Water Scarcity: The Global Crisis of Freshwater Management, Slides of Ecology and Environment

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Water Resources and Water

Pollution

Chapter 11

Freshwater is an irreplaceable resource that we

are managing poorly

• Freshwater is relatively pure and contains few

dissolved salts.

• Earth has a precious layer of water—most of it

saltwater—covering about 71% of the earth’s

surface.

• Water is an irreplaceable chemical with unique

properties that keep us and other forms of life

alive. A person could survive for several weeks

without food, but for only a few days without

water.

Freshwater is an irreplaceable resource that we

are managing poorly

• Concerns regarding water include:
  • Access to freshwater is a global health issue. Every day an average of 3,900 children younger than age 5 die from waterborne infectious diseases.
  • An economic issue – vital for reducing poverty and producing food and energy.
  • A women’s and children’s issue in developing countries because poor women and girls often are responsible for finding and carrying daily supplies of water.

Freshwater is an irreplaceable resource that we

are managing poorly

• A national and global security issue because of increasing tensions within and between nations over access to limited water resources that they share.
• An environmental issue because excessive withdrawal of water from rivers and aquifers results in dropping water tables, lower river flows, shrinking lakes, and losses of wetlands.

Most of the earth’s freshwater is not available to us

• The world’s freshwater supply is continually

collected, purified, recycled, and distributed in

the earth’s hydrologic cycle, except when:

• Overloaded with pollutants.
• We withdraw water from underground and surface water supplies faster than it is replenished.
• We alter long-term precipitation rates and distribution patterns of freshwater through our influence on projected climate change.

Most of the earth’s freshwater is not available to us

• Freshwater is not distributed evenly.
  • Differences in average annual precipitation and economic resources divide the world’s continents, countries, and people into water haves and have- nots.
  • Canada, with only 0.5% of the world’s population, has 20% of the world’s liquid freshwater, while China, with 19% of the world’s people, has only 7% of the supply.

Groundwater and surface water are

critical resources

• Aquifers: underground caverns and porous layers of sand, gravel, or bedrock through which groundwater flows—typically moving only a meter or so (about 3 feet) per year and rarely more than 0.3 meter (1 foot) per day.
• Watertight layers of rock or clay below such aquifers keep the water from escaping deeper into the earth.

Groundwater and surface water are critical resources

• Surface water is the freshwater from precipitation

and snowmelt that flows across the earth’s land

surface and into lakes, wetlands, streams, rivers,

estuaries, and ultimately to the oceans.

• Precipitation that does not infiltrate the ground or return to the atmosphere by evaporation is called surface runoff.
• The land from which surface water drains into a particular river, lake, wetland, or other body of water is called its watershed, or drainage basin.

We use a large and growing portion of the world’s reliable runoff

• Worldwide, about 70% of the water we

withdraw each year comes from rivers, lakes,

and aquifers to irrigate cropland, industry uses

another 20%, and residences 10%.

• Affluent lifestyles require large amounts of

water.

Freshwater shortages will grow

• The main factors that cause water scarcity in any

particular area are a dry climate, drought, too

many people using a water supply more quickly

than it can be replenished, and wasteful use of

water.

• More than 30 countries—mainly in the Middle

East and Africa—now face water scarcity.

• By 2050, 60 countries, many of them in Asia, with

three-fourths of the world’s population, are likely

to be suffering from water stress.

Groundwater is being withdrawn faster than it is

replenished in some areas

• Aquifers provide drinking water for nearly half of

the world’s people.

• Most aquifers are renewable resources unless their

water becomes contaminated or is removed faster

than it is replenished by rainfall.

• Water tables are falling in many areas of the world

because the rate of pumping water from aquifers

(mostly to irrigate crops) exceeds the rate of natural

recharge from rainfall and snowmelt.

Groundwater is being withdrawn faster than it is

replenished in some areas

• The world’s three largest grain producers—China, India, and the United States—as well as Mexico, Saudi Arabia, Iran, Yemen, Israel, and Pakistan are overpumping many of their aquifers.

Overpumping of aquifers has several harmful effects

• Groundwater overdrafts near coastal areas can

pull saltwater into freshwater aquifers. The

resulting contaminated groundwater is

undrinkable and unusable for irrigation.

• Deep water aquifers hold enough freshwater to

support billions of people for centuries.

• Concerns about tapping these ancient deposits of

freshwater:

• They are nonrenewable and cannot be replenished on a human timescale.

Overpumping of aquifers has several

harmful effects

• Little is known about the geological and ecological impacts of pumping large amounts of freshwater from deep aquifers.
• Some deep aquifers flow beneath more than one country and there are no international treaties that govern rights to them. Without such treaties, water wars could break out.
• The costs of tapping deep aquifers are unknown and could be high.