1. Water: Hydrologic Cycle and Human Use

2. Water: A Vital Resource

3. Polarity in H 2 O: The Water Molecule O HH ++ -- covalent bond

4. Condensation O HH ++ -- O HH ++ -- O HH ++ --

5. Evaporation and Condensation Evaporation – liquid  gas  Purifies water Condensation – gas  liquid  Forms precipitation and clouds The process of evaporation and condensation provides all the fresh water on the planet

6. Condensation

7. Relative Humidity Low temperature holds less water than high temperature  Winter air is drier Amount of humidity that air can hold is relative to temperature

8. Effects of Temperature on Water Temperature (kinetic energy) counteracts the effect of hydrogen bonds  Gas: steam, water vapor Individual water molecules  Liquid: running water  Solid: ice 0°C, 32°F Why does ice float?

9. The Water Cycle

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

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

12. Global Air Circulation

13. Rain Shadow Effect

15. Water Balance in the Hydrologic Cycle

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

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. Surface Waters Dam impacts Ecological effects of changing salinity in estuaries  Increased salinity  Loss of native species  Invasive species increase

21. 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

24. 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  Loss of functional floodplain

25. Grand Coulee Dam Along Columbia River Washington

26. Hoover Dam Along Colorado River Border of Arizona and Nevada

27. Consequences of Overdrawing Groundwater Falling water tables Diminishing surface waters (wetlands) Land subsidence (sink holes) Saltwater intrusion

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

29. Saltwater Intrusion

31. Desalting Seawater Reverse osmosis Distillation

32. Using Less Water Irrigation – greatest use  Surge flow – computer controlled irrigation  Drip irrigation – very expensive to install Municipal uses  Incentives and regulations limiting water use  Gray water recycling