Hydrologic Cycle/Water Balances

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Hydrologic Cycle/Water Balances
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Earths Water

• Covers approximately 75 of the surface
• Volcanic emissions
• Only known substance that naturally exists as a
  gas, liquid, and solid at surface temperatures
  and pressures

http//earthobservatory.nasa.gov/Library/Water/
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One estimate of global water distribution
http//earthobservatory.nasa.gov/Library/Water/
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Fresh Water
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Hydrologic Cycle

• Powered by energy from the sun
• Evaporation 90 of atmospheric water
• Transpiration 10
• Evaporation exceeds precipitation over oceans
• Precipitation exceeds evaporation over continents
• All water stored in atmosphere would cover
  surface to a depth of 2.5 centimeters
• 1 m average annual precipitation

http//earthobservatory.nasa.gov/Library/Water/
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Hydrologic Cycle
In the hydrologic cycle, individual water
molecules travel between the oceans, water vapor
in the atmosphere, water and ice on the land, and
underground water. (Image by Hailey King, NASA
GSFC.)
http//earthobservatory.nasa.gov/Library/Water/
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Florida
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Florida
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U.S. total, surface-water, and ground-water
withdrawals, 2000
http//water.usgs.gov/pubs/circ/ 2004/circ1268/htd
ocs/text-total.html
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U.S. total water withdrawals by category, 2000
http//water.usgs.gov/pubs/circ/2004/circ1268/htdo
cs/text-total.html
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Trends in population and freshwater withdrawals
by source, 1950-2000
http//water.usgs.gov/pubs/circ/2004/circ1268/htdo
cs/text-total.html
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Water (Mass) Balance

• In Out Change in Storage
• Totally general
• Usually for a particular time interval
• Many ways to break up components
• Different reservoirs can be considered

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Water (Mass) Balance

• Principal components
• Precipitation
• Evaporation
• Transpiration
• Runoff
• P E T Ro Change in Storage
• Units?

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Ground Water (Mass) Balance

• Principal components
• Recharge
• Inflow
• Transpiration
• Outflow
• R Qin T Qout Change in Storage