The Water Cycle Or The Hydrologic Cycle
Arguably the most important natural phenomenon on Earth, the water cycle, also known as the hydrologic cycle, describes the constant movement and endless recycling of water between the atmosphere, land surface, and under the ground. The hydrologic cycle supplies the force needed for most natural processes, thus supporting life itself.
The Water Molecule • H20 consists of one atom of oxygen bound to two atoms of hydrogen. The water molecule has a positive charge on the side of hydrogen atoms and a negative charge on the other side. Water molecules tend to attract each other because the positive ends attract to the negative ends.
Water is a “universal solvent: and wherever it goes throughout the water cycle, it takes up valuable chemicals, minerals and nutrients.
Condensation The change from water vapor (gas) to liquid. In the water cycle, the change is from water vapor to a form of precipitation.
Condensation & Convection • Warm air rises • Air cools and can no longer hold vapor • Process known as CONVECTION
Condensation & Cloud Formation • Cooling of water vapor forms CLOUDS • Other ways clouds are formed • Convergence • Lifting of air by fronts
Snow • Snow is a type of precipitation like rain but at cooler temperatures • Usually reaches the ground and stays • Eventually melts and becomes runoff in streams
Rain • Type of precipitation during warmer weather • Occurs when clouds become too full • Falls to earth in the form of water and runs off to streams & rivers
Freshwater Storage • Water may be stored temporarily in the ground, oceans, lakes, rivers, and in ice caps and glaciers.
The world’s two main reservoirs of fresh water are the great polar ice caps, and the ground. • If all of the ice in the ice caps and other glaciers melted, it would raise the sea level by about 260 ft.
In temperate climates, water is found in depression storage or surface water puddles, ditches, and anywhere else that runoff water can gather. This is a temporary form ofstorage
A hydrologist is particularly interested in stream flow -- the 31% of precipitation which runs off into rivers, streams and lakes.
About 3% of this water will seep underground • About 31% will run off into rivers, streams and lakes • About 66% of the water returns to the atmosphere through evaporation and transpiration
Surface Runoff • When precipitation rate exceeds infiltration rate, or when soil is saturated, water begins to move down slope on ground surface.
Surface Runoff • surface runoff gradually flows into gullies, streams, lakes, or rivers. Water in streams and rivers flows to the ocean, seeps into the ground, or evaporates back into the atmosphere.
The largest reservoir is the oceans. There is about 50 times as much water in the oceans than in the next largest reservoir, polar ice and glaciers.
Water Storage in Ice and Snow Water precipitates into cooler areas of land and freeze into ice and snow.
Snowmelt Runoff to Streams • Precipitation falls in the form of rain and snow • When the snow melts it runs into streams which eventually dump into the ocean
-Rain water soaks into ground through soil and underlying rock layer. -Water cleaned as impurities filtered
-Some water remains underground as groundwater. -Some water returns to surface at springs or low spots downhill.
- water seeps downward underground into soil and rock crevices -then stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust
-Water storage under the ground largely depends on the geologic features related to the types of soil and the types of rocks present at the storage locations. -underground storage occurs in the soil, in aquifers, and in the crevices of rock formations
Evaporation • Conversion of water from a liquid into a gas • Water transferred from surface to atmosphere through evaporation
Evaporation & the Sun The sun heats up water in the ocean, rivers, or lakes, turning it into vapor, which then goes into the air
Evaporation Cont. • 80% of evaporation from ocean • 20% of evaporation from inland water and vegetation • Winds transport evaporated water, influencing humidity around the world
Transpiration The process of evaporation from plants. Basically, plants sweating.
Transpiration Cont. Environmental factors that affect transpiration: • Light • Temperature • Humidity • Wind • Soil water
Good For Plants!! • Transpiration is the “engine” of plant life, pulling water up from the roots. This allows for photosynthesis, brings minerals from the roots to the rest of the plant, and cools the leaves.
Source % of Supply Oceans 97.08 Ice Sheets and Glaciers 1.99 Ground Water 0.62 Atmosphere 0.29 Lakes (Fresh) 0.01 Inland Seas / Salt Water Lakes 0.005 Soil Moisture 0.004 Rivers 0.001 -atmosphere holds only very small percentage of Earth’s water supply at any given time -rapid recycling of water must occur between earth's surface and atmosphere World Water Supply
- Water stored in the atmosphere can be moved relatively quickly from one part of the planet to another part of the planet