1. Environmental Science: Toward a Sustainable Future Richard T. Wright
Chapter 9
Water: Hydrologic Cycle and Human Use
PPT by Clark E. Adams

2. Water: Hydrologic Cycle and Human Use
Water: a vital resource
Hydrologic cycle: natural cycle, human impacts
Water: a resource to manage, a threat to control
Water stewardship: public-policy challenges

3. Water: A Vital Resource

4. Hydrologic Cycle: Natural Cycle, Human Impacts
Evaporation, condensation, purification
Precipitation
Groundwater
Pools and fluxes in the cycle
Human impacts on the hydrologic cycle

5. Polarity in H2O: The Water Molecule+ -
covalent bond

6. Condensation O H + - O H + - O H + -

7. Temperature Determines Whether Water Is a
Gas: steam
Liquid: running water
Solid: ice
Why does ice float?

8. The Water Cycle

9. Water Cycle Review B A D C E F H G

10. Condensation

11. Precipitation Adiabatic cooling: warm air rises, expands and cools
100% relative humidity + cooling = clouds
Increasing condensation = water droplets

12. Global Precipitation
Global precipitation distribution depends on patterns of rising and falling air currents
Two main factors:
global convection currents
rain shadow effect

13. Global Air Circulation

14. Rain Shadow Effect

15. Water Balance in the Hydrologic Cycle

16. Pools and Fluxes in the CycleB G I F
Ground water
loop
Surface runoff
Evapotranspiration C E D H

17. Human Impacts on the Water Cycle
Changing the Earth’s surface
Floods
Climate change
Atmospheric pollution
Withdrawing water supplies

18. Groundwater Decreased infiltration Increased runoff
Decreased groundwater recharge

19. Human Impacts on the Hydrologic Cycle

20. Water: A Resource to Manage, A Threat to Control
Uses and sources
Surface waters

21. Water Uses

22. Water Uses

23. Municipal Water Use and Treatment What is your community’s
water source?

24. Surface Waters Dam impacts (see Fig. 7-15)
Ecological effects of changing salinity in estuaries
Increased salinity
Loss of native species
Invasive species increase

25. Consequences of Overdrawing Groundwater
Falling water tables
Diminishing surface waters (wetlands)
Land subsidence (see Fig. 7-17)
Saltwater intrusion

26. Aquifer Exploitation Groundwater use exceeds aquifer recharge
Many remaining aquifers are heavily polluted

27. Saltwater Intrusion

28. Water Stewardship: Public-Policy Challenges
Obtaining more water
Groundwater
Using less water
Public-policy challenges

29. Dams Three Gorges Dam Largest in world Controls deadly floods
Displaced 1.2 million people including farms, cities, homes, and factories
370-mile-long reservoir

30. Dams: Disrupt Integrity of River System
Above the dam
Flooding
Sediment deposition
Loss of functional floodplain
Below the dam
Loss of normal river flow patterns
Loss of river biota

31. Using Less Water Irrigation Municipal uses Surge flow
Drip irrigation $$$$
Municipal uses
Incentives and regulations limiting water use
Gray water

32. Desalting Seawater
Reverse osmosis
Distillation

33. Public-Policy Challenges

34. National Water Policy Promote water efficiency
Reduce or eliminate water subsidies
Charge polluters
Add watershed management to pricing of water

35. National Water Policy
United States must respond to global water crisis
United States must reduce emission of greenhouse gases
Need more data for informed policy decisions

36. End of Chapter 7