Water cycle (or hydrological cycle) is the name given to the constant movement of water on Earth and in the atmosphere. This cycle has been going on for billions of years and is essential for life on our planet. With it, water not only changes its place, but also its physical state, varying between gaseous (when it evaporates), solid (when it freezes) and liquid states.
First, liquid water, present in oceans and rivers, evaporates. This water in a gaseous state becomes liquid again, forming rain clouds. With the rains, water returns to the cycle, whether falling on lakes, rivers and oceans, or falling on continents. The precipitation that occurs in the form of snow causes accumulation of ice, which can melt with the arrival of the warmer seasons.
Stages of the water cycle in nature
You can't say for sure where it starts. For didactic purposes, we are going to start explaining how the water cycle works from its evaporation.
Evaporation
When it receives heat from the Sun, the water on Earth undergoes the process of evaporation, changing from a liquid to a gaseous state. There is also evaporation of water from the soil and transpiration from plants (evapotranspiration). But most of the water that enters the cycle through evaporation (about 90%) comes from lakes, rivers and oceans. 87% of all evaporation comes from the oceans.
know more about evaporation.
Condensation
When it rises, carried by air currents, the steam cools and condenses. In other words: the water vapor becomes liquid again, forming clouds, which are nothing more than sets of very small particles of water in a liquid or solid state (ice).
know more about condensation.
Precipitation: rain, hail or snow
There comes a time when the water droplets join together, transforming into larger and larger drops. Clouds get very heavy. Due to the force of gravity, the drops fall in the form of rain.
It can happen that the air in the clouds is very cold (below 0°C). In that case, instead of raindrops, we will have ice crystals. If the air near the surface is also very cold, we may have, instead of a water storm, a blizzard, forming layers of ice on the Earth's surface. With the arrival of warm seasons, ice can melt or sublimate – that is, go straight from a solid to a gaseous state.
Another possible phenomenon is hail, which is rain formed by ice cubes.
know more about hail and snow.
Return of water to the surface
The water that falls from the sky in the form of rain or snow returns to the continents or water reservoirs from which it evaporated (lakes, rivers and oceans). Most of the precipitation (78%) occurs over the oceans.
The portion of water that falls on the continents can run over the terrain to lower areas, flowing towards rivers (runoff), or penetrate the soil (infiltration).
These large underground water deposits formed by the infiltration process are called aquifers. Aquifers also release water, either feeding rivers and lakes or forming springs. This process is known as aquifer discharge.
know more about aquifer.
Cycle restart
The water cycle is infinite. After water falls over continents or oceans, the cycle starts again with the evaporation described in the first step.
Importance of the Earth's water cycle
The water cycle is fundamental to the maintenance of life on Earth. Firstly, the water cycle is important because it distributes water across different regions of the planet. Now, without the water cycle, there would be no rainfall, which is essential for plantations, for air quality and for the replenishment of reservoirs, for example.
All of this has to do with a fundamental aspect of the water cycle: recycling. Water is a finite resource. All the water we use was here for many years before our existence. That same water will remain here on Earth long afterward. Whether the water used in farming or the water we drink, it will return to the water cycle and be recycled by nature.
Human interference in the water cycle
However, some human activities can disrupt the water cycle. One of the biggest threats to the proper functioning of this process is deforestation.
Perspiration from leaves is responsible for much of the moisture in the atmosphere. This moisture produces rain clouds. It is often said that forests like the Amazon, due to their enormous capacity for transpiration, produce “flying rivers”. These “flying rivers” (huge masses of air filled with water vapor) are responsible for the rain cycle in certain regions. In the case of Brazil, the rain cycle in the Midwest, Southeast and even the South of Brazil depends on the preservation of the Amazon Forest.
know more about Amazon rainforest and logging.
The water cycle and other biogeochemical cycles
Biogeochemical cycles are natural processes that promote the recycling of chemical elements, taking them from the environment to living organisms and then from living organisms to the environment. Through these cycles, the renewal of these elements takes place.
The water cycle is just one of the possible biogeochemical cycles. Chemical elements such as carbon, sulfur, oxygen and nitrogen also undergo continuous cycles of renewal. An example of this is carbon. In the carbon cycle, one of the most important steps is photosynthesis, through which beings such as plants remove carbon dioxide from the atmosphere and release oxygen.
See how the carbon cycle and know the meaning of photosynthesis and oxygen.
Check out other meanings:
- Types of natural resources
- greenhouse effect and global warming
- meaning of global warming
