1. Water, water everywhere and not a drop to drink!
3.6 Water Resources
Water, water everywhere and not a drop to drink!

2. Connections between water resources and food resources

3. Earth’s water budget
Only about 3% of the water on our planet is fresh water (97% salt water)
69% of fresh water is in polar ice caps and glaciers
30% is ground water
The remaining 1% is lakes rivers swamps and in the atmosphere

5. Human Uses for Fresh water
Domestic water ( drinking, washing, cleaning)
Irrigation
Industry (manufacturing, mining, and
agriculture)
Hydroelectric power
Transportation (ships on lakes/rivers)
Boundaries (states and nations)

6. Water Usage Pie Chart

7. Problems related to freshwater use
Low water levels in rivers, streams and lakes
Slow water flow
Underground aquifers become exhausted
Irrigation causes much of the water to evaporate before it can be used.
Fertilizer and pesticides and industries pollute streams
Industries release warm water into rivers, causes dissolved oxygen to decrease (warm water contains less Oxygen).

8. Solutions
Reduce domestic use of fresh water (shorter showers/wash cars less…)
Irrigation: Drought resistant crops- Closed pipes instead of open canals
Reduce farming contamination (pesticides and fertilizers).
Force industry to remove pollutants from wastewater

9. Case Study: The Colorado River: An Over tapped Resource
1,429 miles through 7 U.S. states
Supplies water and electricity ~30 million people in USA and Mexico
Heavily dammed for electricity and agriculture (14 dams)
80% used for irrigation and cattle ranching
Downstream (in Mexico) can dry up completely some years and lead to droughts.
Salinity problems prevent irrigation in Mexico
Dried river causes loss of biodiversity

10. The Colorado River Basin
Figure 13.1: The Colorado River basin: The area drained by this basin is equal to more than one-twelfth of the land area of the lower 48 states. Two large reservoirs—Lake Mead behind the Hoover Dam and Lake Powell behind the Glen Canyon Dam—store about 80% of the water in this basin.
Fig. 13-1, p. 317

11. Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell
Figure 13.2: The Glen Canyon Dam across the Colorado River was completed in Lake Powell behind the dam is the second largest reservoir in the United States.
Fig. 13-2, p. 317

12. A Closer Look at the Over tapped Colorado River Basin
Current rate of river withdrawal is not sustainable
Much water used for agriculture that is inefficient with water use: cotton, alfalfa, rice
Water use subsidized by government
Reservoirs
Leak water into ground below
Lose much water through evaporation
Fill up with silt load of river, depriving delta
Could eventually lose ability to store water and create electricity
States must conserve water, control population, and slow urban development

13. Water Shortages Will Grow
Dry climates
Drought
Too many people using a normal supply of water
Wasteful use of water
30% earth’s land area experiences severe drought
Potential conflicts/wars over water
Refugees from arid lands
Increased mortality

14. Washington North Dakota Montana Oregon Idaho South Dakota Wyoming
Nebraska
Nevada
Utah
Colorado
Kansas
California
Oklahoma
New Mexico
Arizona
Figure 13.5: This map shows water scarcity hotspots in 17 western states that, by 2025, could face intense conflicts over scarce water needed for urban growth, irrigation, recreation, and wildlife. Some analysts suggest that this is a map of places not to live in the foreseeable future. Question: Which, if any, of these areas are found in the Colorado River basin (Figure 13-1)? (Data from U.S. Department of the Interior)
Texas
Highly likely conflict potential
Substantial conflict potential
Moderate conflict potential
Unmet rural water needs
Fig. 13-5, p. 322

15. Natural Capital Degradation: Stress on the World’s Major River Basins
Figure 13.6: Natural capital degradation.
The world’s major river basins differ in their degree of water scarcity stress, the measurement of which is based on a comparison of the amount of water available with the amount used by humans (Concept 13-1B). Questions: If you live in a water-stressed area, what signs of stress have you noticed? In what ways, if any, has it affected your life? (Data from World Commission on Water Use in the 21st Century)
Fig. 13-6, p. 323

16. Is Extracting Groundwater the Answer?
Groundwater is Being Withdrawn Faster Than It Is Replenished
Most aquifers are renewable
Aquifers provide drinking water for half the world
Water tables are falling in many parts of the world, primarily from crop irrigation

17. Water: A Replenishable Resource
India, China, and the United States
Three largest grain producers
Over pumping aquifers for irrigation of crops
Small farmers drilling tube wells
Effect on water table
Saudi Arabia
Aquifer depletion and
irrigation

18. Withdrawing Groundwater
Trade-Offs
Withdrawing Groundwater
Advantages
Disadvantages
Useful for drinking and irrigation
Aquifer depletion from overpumping
Sinking of land from over pumping
Exists almost everywhere
Renewable if not overpumped or contaminated
Pollution of aquifers lasts decades or centuries
Figure 13.7: Withdrawing groundwater from aquifers has advantages and disadvantages. Questions: Which two advantages and which two disadvantages do you think are the most important? Why?
Cheaper to extract than most surface waters
Deeper wells are nonrenewable
Fig. 13-7, p. 325

19. Is Building More Dams the Answer?
Main goal of a dam and reservoir system
Capture and store runoff
Release runoff as needed to control:
Floods
Generate electricity
Supply irrigation water
Recreation (reservoirs)

20. Advantages and Disadvantages of Dams
Reduce flooding
Zero emissions electricity production
Disadvantages
Displaces people with reservoir
Impaired ecological services of rivers
Loss of plant and animal species
Can cause other streams and lakes to dry up

21. Provides irrigation water above and below dam
Flooded land destroys forests or cropland and displaces people
Large losses of water through evaporation
Provides water for drinking
Deprives downstream cropland and estuaries of nutrient-rich silt
Reservoir useful for recreation and fishing
Risk of failure and devastating downstream flooding
Can produce cheap electricity (hydropower)
Figure 13.13: Trade-offs.
Large dams and reservoirs have advantages (green) and disadvantages (orange) (Concept 13-3). The world’s 45,000 large dams (15 meters (49 feet) or higher) capture and store about 14% of the world’s surface runoff, provide water for almost half of all irrigated cropland, and supply more than half the electricity used in 65 countries. The United States has more than 70,000 large and small dams, capable of capturing and storing half of the country’s entire river flow. Question: Which single advantage and which single disadvantage do you think are the most important?
Reduces down-stream flooding of cities and farms
Disrupts migration and spawning of some fish
Fig a, p. 328

22. Is irrigation the answer?
Case Study: The Aral Sea Disaster
Large-scale water transfers for irrigation stops flow of water into the Aral Sea
Less Water = Increase in salinity
Fish population declines
Water pollution
Restoration efforts
More efficient irrigation
Dam built to help raise lake level

23. Natural Capital Degradation: The Aral Sea, Shrinking Freshwater Lake
Figure 13.17: Natural capital degradation.
The Aral Sea was one of the world’s largest saline lakes. Since 1960, it has been shrinking and getting saltier because most of the water from the two rivers that replenish it has been diverted to grow cotton and food crops. These satellite photos show the sea in 1976 and in As the Southern Aral Sea shrank, it split into two lakes and left behind a salty desert, economic ruin, increasing health problems, and severe ecological disruption. By late 2009, the larger eastern part of the once huge Southern Aral Sea was gone (bottom-right part of each photo). The smaller Northern Aral Sea (top of each photo) has also shrunk, but not nearly as much as the Southern Aral Sea has. Question: What are three things that you think should be done to help prevent further shrinkage of the Aral Sea?
Fig , p. 332

24. Is Desalination the Answer?
Desalination- Removing Salt from Seawater
Distillation: evaporate water, leaving salts behind
Reverse osmosis, microfiltration: use high pressure to remove salts
Problems: Very Costly, Kills Organisms, Creates Briny Wastewater
14,450 plants in 125 countries
Saudi Arabia: highest number

25. The Search for Improved Desalination Technology
Desalination on offshore ships
Solar or wind energy
Use ocean waves for power
Build desalination plants near electric power plants

26. Deforestation Above China’s Yangtze River Contribute to Erosion and Floods
Figure 13.26: Deforestation of hills and mountains in China’s Yangtze River Basin contributed to increased flooding, topsoil erosion, and the flow of eroded sediment into the Yangtze River. Because of these harmful effects, China stopped the deforestation and established a massive tree-planting program to reforest the degraded land.
Fig , p. 341

27. Diverse ecological habitat Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Agricultural land
Figure 13.25: Natural capital degradation.
These diagrams show a hillside before and after deforestation. Once a hillside has been deforested for timber, fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding and pollution in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.” See an animation based on this figure at CengageNOW. Question: How might a drought in this area make these effects even worse?
Tree roots stabilize soil
Vegetation releases water slowly and reduces flooding
Forested Hillside
Fig a, p. 340

28. Evapotranspiration decreases Roads destabilize hillsides
Tree plantation
Evapotranspiration decreases
Roads destabilize hillsides
Overgrazing accelerates soil erosion by water and wind
Winds remove fragile topsoil
Agricultural land is flooded and silted up
Gullies and landslides
Figure 13.25: Natural capital degradation.
These diagrams show a hillside before and after deforestation. Once a hillside has been deforested for timber, fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding and pollution in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.” See an animation based on this figure at CengageNOW. Question: How might a drought in this area make these effects even worse?
Heavy rain erodes topsoil
Silt from erosion fills rivers and reservoirs
Rapid runoff causes flooding
After Deforestation
Fig b, p. 340

29. Three Big Ideas
One of the world’s major environmental problems is the growing shortage of freshwater in many parts of the world.
We can increase water supplies in water-short areas in a number of ways, but the most important way is to reduce overall water use and waste by using water more sustainably.
We can use water more sustainably by cutting water waste, raising water prices, slowing population growth, and protecting aquifers, forests, and other ecosystems that store and release water.