Water Resource Management
The Hydrologic Cycle
Water is the source of all life on earth. The distribution of water, however, is quite varied;
many locations have plenty of it while others have very little. Water exists on earth as a
solid (ice), liquid or gas (water vapor). Oceans, rivers, clouds, and rain, all of which
contain water, are in a frequent state of change (surface after evaporates, cloud water
precipitates, rainfall infiltrates the ground, etc.). However, the total amount of the earth
water does not change. The circulation and conservation of earth water is called the
*ƒ²*ƒ”€š?hydrologic cycle”“.
Introduction
The hydrologic cycle begins with the evaporation of water from the surface of the ocean.
As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is
transported around the globe until it returns to the surface as precipitation. Once the water
reaches the ground, one of two processes may occur; 1) some of the water may evaporate
back into the atmosphere or 2) the water may penetrate the surface and become
groundwater. Groundwater either seeps its way to into the oceans, rivers, and streams, or is
released back into the atmosphere through transpiration. The balance of water that remains
on the earth surface is runoff, which empties into lakes, rivers and streams and is carried
back to the oceans, where the cycle begins again.
Lake effect snowfall is good example of the hydrologic cycle at work. Below is a vertical
cross-section summarizing the processes of the hydrologic cycle that contribute to the
production of lake effect snow? The cycle begins as cold winds (horizontal blue arrows)
blow across a large lake, a phenomenon that occurs frequently in the late fall and winter
months around the Great Lakes.
Evaporation of warm surface water increases the amount of moisture in the colder, drier air
flowing immediately above the lake surface. With continued evaporation, water vapor in
the cold air condenses to form ice-crystal clouds, which are transported toward shore.
By the time these clouds reach the shoreline, they are filled with snowflakes too large to
remain suspended in the air and consequently, they fall along the shoreline as precipitation.
The intensity of lake effect snowfall can be enhanced by additional lifting due to the
topographical features (hills) along the shoreline. Once the snow begins to melt, the water
is either absorbed by the ground and becomes groundwater, or goes returns back to the
lake as runoff.
Earth Water Budget
Water covers 70% of the earth surface, but it is difficult to comprehend the total amount of
