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May 17, 2023 · What is the Water Cycle. Water cycle, also known as the hydrologic cycle, involves a series of stages that show the continuous movement and interchange of water between its three phases – solid, liquid, and gas, in the earth’s atmosphere.
The water cycle is a global cycle. It takes place on, above, and below Earth’s surface, as shown in Figure below. Like other biogeochemical cycles, there is no beginning or end to the water cycle. It just keeps repeating. During the water cycle, water occurs in three different states: gas (water vapor), liquid (water), and solid (ice). Many ...
- Overview
- Key points
- Water: Why does it matter?
- The water cycle
- The water cycle drives other cycles.
Learn how water moves through Earth's ecosystems.
•The vast majority of Earth's water is saltwater found in oceans. Only a tiny fraction is readily accessible freshwater, which is what humans need.
•Water found at the Earth's surface can cycle rapidly, but much of Earth's water lies in ice, oceans, and underground reservoirs; this water cycles slowly.
•The water cycle is complex and involves state changes in water as well as the physical movement of water through and between ecosystems.
•Groundwater is found underground between soil particles and in cracks of rocks. Aquifers are groundwater reservoirs often tapped by wells.
Water is pretty darn important for living things. Your body is more than one-half water, and if we were to take a look at your cells, we’d find they were over 70% water! So, you—like most land animals—need a reliable supply of fresh water to survive.
Of the water on Earth, 97.5% is salt water. Of the remaining water, over 99% is in the form of underground water or ice. All told, less than 1% of fresh water is found in lakes, rivers, and other available surface forms.
Many living things depend on this small supply of surface fresh water, and lack of water can have serious effects on ecosystems. Humans, of course, have come up with some technologies to increase water availability. These include digging wells to get at groundwater, collecting rainwater, and using desalination—salt removal—to get fresh water from the ocean. Still, clean, safe drinking water is not always available in many parts of the world today.
Most of the water on Earth does not cycle—move from one place to another—very rapidly. We can see this in the figure below, which shows the average time that an individual water molecule spends in each of Earth’s major water reservoirs, a measurement called residence time. Water in oceans, underground, and in the form of ice tends to cycle very slowly. Only surface water cycles rapidly.
The water cycle, or hydrologic cycle, is driven by the Sun’s energy. The sun warms the ocean surface and other surface water, causing liquid water to evaporate and ice to sublime—turn directly from a solid to a gas. These sun-driven processes move water into the atmosphere in the form of water vapor.
Over time, water vapor in the atmosphere condenses into clouds and eventually falls as precipitation, rain or snow. When precipitation reaches Earth's surface, it has a few options: it may evaporate again, flow over the surface, infiltrate into the soil, or percolate—sink down—into the ground.
In land-based, or terrestrial, ecosystems in their natural state, rain usually hits the leaves and other surfaces of plants before it reaches the soil. Some water evaporates quickly from the surfaces of the plants. The water that's left reaches the soil and, in most cases, will begin to move down into it.
In general, water moves along the surface as runoff only when the soil is saturated with water, when rain is falling very hard, or when the surface can't absorb much water. A non-absorbent surface could be rock in a natural ecosystem or asphalt or cement in an urban or suburban ecosystem.
Water in the upper levels of the soil can be taken up by plant roots. Plants use some of the water for their own metabolism, and water that's in plant tissues can find its way into animals’ bodies when the plants get eaten. However, most of the water that enters a plant's body will be lost back to the atmosphere in a process called transpiration. In transpiration, water enters through the roots, travels upwards through vascular tubes made out of dead cells, and evaporates through pores called stomata found in the leaves.
[Why would a plant take up water it's not going to use?]
The water cycle is important in itself, and patterns of water cycling and rainfall have major effects on Earth's ecosystems. However, rainfall and surface runoff also play important roles in the cycling of various elements. These include carbon, nitrogen, phosphorus, and sulfur. In particular, surface runoff helps move elements from terrestrial, land-based, to aquatic ecosystems.
We'll take a closer look at how this works in the following articles, where we'll examine different elements' biogeochemical cycles.
The water cycle, also known as the hydrological cycle, is a natural process that recycles water across the planet. It’s a continuous process that involves the evaporation of water from the Earth’s surface, its transport through the atmosphere, and its return to the surface through precipitation.
Course: How we interact with our environment - Class 12 > Unit 2. Lesson 3: Nutrient cycling. Biogeochemical cycles overview. The carbon cycle. The carbon cycle. The water cycle. The water cycle. The nitrogen cycle. The nitrogen cycle.
People also ask
What is the water cycle?
What is water cycle & why is it important?
What is the primary source of water for the water cycle?
Jun 2, 2009 · The answer is that water is constantly recycled through the Earth’s system through a process called the water cycle. The water cycle encompasses a number of processes that circulate water through the Earth’s subsystems.
