Re: what is the hydrologic cycle?

MadSci Network: Agricultural Sciences

Re: what is the hydrologic cycle?

Date: Mon May 11 14:04:04 1998
Posted By: R. Ted Jeo, Bio Sci Tech, St. Paul, MN
Area of science: Agricultural Sciences
ID: 894383804.Ag

Message:

The Hydrologic Cycle

As you may realize, the hydrologic cycle has to do with the cycle of water on this planet. As it is a cycle, water is not lost completely, it just changes forms and location. Most of the Earth's water is located in the oceans (nearly 98%). The ice caps and glaciers hold about 2%, ground and soil water account for around a half percent, rivers and lakes account for about 0.02% and the atmosphere holds a tiny amount. All this water is not necessarily moving all the time, nor is it completely locked up forever in one location. It migrates (moves) around and changes form (vapor, liquid, ice). The hydrologic cycle encompasses the movement of water from the air, oceans, land, underground and ice caps. Let's take a look and describe the major parts of the cycle.

The hydrologic cycle really does not have a starting point, so we will start with ocean water where most of the water is located:

Ocean water is drawn up into the atmosphere via evaporation.

Evaporation leads to either storage of some water vapor in the atmosphere or it leads to precipitation.

Precipitation can take place in the form of rain, snow or ice.

Some of the precipitation will fall back into the ocean.

Some of the precipitation never reaches the ground, instead it evaporates again and stays in the atmosphere.

Some precipitation can accumulate into the ice caps and glaciers and may be immobilized for a long time, but it may melt and become surface run off or it can evaporate directly back to the atmosphere (called sublimation).

Some precipitation falls to the ground and runs off into streams, rivers, lakes and may just flow back to the ocean.

Some precipitation will soak through the soil and seep farther below to become ground water.

Ground water may be immobilized for a time, but it may flow or be pumped back to the surface where it can become surface runoff or evaporate to the atmosphere.

Some precipitation will fall on the ground and evaporate back to the atmosphere.

Some precipitation will soak into the soil and become soil water for plants to use.

Plants will draw up water from the surface, soil or deeper and will release it back to the atmosphere via transpiration.

So, as you can see, there is no real 'starting point'. You can take any step above and trace where the water goes, and it might just return back where it started. Click here for a diagram and discussion about the hydrologic cycle for a Physical Geography class at Okanagan University in British Columbia, Canada.

Hope this answers your question.
Ted

Current Queue | Current Queue for Agricultural Sciences | Agricultural Sciences archives

Try the links in the MadSci Library for more information on Agricultural Sciences.