Water Cycle!
What is the `Water Cycle` or `Hydrologic Cycle`?
Almost 93% water stored on the earth's surface is locked in the oceans which is toxic to humans and many plants and animals. How do we obtain fresh water resources then? Where does drinkable water come from? To understand, we need to turn to the Hydrologic Cycle.
The water cycle, also known as the hydrologic cycle, refers to the continuous movement of water between the earth and the atmosphere. Water reaches land as precipitation such as rain and snow. Then the water evaporates, condenses in the atmosphere to form clouds, and falls to the earth again as precipitation, continuing the cycle.
When water falls to the ground it can collect on the land becoming streams, rivers, lakes, or soaks in to the ground to become groundwater. Plants take up groundwater either using it or releasing it to the atmosphere.
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There are many components to the water cycle. They include:
- Evaporation is the process by which a substance changes from the liquid phase to the gas phase. It is the change of state of water (a liquid) to water vapor (a gas).
- Transpiration is evaporation of liquid water from plants and trees into the atmosphere. About 90% of all water that enters the roots transpires into the atmosphere.
- Sublimation is the process where ice and snow (a solid) changes into water vapor (a gas) without moving through the liquid phase.
- Condensation is the process by which a substance changes from the gas phase to the liquid phase. At this stage water vapor (a gas) changes back into a water droplets (a liquid). This is when we begin to see clouds, fog, dew, or frost form.
- Transportation is the movement of solid, liquid and gaseous water through the atmosphere. Without this movement, the water evaporated over the ocean would not precipitate over land.
- Precipitation is water that falls to the earth. Clouds are composed of millions of water droplets that have condensed. These water droplets grow into larger droplets by colliding and coalescing with one another. Eventually, the droplets can grow large enough that they will not be able to stay suspended in the cloud. When this occurs, they fall out of the cloud as precipitation. Most precipitation falls as rain but includes snow, sleet, drizzle, and hail.
- Runoff is the variety of ways of which water moves over the earth's surface. If precipitation occurs faster than it can infiltrate the ground, it becomes runoff. Runoff remains on the surface and flows into streams, rivers, and eventually large bodies such as lakes or the ocean.
- Infiltration is the movement of water into the ground from the surface. When precipitation falls to the surface, it will either be absorbed into the ground (groundwater) or, if the ground cannot absorb any more water, flow into streams.
- Groundwater flow is the flow of water underground in aquifers. The water may return to the surface in springs or eventually seep into the oceans.
- Plant uptake is water taken from the groundwater flow and soil moisture.
Why is the Hydrologic Cycle Important?
The hydrologic cycle is important because it is how water reaches plants, animals and us! It continues to move water and keep sources fresh. It is estimated that 100 million billion gallons a year are cycled through this process. Without this process life on Earth would be impossible. We need it to sustain us and for all of our life processes to function. Without water, life would not be possible on Earth.
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