Overview
This lecture explains the water cycle, describing how water continuously moves through various stages and locations on Earth, enabling life through its ongoing processes.
The Water Cycle Basics
- All water on Earth is ancient and continually recirculated in a looping process.
- The water cycle consists of two concepts: flows (movement of water) and stores (where water is held).
- Major water stores include oceans, ice sheets, glaciers, lakes, rivers, soil, plants, and underground aquifers.
- Water is always moving between these different stores in various forms.
Movement of Water (Flows)
- Precipitation is water falling to Earth as rain, snow, hail, or sleet.
- Fog and mist are forms of precipitation where water is in vapor form.
- Rain falling into oceans becomes part of surface water and can enter ocean currents.
- Snow and ice melting on mountaintops flow into rivers through tributaries.
- Precipitation intercepted by plants or trees does not reach the ground directly.
- Water that hits hard surfaces or saturated soil runs off into streams or rivers.
- Infiltration is when water seeps into the soil; percolation is the downward movement through soil layers.
- Groundwater flows through soil, rocks, and aquifers; deep groundwater moves very slowly.
Return to Atmosphere
- Evaporation is the transformation of water from liquid to gas via heat, occurring from all wet surfaces.
- Transpiration is water released from plant leaves into the air.
- Evapotranspiration combines evaporation from soil/water and transpiration from plants.
- Water vapor rises, condenses into clouds, and eventually falls again as precipitation.
Key Terms & Definitions
- Water Cycle — continuous movement of water through Earth's atmosphere, surface, and underground.
- Store — a location where water is held (e.g., oceans, lakes, aquifers).
- Flow — movement of water between stores.
- Precipitation — water falling to Earth's surface as rain, snow, sleet, or hail.
- Runoff — water flowing over the surface into rivers or lakes.
- Interception — precipitation captured by plants or trees before reaching the ground.
- Infiltration — process of water seeping into soil.
- Percolation — downward movement of water through soil and rock layers.
- Aquifer — underground layer of water-bearing rock.
- Evaporation — process of water changing from liquid to vapor.
- Transpiration — water released from plants into the atmosphere.
- Evapotranspiration — total water lost from evaporation and transpiration.
- Condensation — process where water vapor becomes liquid, forming clouds.
Action Items / Next Steps
- Review definitions of key water cycle processes.
- Diagram the water cycle, labeling each major store and flow.