2.3 Hydrological Cycle

fig 2.3 (a)

This cycle of water movement from water bodies to the atmosphere and, through precipitation, to the land and back to the water bodies, is called the hydrologic cycle. It is also known as the water cycle. The hydrological cycle describes what happens to the estimated 8000 cubic miles of water that evaporates from the oceans and various water bodies each year.

          Nearly 90 per cent of this water is returned to the oceans by direct precipitation (rain, snow, hail, sleet). The remaining 10 per cent enter the atmosphere, condense and precipitate over land. From there it eventually migrates back to the sea by run-off or ground water movement or to the atmosphere by evaporation from open water or transpiration from plants.

Although the hydrologic cycle balances what goes up with what comes down, one phase of the cycle is "frozen" in the colder regions during the winter season. During the winter, for example, most of the precipitation is simply stored as snow or ice on the ground. Later, during the spring melt, huge quantities of water are released quickly, which results in heavy spring runoff and flooding.

 fig 2.3(b)