Environmental Science 102
Hydrosphere and Hydrologic Cycles


2 hydrogen, 1 oxygen - H2O
Phase changes from one state to another involve the exchange of latent heat and a temperature change
Solid to Liquid - melting
Liquid to Solid - freezing
Liquid to Gas - evaporation
Gas to Liquid - condensation
Gas to Solid - deposition
Solid to Gas - Sublimation
Solid water (ice) is a mineral according to the geologic definition of a mineral - it has a crystalline structure and definite chemical composition and occurs naturally.
Ice is unusual in that its density is less than liquid water, thus it floats in water.


Oceans contain 97.2% of the world's water supply
Fresh water makes up the remaining 2.80%
Of this fresh water, it is found in the following sources and amounts:
- Ice/Glaciers - 2.15%
- Groundwater - 0.63%
- Surface water - 0.023 %
Of this surface water, it is found in the following sources and amounts:
- Fresh water lakes - 0.009%
- Saline lakes and seas - 0.008%
- Soil water - 0.005%
- Atmosphere - 0.001%
- Streams - 0.0001%

Total volume of water = 1.5 billion km3
If the entire Earth were smooth and covered with water, the depth of the water would be 2700 m.

Hydrologic Cycle

This cycles describes where water is found (reservoirs) and the global and local flow of water among its reservoirs.
Four main aspects of this cycle are:
- Evaporation - movement of water from the surface (land and water) to the atmosphere
- Transportation - movement of water (liquid and gas) in the atmosphere by wind motion
- Precipitation - removal of water from the atmosphere to the surface in either liquid or solid form
- Runoff - movement of water as either surface flow or groundwater flow - ultimate destination of all runoff is the ocean.

Global Water Balance

Similar to the Global Energy Balance but involves movement of water.
Total evaporation = total precipitation

Human Influence and Disruption of the Hydrologic Cycle

Class Discussion
How does or can human influence increase or decrease the amount of evaporation, precipitation, and runoff?