The other name for the water cycle is the hydrologic cycle. It is a constant water circulation cycle in the Earth-atmosphere system. The essential processes of this cycle are condensation, evaporation, transpiration, precipitation, and runoff.
Fig.1 – The water cycle
Although the water’s overall quantity in this cycle remains largely constant, the distribution of that water among the different processes changes constantly.
Evaporation is one of the most important processes in this cycle because it transports water from the surface of the Earth to the atmosphere. Evaporation converts water from a liquid state to a gaseous (or vapor) state.
Fig.2 – Evaporation of ocean water
When certain molecules in a water mass gain enough kinetic energy to expel themselves off the water surface, this transfer happens.
Temperature, wind speed, humidity, and solar radiation are the primary variables that influence evaporation. Direct evaporation measurement is challenging and limited to point locations.
The seas are the primary source of water vapor, although evaporation also occurs in soils, snow, and ice. Sublimation is the direct conversion of a solid to vapor from the evaporation of snow and ice.
The water evaporation via minute holes, or stomata, is called transpiration. Transpiration and evaporation from the soil, water, snow, plants, ice, etc., are grouped and referred to as total evaporation or evapotranspiration.
Fig.3 – Transpiration by stomata in leaves of plants
Water vapor is highly essential in generating the moisture supply for dew, frost, fog, clouds, and precipitation, despite its tiny storage in the atmosphere. Almost the majority of the water vapor in the atmosphere is contained in the troposphere.
Condensation is transforming from a gaseous to a liquid state. When the air has more water vapor than it can acquire from a free water surface by evaporation at the current temperature, condensation may occur. This situation develops as a result of the mixing of air masses or cooling of various temperatures. Water vapor in the atmosphere is released as precipitation by condensation.
Precipitation that falls to the Earth is dispersed in four ways: some part evaporates back into the atmosphere, some are absorbed by plants and evaporated off the surface of leaves, some percolates into the soil via infiltration, and the rest runs directly into the sea as surface runoff. As groundwater runoff, some of the absorbed precipitation may eventually seep into streams.
The majority of groundwater comes from rainfall that has percolated through the Earth. When compared to surface water, groundwater flow rates are sluggish and variable, ranging from a few millimeters to a few meters per day. Tracer methods and remote sensing are used to study groundwater flow.
Ice plays an important role in the water cycle. Sea ice, frost, and glacier ice are all examples of snow and ice on the Earth's surface. In arctic regions, when soil moisture freezes, ice forms under the Earth's surface, creating permafrost.
WITHOUT FRESHWATER, WE WILL DIE - Humans can survive a maximum of one week without water, which makes up 60 to 70% of all living matter. Life on the planet would become increasingly difficult if this cycle was not maintained.
THE BIOGEOCHEMICAL CYCLE IS DRIVEN BY THE WATER CYCLE - A biogeochemical cycle which is also known as substance cycling or substance turnover, is a process through which a chemical substance travels through the biosphere (biotic) and atmosphere, lithosphere, and hydrosphere, which are abiotic compartments. Calcium, mercury, carbon, nitrogen, phosphorus, oxygen, sulfur, and selenium, as well as water and silica molecular cycles, are among them. Surface runoff, in particular, aids the transfer of components from terrestrial to aquatic environments.
DISTRIBUTION - Perhaps most importantly, the water cycle equitably distributes water throughout the surface of the Earth. This is significant because if water were not dispersed, gravity would force it all to the lowest point on the planet, the seas. The water cycle provides freshwater to all living creatures on the Earth, including people, animals, and plants. Runoff feeds rivers, other bodies of fresh water, and ultimately the ocean, maintaining both freshwater and marine life.
PURIFICATION - By cleaning water, evaporation enhances human, animal, and plant life. Pollutants and sediments are left behind when water evaporates. The ground cleanses water as it infiltrates, removing impurities and toxins. Glaciers, ice, and snow can serve as freshwater reservoirs for people and other animals. Because saltwater must be within particular pH and saline limits, even aquatic life needs clean water.