What is Water Cycle?
The hydrologic cycle is another name for the water cycle. It is a cycle in which water flows constantly in the Earth-atmosphere system. The most crucial processes present in the water cycle are evaporation, transpiration, condensation, precipitation, and runoff. While the total amount of water in the cycle remains relatively constant, how that water is distributed across the various processes changes over time.
This is the brief explanation of what is water cycle. There are different water cycle models, where students can try it to understand the real time working.
Process of Water Cycle
The process of water cycle is a very interesting concept to discuss. Let us take a look at it.
The transformation of water from the surface of Earth to the atmosphere is referred to as evaporation, and it is one of the most critical water cycle steps. The liquid state of water is transformed to either the gaseous, or vapour, state by the evaporation process. When some molecules in a water mass gain sufficient kinetic energy to dislodge themselves off the water surface, this transfer occurs. Temperature, humidity, wind speed, and sun radiation are the key factors that influence evaporation.
Direct evaporation measurement, while desirable, is difficult and restricted to point locations. The oceans are the primary source of water vapour, but evaporation also occurs in soils, snow, and ice. Sublimation is defined as the direct conversion of a solid to a vapour from evaporation of snow and ice. Whereas, transpiration is defined as the process of water evaporating from a plant's leaves through minute pores called stomata. Transpiration and evaporation from all water, soils, snow, ice, vegetation, and other surfaces are grouped together and referred to as evapotranspiration, or total evaporation, for practical purposes.
Water vapour is the most common type of moisture in the air. Water vapour is particularly vital in producing the moisture supply for dew, frost, fog, clouds, and precipitation, despite its modest storage in the atmosphere. The troposphere is composed of almost all of the water vapour in the atmosphere (the region lies 6 - 8 miles (10 to 13 km) altitude).
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Condensation is the transformation of a gaseous state to a liquid state. When the air has more water vapour than it can obtain from a free water surface by evaporation at the current temperature, condensation may occur. This state happens as a result of cooling or the mixing of air masses of various temperatures. Water vapour in the atmosphere is released as precipitation by condensation.
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Fog develops along the coast of King Range National Conservation Area in Humboldt County, California, when water vapour condenses on condensation nuclei that are constantly present in natural air.
Precipitation is the process that falls to the surface of the Earth, is distributed in four ways: part evaporates back into the atmosphere, some is collected by vegetation and evaporated from the surface of leaves, some percolates into the soil via infiltration, and the rest flows directly into the sea as surface runoff. As groundwater runoff, some of the infiltrated precipitation may eventually seep into streams. Stream gauges are used to measure runoff directly and plot it against time on hydrographs.
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Major part of Indonesia receives abundant rainfall throughout the year.
The majority of groundwater is derived from the cycle of rainfall that has leaked into the ground. When compared to surface water, groundwater flow rates are slow and varied, ranging from a few millimetres to a few metres per day. Groundwater movement is investigated using tracer techniques and remote sensing.
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In the water cycle, ice also plays a role. Frost, sea ice, and glacier ice are all examples of ice and snow on the Earth's surface. In tundra climates, when soil moisture freezes, ice forms beneath the Earth's surface, generating permafrost. Glaciers and ice caps covered roughly one-third of the Earth's land surface about 18,000 years ago. Approximately 12% of the land surface is still covered by ice masses today. There are different water cycle models available.
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Argentina's Perito Moreno glacier is one of the many parts of Patagonia, which are cold enough to be covered by the ice layers.
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Stages of Water Cycle
The stages of water cycle is divided into four parts. Evaporation, condensation, precipitation, and collecting are the four stages of water cycle. Let us understand each of these water cycle steps one by one.
Evaporation: When the sun's warmth causes water from oceans, lakes, streams, ice, and soils to rise into the air and transform into water vapour, this is known as evaporation (gas). Clouds are formed when water vapour droplets come together.
Condensation: This is when atmospheric water vapour cools and condenses back into liquid water.
Precipitation: This occurs when water (in the form of cycle of rain, snow, hail, or sleet) falls from the sky in various forms such as snow, rain, hail, or sleet.
Collection: When a cycle of rain, snow, hail, or sleet falls from the sky and settles in the oceans, rivers, lakes, and streams, this is known as a storm. The majority of the water will sink into the ground and collect as groundwater.
Gravity and the sun's energies drive the water cycle. The cycle starts with the sun heating and evaporating all of the Earth's water. The moisture falls back to Earth due to gravity.
Importance of Water Cycle
Let us discuss the importance of water cycle here.
The water cycle is highly important because it ensures that all the living organisms will be given access to the water and regulates weather patterns on Earth (our planet). If water would not naturally recycle itself, we would run out of clean water, which is essential for life.
Freshwater appears abundant, but it is in short supply when compared to the total amount of water on the Earth (our planet). Freshwater makes up just 3% of the water on our planet. The majority of this water, approximately 2% of total global water, is held in glaciers and ice sheets or underground. The remaining 1% is found in lakes, rivers, and wetlands, or is carried through the atmosphere as water vapour, clouds, and precipitation.
Rain and snow replenish freshwater supplies, thus knowing when, where, and how much water is falling at any particular time is critical. Any of the researchers can track the precipitation globally and monitor levels from space using NASA's Global Precipitation Measurement satellite.
Summary on Water Cycle
Where does all of the water on the earth come from? The primordial Earth was a glowing magma globe, yet all magmas contain water. The water produced by magma began to temper the Earth's atmosphere, enabling it to remain liquid on the surface. Volcanic activity has kept and continues to introduce water into the atmosphere, increasing the Earth's surface and groundwater volume.
At any point of time, there will be no start and finish to the water cycle. But, because the seas contain the majority of the Earth's water, we'll start there. The sun will heats the water, taking from the oceans, which drives the water cycle. Some of it evaporates into the atmosphere as vapour. Ice and snow can directly sublimate into water vapour. Rising air currents carry the vapour, as well as water from evapotranspiration (water transpired by plants and evaporated from the soil), into the atmosphere. The vapour rises into the air, where it condenses form clouds due to cooler temperatures.
FAQs on Water Cycle
1. What is the water cycle, and why is it also called the hydrologic cycle?
The water cycle is the continuous movement of water on, above, and below the surface of the Earth. It's a closed system, meaning the total amount of water remains constant. It is also known as the hydrologic cycle because 'hydro' means water in Greek, and the term describes the science of water's movement and distribution.
2. What are the four main stages of the water cycle as per the NCERT syllabus?
The four main stages of the water cycle, crucial for understanding its process as per the 2025-26 CBSE curriculum, are:
- Evaporation: The process where the sun's heat turns liquid water from oceans, lakes, and rivers into a gas called water vapour, which then rises into the atmosphere.
- Condensation: As the water vapour rises, it cools and changes back into tiny liquid water droplets, forming clouds.
- Precipitation: When the water droplets in clouds become too heavy, they fall back to Earth as rain, snow, sleet, or hail.
- Collection: The fallen precipitation is collected in bodies of water like oceans, rivers, and lakes, or it soaks into the ground as groundwater, starting the cycle again.
3. What is the role of the Sun in driving the water cycle?
The Sun acts as the primary engine of the water cycle. Its energy is essential for the first stage, evaporation. The sun's heat provides the necessary kinetic energy for water molecules to escape from the surface of oceans, lakes, and rivers and transform into water vapour. Without the sun's energy, water would not evaporate to begin its journey into the atmosphere, and the entire cycle would stop.
4. What is the difference between evaporation and transpiration in the water cycle?
Both evaporation and transpiration release water vapour into the atmosphere, but they differ in their source. Evaporation is the process of water turning into vapour from open water surfaces like oceans, rivers, and soil. In contrast, transpiration is the process where plants absorb water through their roots and then release it as water vapour from small pores in their leaves called stomata. The combined process is often called evapotranspiration.
5. What happens to the water after precipitation? Does it all flow back to the oceans?
No, not all water returns directly to the oceans after precipitation. It follows several paths:
- Surface Runoff: Some water flows over the land's surface, gathering in streams, rivers, and eventually making its way to lakes and oceans.
- Infiltration: A significant portion soaks into the ground, a process called infiltration. This water becomes groundwater, which can be stored underground for long periods.
- Collection: It can also be collected in lakes, glaciers, and ice caps, where it may be stored for years before continuing the cycle.
6. Are there more than four stages in the water cycle? For example, what about runoff and infiltration?
While evaporation, condensation, precipitation, and collection are considered the four main stages, the water cycle is more complex. Processes like runoff and infiltration are not separate stages but are crucial parts of the cycle. Runoff is a key component of the collection phase, describing how water moves over land to gather in rivers and lakes. Similarly, infiltration is another part of collection, explaining how water seeps into the ground to replenish groundwater reserves. They describe the detailed pathways water takes between the main stages.
7. Besides providing us with rain, what is the importance of the water cycle for the planet?
The importance of the water cycle extends far beyond just providing rain. It plays a critical role in:
- Regulating Earth's Climate: By moving water and heat around the globe, the cycle helps moderate temperatures, making different regions of the planet habitable.
- Purifying Water: The process of evaporation naturally purifies water. As water evaporates, it leaves behind salts, minerals, and impurities, ensuring a supply of fresh water through precipitation.
- Sustaining Ecosystems: It transports nutrients and minerals essential for life in both aquatic and terrestrial ecosystems.
8. If water on Earth is in a continuous cycle, where did our planet's water originally come from?
This is a topic of scientific study with two primary theories. The first theory suggests that when Earth was a young, molten planet, water was trapped inside magma. Through intense volcanic activity (outgassing), this water was released into the atmosphere as steam, which later condensed to form oceans. A second theory proposes that a significant amount of Earth's water was delivered by ice-rich asteroids and comets that collided with our planet billions of years ago.
