WheatSorghumCornCourtesy NASA}ÀVÕÌÕÀ>ÊÕÃiÊvÊÜ>ÌiÀÊUÊ}ÕÀiÊ£ä°ÇÊ
These fields in Kansas use center-pivot irrigation, which minimizes evaporative water loss
and gives fields a distinctive circular shape. Each circle is the result of a long irrigation pipe
that extends along the radius from the circle’s center to its edge and slowly rotates,
spraying the crops. This satellite photo, taken in June, shows wheat fields (bright yellow),
corn fields (dark green), and newly emerging sorghum (light green).
Aquifer Depletion
Aquifer depletion from excessive removal of groundwa-
ter lowers the water table, the upper surface of the satu-
rated zone of groundwater (see Figure 10.4). Prolonged
aquifer depletion drains an aquifer dry, effectively elimi-
nating it as a water resource. Even areas with high rainfall
can experience aquifer depletion if humans
remove more groundwater than can be re-
charged. In addition, aquifer depletion from
porous sediments causes subsidence, or sink-
ing, of the land above it. Saltwater intrusion
occurs along coastal areas when groundwater
is depleted faster than it recharges. Saltwater
intrusion is also occurring in low-lying areas
due to sea-level rise associated with global cli-
mate change. Well water in such areas eventu-
ally becomes too salty for human consumption
or other freshwater uses.lands has become increasingly important worldwide in
efforts to produce enough food for burgeoning popula-
tions (}ÕÀiÊ£ä°Ç). Since 1955, the amount of irrigated
land has more than tripled; Asia has more agricultural
land under irrigation than do other continents, primar-
ily in China, India, and Pakistan. Water use for irrigation
will probably continue to increase in the 21st
century, but at a slower rate than in the last
half of the 20th century.
Population growth in arid and semiarid
regions intensifies water shortage. More
people need food, so additional water re-
sources are diverted for irrigation. Also, the
immediate need for food prompts people to
remove natural plant cover to grow crops on
marginal lands subject to frequent drought,
which in turn reduces water absorption into
soils when rains do come.
aquifer depletion
The removal of
groundwater
faster than it can
be recharged by
precipitation or
melting snow.
saltwater
intrusion The
movement of
seawater into a
freshwater aquifer
near the coast.