Environmental Science: Toward a Sustainable Future Richard T. Wright Chapter 7 Water: Hydrologic Cycle and Human Use PPT by Clark E. Adams
TEST 12/12/07 n HOMEWORK q ALSO DUE REVIEW QUESTIONS n 1 -10
Water: Hydrologic Cycle and Human Use—CHAPTER OBJECTIVES n n Water: a vital resource Hydrologic cycle: natural cycle, human impacts Water: a resource to manage, a threat to control Water stewardship: public-policy challenges
Practice Question? n How much of the Earth is covered with water? n 71% of the Earth Surface is covered with water, 98% of which is salt water we can not drink.
Water: A Vital Resource
Hydrologic Cycle: Natural Cycle, Human Impacts n n n Evaporation, condensation, purification Precipitation Groundwater Pools and fluxes in the cycle Human impacts on the hydrologic cycle
Temperature Determines Whether Water Is a n n n Gas: steam Liquid: running water Solid: ice q Why does ice float?
Basic Facts n n n Warm Air Rises--EVAPORATION Cool Air Falls Creates a Cycle of Moving Air Convection Current Warm air holds more water vapor molecules than cool air.
Precipitation n Adiabatic cooling: warm air rises, expands and cools 100% relative humidity + cooling = clouds Increasing condensation = water droplets
Global Precipitation n n Global precipitation distribution depends on patterns of rising and falling air currents Two main factors: q q global convection currents rain shadow effect
The Water Cycle
Practice Question? n Use the following slide to test your knowledge of the hydrologic cycle. q Label your notes n A. n D. n G. B. E. H. C. F.
Water Cycle Review B A D C E F H G
Global Air Circulation
Rain Shadow Effect
Water Balance in the Hydrologic Cycle
Pools and Fluxes in the Cycle D C I E Surface runoff loop F B Ground water H loop A G Evapotranspiration loop
Human Impacts on the Water Cycle n n n Changing the Earth’s surface Floods Climate change Atmospheric pollution Withdrawing water supplies
Groundwater n n n Decreased infiltration Increased runoff Decreased groundwater recharge
Human Impacts on the Hydrologic Cycle
Water: A Resource to Manage, A Threat to Control n n Uses and sources Surface waters
Municipal Water Use and Treatment What is your community’s water source?
Surface Waters n n Dam impacts (see Fig. 7 -15) Ecological effects of changing salinity in estuaries q q q Increased salinity Loss of native species Invasive species increase
Consequences of Overdrawing Groundwater n n Falling water tables Diminishing surface waters (wetlands) Land subsidence (see Fig. 7 -17) Saltwater intrusion
Aquifer Exploitation n n Groundwater use exceeds aquifer recharge Many remaining aquifers are heavily polluted
Water Stewardship: Public-Policy Challenges n n Obtaining more water Groundwater Using less water Public-policy challenges
Dams n Three Gorges Dam q q Largest in world Controls deadly floods Displaced 1. 2 million people including farms, cities, homes, and factories 370 -mile-long reservoir
Dams: Disrupt Integrity of River System n Above the dam q q q n Flooding Sediment deposition Loss of functional floodplain Below the dam q q q Loss of normal river flow patterns Loss of river biota Loss of functional floodplain
Using Less Water n Irrigation q q n Surge flow Drip irrigation $$$$ Municipal uses q q Incentives and regulations limiting water use Gray water
Desalting Seawater n n Reverse osmosis Distillation
National Water Policy n n Promote water efficiency Reduce or eliminate water subsidies Charge polluters Add watershed management to pricing of water
National Water Policy n n n United States must respond to global water crisis United States must reduce emission of greenhouse gases Need more data for informed policy decisions
End of Chapter 7