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Technical
Resources >> Water Sources
>> The Hydrologic Cycle
| Water, one of earths most precious
resources, exists in several forms in the environment including sea
water, sea-ice, fresh water, and water vapor as clouds and mist. As
it moves through the environment it picks up gasses and elements,
flows to the sea and through ground, in an endless process known as
the hydrologic cycle. |
| Studying the concept of the hydrologic
cycle is perhaps the most useful way to understand how precious fresh
water is, and how important the health of the oceans are to sustain
life on the planet. The term 'hydrologic cycle" refers to the
day-to-day and long term changes in the hydrosphere. The cycle may
be viewed as a description of the ways in which water moves around
the earth. It is important because it accounts for the circulation
of water in all the different states. Planners may use the hydrologic
cycle as a conceptual tool in order to anticipate problems and consequences
which may arise from development. Students typically study the hydrologic
cycle in high school. |
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| The distribution of water is the
key to understanding the hydrologic cycle as well as the availability
of water for human use or consumption. The current distribution is
as follows: |
| Percentage of Water Location/Form |
| 97.200% |
salt water in the oceans |
| 02.014% |
ice caps and glaciers |
| 00.600% |
groundwater |
| 00.009% |
surface water |
| 00.005% |
soil moisture |
| 00.001% |
atmospheric moisture |
| Of this distribution, the two sources
of available freshwater consist of groundwater and surface water.
Therefore, approximately 98% of the available freshwater is in the
form of groundwater while the remaining 2% is in the form of surface
water. |
| As seen in the schematic above, the hydrologic cycle
is the continuous circulation of water from the ocean to the atmosphere
to the earth and back to the ocean. This cycle is solar powered as
the water from the ocean and the land surface evaporates to the atmosphere.
Throughout the cycle, water may be temporarily stored in lakes, streams,
the soil, as groundwater, etc. |
| The amount of storage is calculated by
using the hydrologic equation. The goal of this equation is to maintain
mass balance of the water around the earth. Conceptually, this equation
considers the influx of water less the outflux in order to achieve
the change in storage. Examples of influxes are precipitation, streams,
overland flow, and groundwater. While some examples of outfluxes include
evaporation, groundwater, and streams. |
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