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The Hydrologic (Water) Cycle

Posted Jun. 30, 1998

Three-fourths of the earth's surface is covered with water in the form of oceans, lakes and streams. Three percent is fresh of which 0.003 percent is in living organisms (plants and animals) and the soil, 0.6 percent is in underground aquifers, and the remainder is in ice. Those with a basic understanding of the water cycle and how it functions should be a step ahead during the current drought. However, "Mother Nature" is complex and often leaves those with the best of knowledge scrambling.

Evaporation: Water evaporates from lakes, ponds, rivers and streams, soil, plants, animals and people. Factories and machines, such as vehicles also evaporate water. Evaporated water moves into the atmosphere. Water also evaporates into the atmosphere as it falls in the form of precipitation.

Transpiration: Soil and surface water used by plants and animals and returned into the atmosphere.

Atmospheric water: Vapor from evaporation and transpiration which condenses and forms clouds.

Precipitation: Rain, sleet, snow, or hail falling from clouds (condensed atmospheric water).

Vegetation: Plants on the soil surface play a vital role in intercepting rain and slowing down runoff. Good soil cover by deep-rooted plants is a must in order to increase water availability.

Infiltration: Water entering the soil. Vegetation is the key to obtaining maximum infiltration rates on a particular soil type or range site.

Percolation or Gravitational flow: Water seeping through the soil profile into underground reservoirs.

The total amount of water on the earth is finite and in a closed system. In other words, no "new" water is made, nor is any lost. We face two problems with our earth's water cycle:

Pollution and Distribution

Pollution can be in the form of ground or air contamination.

Distribution can be a problem due to location, time, volume or all three. As mentioned before, the earth's water cycle is a closed system. However, the water cycle on your ranch or in your county is open. In other words, the amount of water your ranch or county receives in a given year is not constant.

The amount of water received in a given area depends on climate and geology. If we want more rain, we can move to an area that typically receives high rainfall. However, regardless of where we live, proper soil and vegetation management will maximize water quantity and quality when we need it.