. The constant movement of water is responsible for regulating climates, distributing precipitation, modifying the temperature of the oceans, eroding land and transporting all types of substances from one place to another.
Thanks to this cycle, water is available to be used by living beings which obtain it from water courses or from the land. In addition, it allows humans to practice activities such as agriculture, livestock, mining and industry.
Of the total water in the world, only 3% is fresh water (which is what can be consumed by living beings) and the rest is salt water that comes from the oceans.
Environmental impact of alterations in the water cycle
The water cycle is a natural cycle that remains constant, which means that water cannot be created or eliminated: the planet always has the same amount of water that transforms and moves. However, there are human factors that can affect the correct functioning of this cycle.
Among the most prominent causes is climate change which is the increase in temperatures on Earth. This phenomenon causes a rise in the water temperature of rivers, lakes and seas, an increase in rainfall and droughts, the melting of glaciers and a rise in ocean levels. All of these consequences brought about by rising temperatures modify the way in which water is distributed on the planet.
There are other causes that affect the development of the cycle, among which are: indiscriminate felling of forests, soil erosion, water extraction and urbanization. These practices alter the normal hydrological cycle and bring consequences such as floods and droughts.
Because a very small percentage of available water is suitable for human consumption, Its scarcity and difficulty in obtaining are two aspects that must be taken into account. To achieve this, States must promote water management practices that aim to reduce consumption, avoid contamination and responsibly manage this resource so that it can be available to the world's population of the present and the future.
How is water distributed on planet Earth?
Water on the planet is distributed, according to its states, in the following way:
- In liquid state. 71% of the Earth's surface is covered by liquid water, of which 97% is salt water that forms the oceans. Only 3% is fresh water found in rivers, streams, lakes, ponds and aquifers.
- in solid state. A fraction of the water on Earth is in a solid state, that is, accumulated as ice. Glaciers and polar caps, located mainly in Greenland, on top of mountains, in Antarctica and in the Arctic Sea, occupy 10% of the planet's surface and represent 69% of available fresh water.
- in gaseous state. A minor fraction of water is in a gaseous state, as water vapor, and is part of the atmosphere.
References
- UNHCR (2018) The importance of water for life on the planet. United Nations High Commissioner for Refugees. United Nations Organization. https://eacnur.org/
- Tarbuck, E and Lutgens, F (2005) Earth Sciences. An introduction to physical geology. Prentice Hall.
- Vera, C and Camilioni, A (sf) The water cycle. Ministry of Education, Science and Technology of the Argentine Nation. http://www.bnm.me.gov.ar/
