The Water Cycle Explained
Earth's water is constantly recycling through the hydrological cycle. The water you drink may have been drunk by dinosaurs.
The Stages
#### 1. Evaporation
Heat from the Sun causes water to evaporate from oceans, lakes, and rivers. Water molecules escape into the atmosphere as vapor.
Transpiration: Plants also release water vapor through their leaves.
#### 2. Condensation
As water vapor rises, it cools. Cool air holds less moisture. Water vapor condenses onto tiny particles (dust, pollen) forming clouds.
#### 3. Precipitation
When water droplets grow large enough, gravity pulls them down as rain, snow, sleet, or hail.
Orographic precipitation: Moist air rises over mountains, cools, and dumps precipitation on the windward side.
- Oceans: 97% of Earth's water
- Glaciers and ice caps: 2%
- Groundwater: Seeps into soil and rock
- Lakes, rivers, streams: Surface water
#### 5. Runoff
Water flows downhill, eventually reaching oceans. This transports nutrients, sediments, and pollutants.
Groundwater
Some precipitation infiltrates soil, filling underground aquifers. This groundwater can remain underground for thousands of years before emerging in springs or being pumped for human use.
The Role of the Sun
The Sun drives the entire cycle. Solar energy evaporates water and powers atmospheric circulation that moves moisture around the globe.
Human Impacts
- Climate change: Intensifying the cycle (more evaporation, heavier precipitation)
- Deforestation: Reducing transpiration
- Urbanization: Increasing runoff, reducing infiltration
Related Reading
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