Chapter 14

Part 1

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Water keeps us alive, moderates climate, sculpts the land, removes and dilutes wastes and pollutants, and moves continually through the hydrologic cycle.

• Only about 0.02% of the earth’s water supply is available to us as liquid freshwater.

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Comparison of population sizes and shares of the world’s freshwater among the continents.

Figure 14-2Figure 14-2

Fig. 14-2, p. 307

ContinentPercent of world's water resources and population

Asia 60.5%

36%

Africa10%

8%Europe

North and Central America 7.3%

South America and Caribbean 6.4%

26%

15%

5%Oceania

11.3%

0.5%

14%

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Some precipitation infiltrates the ground and is stored in soil and rock (groundwater).

• Water that does not sink into the ground or evaporate into the air runs off (surface runoff) into bodies of water.– The land from which the surface water drains into a

body of water is called its watershed or drainage basin.

Fig. 14-3, p. 308

Unconfined Aquifer Recharge Area

Precipitation Evaporation and transpiration Evaporation

Confined Recharge Area

Runoff

Flowing artesian well

Recharge Recharge Unconfined Unconfined AquiferAquifer

Stream Well requiring a pumpInfiltration Water

table LakeInfiltration

Unconfined aquifer

Confined aquiferConfining impermeable rock layer Confining impermeable rock layer

Less permeable Less permeable material such as claymaterial such as clay

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• We currently use more than half of the world’s reliable runoff of surface water and could be using 70-90% by 2025.

• About 70% of the water we withdraw from rivers, lakes, and aquifers is not returned to these sources.

• Irrigation is the biggest user of water (70%), followed by industries (20%) and cities and residences (10%).

Case Study: Freshwater Resources in the United States

• 17 western states by 2025 could face intense conflict over scarce water needed for urban growth, irrigation, recreation and wildlife.

Figure 14-5Figure 14-5

Fig. 14-5, p. 310

Wash.

MontanaOregon

N.D.

IdahoWyoming S.D.

Nevada Neb.

UtahColo.

Kansas

California Oak.

N.M.Texas

Highly likely conflict potential

Moderate conflict potentialUnmet rural water needs

Substantial conflict potential

TOO LITTLE FRESHWATER• About 41% of the world’s population lives in

river basins that do not have enough freshwater.

• Many parts of the world are experiencing:– Rivers running dry.– Lakes and seas shrinking.– Falling water tables from overpumped aquifers.

Case Study: Who Should Own and Manage Freshwater Resources

• There is controversy over whether water supplies should be owned and managed by governments or by private corporations.

• European-based water companies aim to control 70% of the U.S. water supply by buying up water companies and entering into agreements with cities to manage water supplies.

TOO LITTLE FRESHWATER• Cities are outbidding farmers for water

supplies from rivers and aquifers.• Countries are importing grain as a way to

reduce their water use.• More crops are being used to produce

biofuels.• Our water options are:

– Get more water from aquifers and rivers, desalinate ocean water, waste less water.

WITHDRAWING GROUNDWATER TO INCREASE SUPPLIES

• Most aquifers are renewable resources unless water is removed faster than it is replenished or if they are contaminated.

• Groundwater depletion is a growing problem mostly from irrigation.– At least one-fourth of the farms in India are being

irrigated from overpumped aquifers.

Other Effects of Groundwater Overpumping

• Groundwater overpumping can cause land to sink, and contaminate freshwater aquifers near coastal areas with saltwater.

Figure 14-11Figure 14-11

Other Effects of Groundwater Overpumping

• Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater.

Figure 14-10Figure 14-10

Fig. 14-12, p. 316

Solutions

Groundwater Depletion

Prevention Control

Waste less water Raise price of water to discourage waste

Subsidize water conservation

Ban new wells in aquifers near surface waters

Tax water pumped from wells near surface waters

Buy and retire groundwater withdrawal rights in critical areas

Do not grow water-intensive crops in dry areas

Set and enforce minimum stream flow levels