 You'll find the hydrological cycle hard at work high in our atmosphere as well as several kilometers below the earth's surface. The cycle operates through a number of natural processes scientists call evaporation, transpiration and precipitation.
Evaporation describes the change from water as a liquid to water as a vapor. Water evaporated from ocean surfaces combines with water evaporated from freshwater sources such as rivers, lakes and streams to produce clouds.
The clouds, in turn, produce precipitation, 78 percent of which falls back into oceans while the remaining 22 percent falls back on land.
Transpiration, on the other hand, is the loss of water by plants. Transpiration rates depend upon temperature, humidity and wind speed conditions near the leaves of plants. And since plants draw water from the soil, transpiration rates can greatly effect soil moisture content. Soil water loss resulting from both transpiration and evaporation is called evapotranspiration.
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