Hydrologic Cycle Notes

Introduction The total amount of water on Earth never changes. There is the same amount of water now as there was millions of years ago. There will be the same amount of water millions of years from now too.

What is the water cycle? Water is always cycling through the atmosphere, ocean, and land. This process is called the hydrologic cycle (more commonly referred to as the water cycle). It is driven by energy from the sun. The water cycle is crucial to the existence of life on our planet.

1. Evaporation Evaporation is the process by which water changes from a liquid to a gas or vapor. Evaporation is the primary pathway that water moves from the liquid state back into the water cycle as atmospheric water vapor. Studies have shown that evaporation from the oceans, seas, lakes, and rivers provide nearly 90% of the moisture in the atmosphere.

Examples of Evaporation in our Everyday Lives

2. Condensation Condensation is the process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds. Condensation is the opposite of evaporation.

Examples of Condensation in our Everyday Lives

3. Precipitation Precipitation is water released from clouds in the form of rain, sleet, snow, or hail. Precipitation occurs when water droplets suspended in the sky become too big and fall to Earth. Most precipitation falls as rain.

4. Runoff/Collection Runoff is water that runs over the Earth’s surface. When rain hits saturated (soaked) ground, it begins to flow downhill. It is easy to see if it flows down your driveway to the curb and into a storm sewer, but it is harder to notice it flowing overland in a natural setting. During a heavy rain, you might notice water flowing downhill. Water will flow along channels as it moves into larger creeks, streams, and rivers. Eventually, runoff will reach the ocean.

5. Infiltration/Percolation Infiltration/Percolation is when water enters and filters through the ground. Anywhere in the world, a portion of the water that falls as rain and snow infiltrates into soil and rock. Some water that infiltrates will remain in the shallow soil layer, where it will gradually move through the soil. Eventually, it might enter a stream. Some of the water may infiltrate deeper into groundwater aquifers.

6. Groundwater Ground water is large amounts of water stored in the ground. The water is still moving, possibly very slowly. It is still part of the water cycle. Most of the water in the ground comes from precipitation that infiltrates downward from the Earth’s surface. Another term for ground water is "aquifer." Aquifers are huge storehouses of Earth's water. People all over the world depend on ground water in their daily lives.

7. Transpiration Transpiration is the evaporation of water from plant leaves. Studies have revealed that transpiration accounts for about 10% of the the moisture in the atmosphere.