What is the water cycle?
The water cycle (also known as the hydrological cycle) is the process of water circulation on 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.
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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:
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
Water in the atmosphere moves, due to the action of the wind, in different directions, as water vapor.
Condensation occurs when water, in the form of vapor, reaches higher altitudes and low temperatures allow it to condense, that is, recover its liquid form and form water droplets that accumulate in clouds. Clouds become darker as they contain more water droplets.
Precipitation occurs when the water droplets contained in the 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
In infiltration, a part of the water that reaches the terrestrial 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, it circulates below the surface and moves through the subsoil. 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.
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 glaciers, causing a phenomenon called “thawing.”
Water that moves over the surface forms streams, rivers, ponds and lakes.