Water, water everywhere and not a drop to drink!

3.6 Water Resources

Connections between water resources and food resources

Earth’s water budgetOnly 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 waterThe remaining 1% is lakes rivers swamps

and in the atmosphere

Human Uses for Fresh waterDomestic water ( drinking, washing,

cleaning)IrrigationIndustry (manufacturing, mining, andagriculture)Hydroelectric powerTransportation (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. statesSupplies water and electricity ~30 million people

in USA and MexicoHeavily dammed for electricity and agriculture

(14 dams)80% used for irrigation and cattle ranchingDownstream (in Mexico) can dry up completely

some years and lead to droughts.Salinity problems prevent irrigation in MexicoDried river causes loss of biodiversity

The Colorado River Basin

Fig. 13-1, p. 317

Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell

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, riceWater use subsidized by government

ReservoirsLeak water into ground belowLose much water through evaporationFill up with silt load of river, depriving deltaCould eventually lose ability to store water and

create electricityStates must conserve water, control population,

and slow urban development

Water Shortages Will GrowDry climatesDroughtToo many people using a normal supply of

waterWasteful use of water30% earth’s land area experiences severe

droughtPotential conflicts/wars over water

Refugees from arid landsIncreased mortality

Fig. 13-5, p. 322

Washington

OregonMontana

North Dakota

Idaho South DakotaWyoming

NevadaNebraska

Utah Colorado Kansas

California Oklahoma

ArizonaNew Mexico

Texas

Highly likely conflict potential

Substantial conflict potential

Moderate conflict potential

Unmet rural water needs

Natural Capital Degradation: Stress on the World’s Major River Basins

Fig. 13-6, p. 323

Is Extracting Groundwater the Answer? Groundwater is Being Withdrawn Faster Than It Is

ReplenishedMost aquifers are renewableAquifers provide drinking water for half the worldWater tables are falling in many parts of the world,

primarily from crop irrigation

Water: A Replenishable ResourceIndia, China, and the United States

Three largest grain producersOver pumping aquifers for irrigation of cropsSmall farmers drilling tube wells Effect on water table

Saudi ArabiaAquifer depletion and irrigation

Fig. 13-7, p. 325

Trade-Offs

Withdrawing Groundwater

Advantages Disadvantages

Useful for drinking and irrigation

Aquifer depletion from overpumping

Exists almost everywhere

Sinking of land from over pumping

Renewable if not overpumped or contaminated

Pollution of aquifers lasts decades or centuries

Deeper wells are nonrenewable

Cheaper to extract than most surface waters

Is Building More Dams the Answer?

Main goal of a dam and reservoir systemCapture and store runoffRelease runoff as needed to control:

FloodsGenerate electricitySupply irrigation waterRecreation (reservoirs)

Advantages and Disadvantages of Dams

AdvantagesReduce floodingZero emissions electricity production

DisadvantagesDisplaces people with reservoir Impaired ecological services of riversLoss of plant and animal speciesCan cause other streams and lakes to dry up

Fig. 13-13a, p. 328

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)

Reduces down-stream flooding of cities and farms

Disrupts migration and spawning of some fish

Is irrigation the answer? Case Study: The Aral Sea DisasterLarge-scale water transfers for irrigation

stops flow of water into the Aral SeaLess Water = Increase in salinityFish population declinesWater pollutionRestoration efforts

More efficient irrigationDam built to help raise lake level

Natural Capital Degradation: The Aral Sea, Shrinking Freshwater Lake

Fig. 13-17, p. 332

Is Desalination the Answer? Desalination- Removing Salt from

Seawater Distillation: evaporate water, leaving salts

behindReverse osmosis, microfiltration: use high

pressure to remove saltsProblems: Very Costly, Kills Organisms,

Creates Briny Wastewater14,450 plants in 125 countries

Saudi Arabia: highest number

The Search for Improved Desalination Technology

Desalination on offshore shipsSolar or wind energy

Use ocean waves for powerBuild desalination plants near electric power

plants

Deforestation Above China’s Yangtze River Contribute to Erosion and Floods

Fig. 13-26, p. 341

Fig. 13-25a, p. 340

Diverse ecological habitat

Evapotranspiration

Trees reduce soil erosion from heavy rain and wind

Agricultural land

Tree roots stabilize soil

Vegetation releases water slowly and reduces floodingForested Hillside

Fig. 13-25b, p. 340

Tree plantation

Roads destabilize hillsides Overgrazing accelerates soil

erosion by water and wind

Evapotranspiration decreases

Winds remove fragile topsoil

Agricultural land is flooded and silted up

Gullies and landslides

Heavy rain erodes topsoil

Silt from erosion fills rivers and reservoirs Rapid runoff causes flooding

After Deforestation

Three Big Ideas1. One of the world’s major environmental problems is

the growing shortage of freshwater in many parts of the world.

2. 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.

3. 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.