Transcript Hydrologic Cycle and Human Use

CHAPTER 10
Water: Hydrologic
Cycle and Human Use
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Introduction to water
• The former Soviet Union was responsible for the
death of the Aral Sea in Central Asia
• It was once the fourth largest lake on Earth
• Two rivers were tapped for irrigation for cotton
• Eliminating inflow of water into the Aral
• The Aral Sea began to shrink
• The commercial fishery collapsed
• 60,000 fishermen lost their jobs
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The shrinking Aral Sea
• The lake lost 90% of its volume
• The water level dropped by 53 feet
• The surface area shrunk greatly
• The sea separated into the southern Big Aral and
the northern Small Aral
• The Big Aral is too salty for fish
• Windblown salt and dust cause asthma and
cancer
• The climate has changed
• Unique animals have gone extinct
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Regime change
• The future of the Aral Sea is in the hands of
Uzbekistan, Kazakhstan, Turkmenistan, Tajikistan,
and Kyrgyzstan
• Struggling countries that use water for irrigation
• There is little hope of restoring the Aral Sea
• A restoration project is helping the Small Aral
• Only brine shrimp survive in the Big Aral
• The Rio Grande and Colorado rivers are drying up
• The Dead Sea is dying because of water diversion
• Domestic, industrial, and agricultural use compete
for limited water
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Water: a vital resource
• Water is fundamental to life
• Earth is flooded with water
• Covering 75% of the Earth’s surface
• 97.5% of all water is salt water (oceans, seas)
• Fresh water: contains < 0.1% (1,000 ppm) salt
• 67% of fresh water is bound up in ice caps and
glaciers
• Only 0.77% of all water is in lakes, wetlands,
rivers, groundwater, biota, soil, and the
atmosphere
• Evaporation and precipitation cycle water
through the solar-powered hydrologic cycle
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Earth’s water
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Freshwater is a renewable resource
• Streams, rivers, ponds, lakes, swamps, estuaries,
groundwater, bays, oceans, and atmosphere
contain water
• They represent ecosystem capital (goods and
services)
• Water is used for drinking, industries, irrigation,
energy, transportation, recreation, waste
processing, habitats
• Water modifies the climate
• Humans have constructed huge infrastructures to
control water
• Dams, canals, reservoirs, aqueducts, sewer systems
• Treatment plants, water towers, pipelines, irrigation
• Desalinization plants
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Water in developed and developing
nations
• Developed countries benefit from controlling water
• Controlling diseases, building cities in deserts,
irrigation, electricity
• Water in developing countries is costly or inaccessible
• They lack access to safe drinking water and sanitation
• People die from waterborne diseases
• Because of infrastructure to control water
• Seas and rivers are being lost
• Millions have been displaced to make room for
reservoirs
• Tensions increase for access to water
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Differences in availability
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Future challenges
• Increasing population will challenge water
management infrastructure
• Increasing agricultural output
• Cities and industries compete with agriculture
• Climate change will affect the hydrologic cycle
• Rainfall variability will cause floods and droughts
• There are two ways to consider water issues
• Quantity
• Quality
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Hydrologic cycle
• Hydrologic (water) cycle: the cycling of water
through the Earth
• Evaporation and transpiration: water rises to the
atmosphere
• Condensation and precipitation: water returns to the
land and oceans
• Green water: water in vapor form
• Blue water: water in liquid form
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The hydrologic cycle
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The hydrologic cycle
Animation: Hydrologic Cycle
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Water cycle scramble
Animation: Hydrologic Cycle
Scramble
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Evaporation
• Hydrogen bonding holds water molecules (H2O)
together
• Below freezing (32°F, 0°C): low kinetic energy
allows hydrogen bonding to hold molecules in
place as ice
• Above freezing but below boiling: the kinetic
energy allows hydrogen bonds to break and reform as liquid
• Evaporation: as water molecules absorb energy
from the Sun, kinetic energy allows molecules to
enter the atmosphere
• Water vapor: water molecules in the gaseous state
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Water vapor is a greenhouse gas
• Water vapor contributes two-thirds of the warming
of all greenhouse gases
• Humidity: amount of water vapor in the air
• Relative humidity: the amount of water vapor as a
percent of what the air can hold at a particular
temperature
• The amount of water vapor the air can hold varies
with the temperature
• Cooling causes water vapor to condense to liquid
water
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Condensation
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Condensation
• Condensation is the opposite of evaporation
• Water molecules rejoin by hydrogen bonding,
forming liquid water
• Fog and clouds: droplets forming in the atmosphere
• Dew: droplets forming on vegetation
• Aerosols: microscopic liquid or solid particles
• Help condensation occur
• Originate naturally from volcanoes, dust, soil, salt
• Human sources: sulfates, carbon, dust
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Purification
• Evaporation and condensation purify water naturally
• Evaporation removes only water molecules, not salts
and other solids
• Atmospheric water turns over every 10 days
• Water is constantly purified
• Evaporation and condensation are the source of all
fresh water
• Water eventually reaches the oceans, inland seas,
lakes
• Evaporation and transpiration return water to the
atmosphere
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Precipitation
• Warm, less dense air rises
• Adiabatic cooling: warm air gradually cools as it rises
and expands
• Adiabatic warming: occurs as cold air descends and
is compressed by higher air pressure
• Earth’s precipitation ranges from near zero to 2.5
meters (100 in.) per year
• The distribution depends on rising and falling air
currents
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Air currents affect precipitation
• Rising air cools and condenses
• Precipitation results
• Descending air warms, causing evaporation
• Dryness results
• A cold front causes warm, moist air in the area to
rise
• The cold air of the advancing front is denser
• The rising warm air cools and condenses and
precipitation occurs
• Global convection currents and rain shadows cause
rising and falling air currents and affect precipitation
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Global precipitation
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Convection currents
• Convection currents occur because the Sun heats
the Earth most intensely over and near the equator
• Heated air expands, rises, and cools
• Condensation and precipitation occur
• The equator’s constant heat causes this process to
repeat
• Supporting tropical rain forests
• The now dry air “spills over” north and south of the
equator
• Descending over subtropical areas and creating
deserts
• Hadley cell: the system composed of rising and
falling air
• Trade winds: Earth’s rotation deflects winds east
and west
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Hadley cells
Animation: Hadley Cells
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Global air circulation
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Rain shadow
• Moisture-laden trade winds encounter mountain
ranges
• The deflected air rises and cools and precipitation
occurs on the windward side of the mountains
• Air crossing the mountains warms and picks up
moisture
• Deserts occur on the leeward sides of mountains
• Rain shadow: the dry region downwind of a
mountain range
• Causes the severest deserts in the world
• For example, Death Valley, east of the Sierra
Nevada mountains in California
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Rain shadow
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Groundwater
• Precipitation can either soak into the ground
(infiltration) or run off the surface
• Infiltration-runoff ratio: the amount of water that
soaks into the ground compared with the amount
that runs off
• Runoff flows into streams and rivers, eventually
reaching oceans or inland seas
• Watershed: all the land area contributing to a
stream or river
• Surface waters: ponds, lakes, streams, rivers, etc.
on the Earth’s surface
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Infiltrating water has two alternatives
• Capillary water: held in the soil, according to the
soil’s capacity
• Returns to the atmosphere by evaporation or
transpiration (green water flow)
• Evapotranspiration: the combination of evaporation
and transpiration
• Gravitational water: is not held in the soil
• Percolation (blue water flow): trickling of water
through pores or cracks in the soil
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Groundwater and the water table
• Groundwater: water accumulated in the earth
• It lies on top of an impervious layer of rock or clay
• Water table: the upper surface of groundwater
• Gravitational water becomes groundwater when it
reaches the water table
• Wells dug below the water table allow groundwater
to seep into the well
• The groundwater fills the well to the level of the
water table
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Recharge
• Groundwater seeps laterally as it seeks its lowest
level
• Aquifers: layers of porous material through which
groundwater moves
• It is hard to determine the location of aquifers
• Layers of porous rock are found between layers of
impervious rock
• The entire formation may be fractured and folded
• Recharge area: the area where water enters an
aquifer
• May be miles away from where water leaves the
aquifer
• Aquifers hold 99% of all liquid water
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Underground purification
• As water percolates through the soil, debris and
bacteria are filtered out
• Water may dissolve or leach out minerals
• Some minerals can be dangerous (arsenic, sulfide,
etc.)
• Drawn by gravity, groundwater moves through
aquifers until it finds an opening to the surface
• Seep: water flows out in a wide area
• Spring: water flows from a small opening
• Seeps and springs feed streams, lakes, and rivers
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Loops, pools, and fluxes
• The hydrologic cycle has four physical processes:
evaporation, condensation, precipitation, and
gravitational flow
• It also has three major loops
• Evapotranspiration loop: green water that
evaporates and returns by precipitation
• The main source for ecosystems and natural
agriculture
• Held as capillary water
• It returns to the atmosphere by evapotranspiration
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Other loops of the hydrologic cycle
• Surface runoff loop: blue water across the
ground’s surface
• Becomes part of the surface water system
• Groundwater loop: blue water that infiltrates,
percolates, and joins groundwater
• Moves through aquifers and exits through seeps,
springs, and wells to rejoin surface water
• These two loops are the focus for human water
resource management
• The hydrologic cycles “fluxes”: the exchange of
water among land, atmosphere, and oceans
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Yearly water balance in the
hydrologic cycle
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Human impacts on the hydrologic cycle
• Many environmental problems stem from direct or
indirect impacts on the water cycle
• Four categories of impacts:
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Changes to Earth’s surface
Changes to Earth’s climate
Atmospheric pollution
Withdrawals for human use
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Changes to the surface of the Earth
• In natural systems, vegetation intercepts
precipitation
• Water infiltrates into porous topsoil, filtering out debris
• Evapotranspiration sustains ecosystems and recycles
water
• Recharged groundwater reservoirs release water
through springs and seeps into streams and rivers
• In cleared forests and overgrazed land, plants do
not intercept rainfall
• Water shifts from infiltration and recharge into runoff
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Cleared land affects the hydrologic
cycle
• Removing vegetation causes a sudden influx of
water into rivers and streams
• Causing floods, pollutants from erosion, and less
evapotranspiration and groundwater recharge
• Resulting in dry, barren, lifeless streambeds
• Wetlands also store and release water
• Destruction leads to flooding and polluted waterways
• Wetlands dry up during droughts
• In 2008, Iowa had massive flooding due to filling
wetlands and converting tallgrass prairies to
plowed fields
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Climate change
• There is unmistakable evidence that Earth is
warming
• Increasing greenhouse gases are changing the water
cycle
• Evaporation increases with a warmer climate
• A wetter atmosphere means more and heavier
precipitation and floods
• More hurricanes and droughts
• Water-stressed areas (e.g., East Africa) will get less
water
• Global warming may be speeding up the water cycle
• Affecting precipitation, evapotranspiration,
groundwater recharge, runoff, snowmelt, etc.
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Atmospheric pollution
• Aerosol particles form nuclei, enabling water to
condense into droplets
• More clouds form
• Anthropogenic particles are increasing
• From sulfates, carbon (soot), dust
• Form a brownish haze associated with industrial
areas, tropical burning, and dust storms
• Solar radiation is reduced
• Aerosols have a cooling effect
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Aerosols affect the water cycle
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They promote smaller droplets
They suppress rainfall, even though clouds form
Aerosols suppress atmospheric cleansing
They cause aerosols to remain in the air longer,
further increasing drier conditions
• Dust, smoke, and aerosols increase
• Aerosols work differently from greenhouse
gases
• Aerosols have more local (vs. global) impacts
• They do not accumulate—they have a lifetime of
days
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Water: management and control
• Humans use 27% of all accessible freshwater
runoff
• Global withdrawal will increase 10% each decade
• Americans use less water than in 1980
• Nonconsumptive uses of water: water may be
contaminated, but is still available to humans
• Used in homes, industries, and electric power
production
• Consumptive uses of water: the applied water
does not return to the water resource
• It is gone from human control
• Water for irrigation
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U.S. trends in population and
freshwater withdrawals
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Uses of water
• Worldwide, the largest use is for irrigation
• Then industry and direct human use
• Use varies by region, depending on:
• Natural precipitation
• Degree of development
• Most increases in withdrawal are due to increases
in agriculture
• Irrigation accounts for 65% of freshwater
consumption in the U.S.
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Regional usage of water
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Sources of water
• 37% of domestic water comes from groundwater
sources
• 63% comes from surface water (rivers, lakes,
reservoirs)
• Rural people in developing nations get water where
they can
• Wells, rivers, lakes, rainwater
• Women often have to walk long distances to get water
• Water in developing nations is often polluted with
waste
• 1.1 billion people use polluted water
• 1.6 million (mostly children) die each year
• Millennium Development Goal 7: increase access to
safe drinking water
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Water in the developing world
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Technologies in developed nations
• Industrialized countries collect, treat, and distribute
water
• Larger municipalities rely mostly on surface water
• Dams create reservoirs to generate power and for
recreation, irrigation, flood control
• Water is piped to a treatment plant
• It is then distributed to homes, schools, industries
• After use, it is collected by the sewage system and
treated
• It is then released downstream into the same river
• Water is reused many times on major rivers (e.g.,
Mississippi)
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Municipal water use and treatment
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Technologies in other areas
• In developing nations, wastewater is often
discharged with little or no treatment
• Cities downstream have much higher pollution loads
• Ecosystems can be severely affected by pollution
• Smaller public drinking-water systems depend on
groundwater
• Water is purified by percolation
• Surface and groundwater represent a sustainable
or renewable (self-replenishing) resource
• But they can be overdrawn
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Surface waters
• The Glen Canyon Dam spans the Colorado River
• In Arizona, just above Grand Canyon National Park
• It stores excess water in Lake Powell
• Lake Powell is the second largest reservoir in the
U.S.
• It generates hydropower
• It stores water for Arizona, California, Nevada, Mexico
• Water released was strictly to maximize hydropower
• Its flow fluctuated during the day
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Glen Canyon Dam
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Glen Canyon Dam management
• An environmental impact study in the late 1980s
and early 1990s concluded that:
• The Glen Canyon Dam had seriously damaged the
downstream ecology of the Colorado river
• Recreational resources (hiking, rafting) were
damaged
• The Grand Canyon Protection Act (1992) required
“adaptive management”
• Adjust water release rates to enhance the ecological
and recreational values of the river
• The dam now meets ecological and social needs
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Dams and the environment
• Over 45,000 large dams (over 50 feet) exist
• Many reservoirs store billions of liters (billions of
gallons)
• Covering 49 million hectares (120 million acres)
• Only 31% of annual runoff is available for withdrawal
• Rivers are too remote
• Navigation, flood control, hydropower also need water
• Large dams have enormous social impacts
• Displacing 40 million people
• Preventing access to goods and services of the
buried ecosystems
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Dams have enormous impacts
• Valuable freshwater habitats (waterfalls, rapids, fish
runs) are lost
• The waterway below the diversion is deprived of
water
• Fish and other aquatic organisms are directly
impacted
• Wildlife is adversely affected (e.g., food chains)
• Wetlands dry up and waterfowl die
• Fish (e.g., salmon) cannot swim upstream to spawn
or downstream to return to the ocean
• Even with fish ladders to help them pass the dams
• Juvenile salmon suffer 95% mortality going to sea
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Ecological effects of diversion
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Dams gone
• People are recognizing the unacceptable costs of
dams
• 714 dams have been removed in the U.S.
• But removal is not easy
• There are legal complexities to dam removal
• Existing uses conflict with expected advantages
(establishing fish, recreational and aesthetic uses)
• There are practical problems to dam removal
• Built up sediment in the reservoir can be
contaminated
• Removing the Edwards Dam in Maine restored fish
species and recreational use of the Kennebec River
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Impacts on estuaries
• Estuaries: very productive ecosystems in bays and
rivers
• Where fresh river water mixes with seawater
• Breeding grounds for birds, fish, shellfish
• Decreased fresh water increases the water’s salinity
• In the San Francisco Bay, over 60% of freshwater
has been diverted for irrigation and municipal use
• Devastated the bay
• Fish populations have disappeared or been reduced
• Tidal wetlands have been reduced by 92%
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CALFED Bay-Delta Program
• The CALFED program was established to develop
and implement a plan to restore ecological health
and improve water management
• The program is not working
• Farmers, government agencies, and environmental
groups do not agree with scientists’
recommendations
• Other estuaries around the world are suffering
• The Aswan Dam on the Nile River prevents the
Mediterranean Sea from being flushed
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Floods
• Dams help prevent devastating floods
• Many areas have increased flood frequency and
severity
• Erosion and reduced infiltration from deforestation
and cultivation
• “Sponge effects” of forests helps prevent floods
• Deforestation in the Himalayan foothills causes
extreme flooding in Bangladesh
• India’s Koshi River broke through dirt levees
• Caused massive floods and stranded a million people
• The breach came because of massive silt deposition
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Flooding of the Koshi River
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Groundwater levels
• The Ogallala aquifer supplies irrigation water to 4.2
million hectares (10.4 million acres) in seven U.S.
states
• 20% of the irrigated land in the U.S.
• It has “fossil water” recharged during the last ice age
• Water is being withdrawn twice as fast as it
recharges
• Water tables in the Ogallala aquifer have dropped
30–60 m (100–200 ft)
• Irrigated farming has stopped in some areas
• Within 20 years, 1.2 million hectares (3 million acres)
will be abandoned or converted to dryland farming
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Some aquifers are nonrenewable
• Nonrenewable groundwater: more than 75% of
aquifers have recharge rates of centuries
• Renewable groundwater is replenished by
percolation
• Is vulnerable to variations in precipitation
• We are tapping large, but not unlimited, natural
reservoirs
• Sustainability depends on balancing withdrawal
rates with recharge rates
• Most groundwater in arid regions has no recharge
• It must be considered nonrenewable, like oil
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Exploitation of an aquifer
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Impacts of falling water tables
• The simplest indication that groundwater
withdrawals exceed recharge rates
• Falling water tables
• Common throughout the world
• Decreased crop production
• Diminishing surface water
• Dries up wetlands, springs and seeps, streams,
rivers
• Excessive groundwater removal creates the same
results as diverting surface water
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Land subsidence
• Groundwater fills spaces in the ground
• Helping support overlying rock and soil
• Dropping water tables removes this support
• Land subsidence: gradual settling of the land
• Land may sink 10–15 cm (6–12 in.) per year
• Causes building foundations, roadways, and pipes
to crack
• Results in flooding in coastal areas
• People in developing areas drill their own wells
• Causing subsidence—a case of tragedy of the
commons
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Falling water tables: sinkholes
• A sinkhole: another kind of land subsidence
• Results when an underground cavern is drained of its
supporting groundwater and suddenly collapses
• Sinkholes can be 91 m (300 ft.) across and 150 feet
deep
• They are particularly severe in the southeastern
U.S.
• 4,000 sinkholes have formed in Alabama alone
• They have “consumed” buildings, livestock, sections
of highways
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Sinkhole
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Saltwater intrusion
• In many coastal areas, springs of outflowing
groundwater lie under the ocean
• High water tables keep pressure in the aquifer
• Fresh water flows into the ocean
• Wells near the ocean yield fresh water
• Lowering the water table reduces pressure,
allowing salt water to flow into the aquifer and wells
• This is a serious problem in many European
countries along the Mediterranean coast
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Saltwater intrusion
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Water stewardship: supply and
public policy
• The water cycle can meet human needs for fresh water
• But water is often not located where it is most needed,
resulting in persistent water scarcity
• The developing world lacks infrastructure (wells, watertreatment systems, dams) to capture and distribute
water
• Increasing populations create increasing water demand
• Water for agriculture dominates demand
• To eradicate hunger, water use will have to double
• An unacceptable and impossible scenario
• Only five possibilities exist to meet future water needs
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Capture more runoff water
• 260 new dams become operational each year
• Down from 1,000/yr
• China’s Three Gorges Dam was constructed across
the Yangtze River
• The centerpiece of the government’s efforts to
industrialize
• The largest hydroelectric project in the world
• 1.2 million people have been relocated to make way
for the 600 km (370 mile) long reservoir
• 3–4 million more will be displaced
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Three Gorges Dam
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Impacts of the Three Gorges Dam
• Yangtze River flow has been reduced 50%
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Salt water is creeping upriver
Ships have been stranded
Pollutants have accumulated
Fish populations have been reduced
The dam may be breached by earthquakes
Chinese officials stifled internal criticism
• The dam will provide renewable energy and control
floods
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Wild rivers
• The 1968 Wild and Scenic Rivers Act protects
some rivers
• It prevents them from being dammed or affected by
harmful operations
• 11,300 miles of rivers have been protected
• 60,000 more miles qualify for protection
• Compared to the 600,000 miles that have been
dammed
• Wild and scenic rivers are equivalent to national
parks
• They need public supporters and defenders
• Special interests (hydropower industry, agriculture)
try to undo recent work establishing wild and scenic
rivers
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Tapping more groundwater
• Groundwater depletion: the greatest threat to
irrigated agriculture
• Declining water tables occur in India, China,
American West, the former Soviet Union, the
Arabian Peninsula
• A 20% expansion in irrigation may be possible
• But will not meet food needs by 2030
• Groundwater is also being polluted by fertilizers,
pesticides, animal waste, and industrial chemicals
• Arsenic in groundwater in India and Bangladesh has
sickened and killed millions
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Desalting seawater
• Oceans are an inexhaustible source of water
• Desalination: desalting of seawater for domestic use
• 13,000 desalination plants in 120 countries
• Especially in the Middle East
• Smaller plants use microfiltration (reverse osmosis [RO])
• Water is forced through a fine membrane to remove salt
• Large plants use distillation (evaporation and
condensation)
• Waste heat from power plants may be used
• Desalination costs two to four times what most U.S.
people pay
• Desalinized water costs about $2 for 1,000 gallons
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Tampa Bay leads the way in the U.S.
• The Tampa Bay seawater desalination plant was
completed in 2008
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The first U.S. plant built for a primary water source
It uses salty cooling water from a power plant
It produces 25 million gallons per day (MGD)
It costs $2.50/1,000 gallons (groundwater = $1/1,000
gallons)
• Most people in the U.S. can afford desalinized water
• But costs are too high for most agricultural use
• The world’s largest plant is in the United Arab
Emirates
• It produces 215 MGD (2,500 gallons/second)
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Desalination plant
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Using less water
• People in developing nations use 1 gallon/person/day
for all their needs, including cooking and washing
• A person in the U.S. uses 380 liters (100 gal) per day
• Indirect uses (irrigation) increases use to 4,900 liters
(1,000 gal) per person per day
• Don’t think how much water we need and where we
get it
• Think how much water is available and how can we
best use it
• The rate of water use has dropped because of
conservation
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Conserving water: agriculture
• Agriculture is the largest user of fresh water
• 40% of crops are grown in irrigated soil
• Current flood or center-pivot irrigation wastes huge
amounts of water
• Evaporation, percolation, runoff
• The surge flow method uses computers to control
release of water
• The drip irrigation method uses pipes with holes to
drip water at the base of each plant
• Wastes less water, retards salinization, increases
yields
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Drip irrigation
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Why don’t farmers switch to drip
irrigation?
• 99% of world irrigation is still by traditional flood or
center-pivot methods
• It is cheaper to use traditional methods than switch
• The U.S. government pays $400/acre in subsidies
• But collects only 10% of the costs in water fees
• Farmers pay almost nothing for water
• It makes financial sense to use the cheapest (but
most wasteful) system
• Reducing subsidies would encourage water
conservation through using more efficient irrigation
technologies
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Treadle pumps
• Rural poor in developing countries cannot afford
irrigation
• Low-cost treadle pumps allow farmers to irrigate
fields
• Cost less than $35 per system
• The treadle works like a step exercise machine
• It is locally manufactured
• It has been adopted by millions
• Farmers can irrigate small plots during dry seasons
• Over 1.5 million pumps in Bangladesh have
increased productivity of 600,000 acres of farmland
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Treadle pump
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Municipal systems
• Each person in a modern home uses 100
gallons/day
• Mostly for washing and removing wastes (flushing
toilets, taking showers, doing laundry)
• Conservation has been presented as “save the
environment”
• This does not work
• It will be expensive and impossible to get more
water through traditional reservoirs and wells
• The only practical alternative is to save water
• Cities provide free faucet repair and low-flow showers
• Xeriscaping: planting plants that don’t require
watering
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A flush world
• In 1997 it became illegal to sell 6-gallon commodes
• New toilets use 1.6 gallons or even less water
• 50 million U.S. low-flow toilets save 600 million
gallons/day
• It is wasteful to use high-quality water to water
lawns or flush toilets
• Gray water: slightly dirtied water from sinks,
showers, tubs, and laundry tubs
• Used in toilets, watering lawns, washing cars
• Some treated water is higher quality than river and
lake water
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A WaterSense commode
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Making food production more efficient
• Most agriculture in developing countries is rain-fed
• With dryland soils, crops have low yields
• Water harvesting methods improve yields
• For example, storing rainfall with “check dams”
• Conservation tillage enhances rainfall retention and
soil fertility and decreases erosion
• Wasting food also wastes water
• Countries that import food (ship virtual water) save
water
• But many nations are too poor to buy food
• There is still a gap between food production and
need
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Public policy challenges
• Humans use 25% of total terrestrial evaporation
• 56% of accessible precipitation runoff
• Many facets of water use are unsustainable
• Public policy must strike a balance between water
needs
• Water wars: conflicts between using water for
drinking and using it for agriculture
• In southern California, irrigation water is being
diverted to San Diego
• The Salton Sea is shrinking, spreading salt,
decreasing wildlife habitat, and destroying the
fishery
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National water policy
• The U.S. has not addressed water resources and
needs with a national policy
• The Clean Water Act authorizes the Environmental
Protection Agency (EPA) to oversee water quality
• But not quantity
• Most water policy decisions are made at the local
and regional levels
• The last water policy report was in 1950
• The U.S. needs a water policy to collect data on
water resources and problems and issue
recommendations
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Key issues in water policy
• Water efficiency must be the primary strategy for
meeting future needs
• Water subsidies must be reduced or eliminated
• Polluters must be charged according to their
effluents
• Watershed management must be integrated into
water pricing
• Dams must be operated to maintain river flow that
simulates natural flow regimes
• The U.S. must provide international development
aid
• Much more research and monitoring is needed
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International action
• The World Commission on Water for the 21st
Century sponsors the World Water Forum
• The forum’s findings relate to solving water problems
• Especially in the developing world
• The problem is not too little water
• We have not learned how to manage Earth’s water
• “There is a water crisis…of bad institutions, bad
governance, bad incentives and bad resource
allocation”
• We can continue with business as usual
• Or we can move from vision to action
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CHAPTER 10
Water: Hydrologic
Cycle and Human Use
Active Lecture Questions
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Review Question-1
True or False: Fresh water is a continually
renewable resource.
a. True
b. False
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Review Question-1 Answer
True or False: Fresh water is a continually
renewable resource.
a. True
b. False
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Review Question-2
Water enters the atmosphere through ______
and ______ and returns to land and oceans
through ______ and ______.
a. evaporation; transpiration; condensation;
precipitation
b. condensation; precipitation; evaporation;
transpiration
c. evaporation; condensation; transpiration;
precipitation
d. evaporation; precipitation; condensation;
transpiration
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Review Question-2 Answer
Water enters the atmosphere through ______
and ______ and returns to land and oceans
through ______ and ______.
a. evaporation; transpiration; condensation;
precipitation
b. condensation; precipitation; evaporation;
transpiration
c. evaporation; condensation; transpiration;
precipitation
d. evaporation; precipitation; condensation;
transpiration
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Review Question-3
______ occurs when water is separated from
the solutes and particles it contains.
a.
b.
c.
d.
Precipitation
Water vapor
Purification
Cloud formation
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Review Question-3 Answer
______ occurs when water is separated from
the solutes and particles it contains.
a.
b.
c.
d.
Precipitation
Water vapor
Purification
Cloud formation
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Review Question-4
Wells for withdrawing groundwater must be dug
______ the water table.
a. above
b. below
c. at the level of
d. around the perimeter of
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Review Question-4 Answer
Wells for withdrawing groundwater must be dug
______ the water table.
a. above
b. below
c. at the level of
d. around the perimeter of
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Review Question-5
All of the following are ecological impacts of
dams except
a. valuable habitats are lost.
b. waterways below the dam are deprived
of water.
c. wetlands are recharged with water
constantly.
d. animals that depend on the water are
adversely affected.
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Review Question-5 Answer
All of the following are ecological impacts of
dams except
a. valuable habitats are lost.
b. waterways below the dam are deprived
of water.
c. wetlands are recharged with water
constantly.
d. animals that depend on the water are
adversely affected.
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Interpreting Graphs and Data-1
Most of northern Africa receives ______ inches
of precipitation each year.
a.
b.
c.
d.
80 and over
50-99
under 25
under 10
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Interpreting Graphs and Data-1 Answer
Most of northern Africa receives ______ inches
of precipitation each year.
a.
b.
c.
d.
80 and over
50-99
under 25
under 10
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Interpreting Graphs and Data-2
The number one use for water worldwide is
a.
b.
c.
d.
domestic.
industry.
agriculture.
zoos.
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Interpreting Graphs and Data-2 Answer
The number one use for water worldwide is
a.
b.
c.
d.
domestic.
industry.
agriculture.
zoos.
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Thinking Environmentally-1
______ water is water in vapor form, while
______ water is liquid water wherever it occurs.
a.
b.
c.
d.
Blue; green
Gray; blue
Green; gray
Green; blue
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Thinking Environmentally-1 Answer
______ water is water in vapor form, while
______ water is liquid water wherever it occurs.
a.
b.
c.
d.
Blue; green
Gray; blue
Green; gray
Green; blue
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Thinking Environmentally-2
Atmospheric pollution (in the form of
anthropogenic aerosols) affects the hydrologic
cycle in which of the following ways?
a. The aerosols suppress rainfall.
b. The aerosols have a cooling effect in the
atmosphere.
c. The aerosols lead to increased dust and
smoke in the air.
d. all of the above
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Thinking Environmentally-2 Answer
Atmospheric pollution (in the form of
anthropogenic aerosols) affects the hydrologic
cycle in which of the following ways?
a. The aerosols suppress rainfall.
b. The aerosols have a cooling effect in the
atmosphere.
c. The aerosols lead to increased dust and
smoke in the air.
d. all of the above
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