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

Connections between water resources and food resources

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

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)

Water Usage Pie Chart

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).

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

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

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

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 1963. Lake Powell behind the dam is the second largest reservoir in the United States. Fig. 13-2, p. 317

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

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

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

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

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

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

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

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)

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

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. 13-13a, p. 328

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

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 2009. 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. 13-17, p. 332

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

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

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. 13-26, p. 341

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. 13-25a, p. 340

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. 13-25b, p. 340

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.