Key Concepts
• The hydrologic cycle is the sequence by which water moves between the
atmosphere and Earth’s surface: water falls to the land as precipitation; is
absorbed or runs off to rivers, streams, and eventually the ocean; and then
returns to the atmosphere as evaporation.
• A watershed is an area of land that water flows over or through on its way to
a larger body of water. The Bay Area is made up of several watersheds, one
of which takes water flowing from the Sierra Nevada mountain range to the
Pacific Ocean through a vast system of pipes, pumps, and tunnels.
• Only a small fraction of freshwater is available for human consumption.
In California, which is prone to a dry climate and drought years, water is
a particularly limited resource. (From NGSS ESS3.A)
• One source of renewable power comes from harnessing the energy of moving
water and converting it into electricity. This is called hydroelectric power.
• Other power sources include solar energy, wind energy, and the burning of
fossil fuels that were formed from the remains of once-living organisms.
BIG IDEAS
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Grades 6–8
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SAN FRANCISCO PUBLIC UTILITIES COMMISSION
53