The hydrologic cycle involves the continuous circulation of water in the Earth-Atmosphere system. At its core, the water cycle is the motion of the water from the ground to the atmosphere and back again. Of the many processes involved in the hydrologic cycle, the most important are...
- This change of state of water occurs in the atmosphere and between the earth's surface and atmosphere.
- change of state or phase change = solid > liquid > gas
This basic cycle is seen almost daily around the world in the formation and dissipation of clouds. When a cloud develops it is water vapor becoming a liquid. Conversely, when a cloud dissipates, liquid water changes state back into a gas.
The Ocean's Role
The vast bulk of the water in the water cycle is found in the oceans. The oceans hold 96.5% of the earth's water and due to their size it may take thousands of years for a water molecule to move from the ocean to the atmosphere. This is in spite of an average 45 inches (114 cm) of water that evaporates from the ocean each year. (An additional 1% of salty water is also found in saltwater lakes and saline groundwater.)
The highest rate of evaporation from the oceans occurs in winter for both the Northern and Southern Hemispheres. The location of greatest evaporation is found on the east coasts of continents. (See maps lower right.) This is due primarily to winter storms that move off the east coasts of continents which tend to have strong winds. These winds help carry water vapor away from its source thereby allowing more evaporation to take place.
Maximum global evaporation rates.
The other factor is the warm ocean currents that move pole-ward along the east coasts of continents. The cold winter-time air masses that move over the water allow for large differences in air and sea temperatures so evaporation is also large. Then, when these differences in air and sea temperatures are combined with strong winds it makes evaporation in these regions very efficient.
Yet, of all evaporation that occurs over the oceans, a little over 90% of the moisture falls directly back into the sea as precipitation. And after spending upwards of a few thousand years in the ocean, a water molecule, on average, will only spend about nine days in the atmosphere before returning to earth. This is a very simple water cycle!
But over land, the water cycle can become quite complicated. The remaining 10% of moisture is transported over land and falls as precipitation from where it can travel a myriad of paths. If the precipitation falls as snow, it can remain frozen for a day or two then melt and flow into a river. Or the snow can become compacted and be locked up in a glacier for centuries.
Some water may infiltrate the soil or percolate into the groundwater. While most groundwater returns to the ocean, some groundwater can bubble up to the surface as a spring and evaporate back into the atmosphere, flow into a river, or even be captured and bottled for human consumption.
Yet, of all evaporation that occurs over the oceans, a little over 90% of the moisture falls directly back into the sea as precipitation. And after spending upwards of a few thousand years in the ocean, a water molecule, on average, will only spend about nine days in the atmosphere before returning to earth. This is a very simple water cycle!
But over land, the water cycle can become quite complicated. The remaining 10% of moisture is transported over land and falls as precipitation from where it can travel a myriad of paths. If the precipitation falls as snow, it can remain frozen for a day or two then melt and flow into a river. Or the snow can become compacted and be locked up in a glacier for centuries.
Some water may infiltrate the soil or percolate into the groundwater. While most groundwater returns to the ocean, some groundwater can bubble up to the surface as a spring and evaporate back into the atmosphere, flow into a river, or even be captured and bottled for human consumption.
But remember, of all the water on the earth only 2.5% is fresh water and nearly all of that fresh water is locked up in glaciers and groundwater. Perhaps surprisingly, the atmosphere only contains about one-thousandths percent of all water on the earth.
The distribution of fresh water as well as an estimation of the time a water molecule remains in various features, can be seen in the table (below).
The distribution of fresh water as well as an estimation of the time a water molecule remains in various features, can be seen in the table (below).
| Estimate of global FRESH water distribution | Total Water (%) | FRESH Water (%) | Duration |
|---|---|---|---|
| Ice caps, Glaciers, & Permanent Snow | 1.74 | 68.7 | > 1000 years |
| Groundwater | 0.76 | 30.1 | ~300 years |
| Soil Moisture | 0.001 | 0.05 | ~280 days |
| Ground Ice & Permafrost | 0.022 | 0.86 | |
| Lakes | 0.007 | 0.26 | 1-100 years |
| Atmosphere | 0.001 | 0.04 | 9-10 days |
| Wetlands | 0.0008 | 0.03 | |
| Rivers | 0.0002 | 0.006 | 12-20 days |
| Humans / Animals / Plants | 0.0001 | 0.003 |
- evaporation
- transpiration
- condensation
- precipitation
- runoff
Evaporation (CLICK)
Evaporation is the change of state in a substance from a liquid to a gas. In meteorology, the substance we are concerned about the most is water.
Evaporation is the change of state in a substance from a liquid to a gas. In meteorology, the substance we are concerned about the most is water.
For evaporation to take place, energy is required. The energy can come from any source: the sun, the atmosphere, the earth, or objects on the earth such as humans.
Everyone has experienced evaporation personally. When the body heats up due to the air temperature or through exercise, the body sweats, secreting water onto the skin.
The purpose is to cause the body to use its heat to evaporate the liquid, thereby removing heat and cooling the body. It is the same effect that can be seen when you step out of a shower or swimming pool. The coolness you feel is from the removing of bodily heat to evaporate the water on your skin.
Transpiration
Transpiration is the evaporation of water from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process of the plant. The remaining 99% is passed into the atmosphere.
Transpiration is the evaporation of water from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process of the plant. The remaining 99% is passed into the atmosphere.CONDENSATION
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Condensation is the process whereby water vapor in the atmosphere is changed into a liquid state. In the atmosphere condensation may appear as clouds or dew. Condensation is the process whereby water appears on the side of an uninsulated cold drink can or bottle.
Condensation is not a matter of one particular temperature but of a difference between two temperatures; the air temperature and the dewpoint temperature. At its basic meaning, the dewpoint is the temperature where dew can form. Actually, it is the temperature that, if the air is cool to that level, the air becomes saturated. Any additional cooling causes water vapor to condense. Foggy conditions often occur when air temperature and dewpoint are equal.
Condensation is the opposite of evaporation. Since water vapor has a higher energy level than that of liquid water, when condensation occurs, the excess energy in the form of heat energy is released. This release of heat aids in the formation of hurricanes.
Precipitation
Precipitation is the result when the tiny condensation particles grow too large, through collision and coalesce, for the rising air to support, and thus fall to the earth. Precipitation can be in the form of rain, hail, snow or sleet.
Precipitation is the primary way we receive fresh water in earth. On average, the world receives about 38½" (980 mm) each year over both the oceans and land masses.
Runoff
Runoff occurs when there is excessive precipitation and the ground is saturated (cannot absorb anymore water). Rivers and lakes are results of runoff. There is some evaporation from runoff into the atmosphere but for the most part water in rivers and lakes return to the oceans.
If runoff water flows into the lake only (with no outlet for water to flow out of the lake), then evaporation is the only means for water to return to the atmosphere. With evaporation only pure water evaporated, and therefore any contaminates and salts are left behind. The result is the lake becomes salty as in the case of the Great Salt Lake in Utah or Dead Sea in Israel.
Evaporation of this runoff into the atmosphere begins the hydrologic cycle over again. Some of the water percolates into the soil and into the ground water only to be drawn into plants again for transpiration to take place.
GROUND WATER POLLUTION CLEAN-UP
1. Evaporation is the change of state of water )a liquid) to water vapor (a gas). On average about 47 inches (120 cm) is evaporated into the atmosphere from the ocean each year.
2. Transpiration is evaporation of liquid water from plants and trees into the atmosphere. Nearly all (99%) of all water that enters the roots transpires into the atmosphere.
3. Sublimation is the process where ice and snow (a solid) changes into water vapor (a gas) without moving through the liquid phase.
4. Condensation is the process where water vapor (a gas) changes into water droplets
(a liquid). This is when we begin to see clouds
5. Transportation is the movement of solid, liquid and gaseous water through the atmosphere. Without this movement, the water evaporated over the ocean would not
precipitate over land.
6. Precipitation is water that falls to the earth. Most precipitation falls as rain but includes snow, sleet, drizzle, and hail. On average, about 39 inches (980 mm) of rain, snow and sleet fall each year around the world.
7. Deposition is the reverse of sublimation. Water vapor (a gas) changes into ice (a
solid) without going through the liquid phase. This is most often seen on clear, cold
nights when frost forms on the ground
8. Infiltration is the movement of water into the ground from the surface. Percolation is movement of water past the soil going deep into the groundwater.
9. Surface flow is the river, lake, and stream transport of water to the oceans.
Groundwater is the flow of water under- ground in aquifers. The water may return to the
surface in springs or eventually seep into the oceans.
10. Transpiration/Plant uptake is water taken from the groundwater flow and soil moisture. Only 1% of water the plant draws up is used by the plant. The remaining 99% is passed back into the atmosphere.
HYDROLOGIC CYCLE - QUIZ
- DO NOT USE NOTES
- write your quiz name, score & your name on notebook paper & turn into drawer
thanks to NASA http://www.srh.weather.gov/jetstream/atmos/hydro.htm
