Geography Reference
In-Depth Information
Field Note
“We drove north on Route 89 from Tucson, Arizona, across
the desert. Drought rules the countryside here, and dams
conserve what water there is. Snaking through the landscape
are lifelines such as this, linking Coolidge Dam to distant
farms and towns. In the vast, arid landscape, this narrow rib-
bon of water seems little more than an artifi cial brook—but
to hundreds of thousands of people, this is what makes life
possible in the Southwest.”
Figure 13.8
Tucson, Arizona.
© H. J. de Blij.
of precipitation, with the largest totals recorded in equa-
torial and tropical areas of Southeast Asia, South Asia,
central and coastal West Africa, and Middle and South
America. The volume of precipitation in the world as
a whole is enormous; spread out evenly, it would cover
the land area of the planet with about 83 centimeters
(33 inches) of water each year. Much of that water is lost
through runoff and evaporation, but enough of it seeps
downward into porous, water-holding rocks called
aqui-
fers
to provide millions of wells with steady fl ows. In the
United States alone, it is estimated that there is 50 times
as much water stored in aquifers as there is precipitation
falling on the land surface every year.
Despite such favorable data, the supply of water is
anything but plentiful (Fig. 13.8). Chronic water short-
ages affl ict tens of millions of farmers in Africa and hun-
dreds of thousands of city dwellers in Southern California;
water rationing has been imposed in rainy South Florida
and in Spain, which faces the Mediterranean Sea.
In many areas of the world, people have congre-
gated in places where water supplies are insuffi cient,
undependable, or both. In California, people are some-
times not allowed to wash their cars or refi ll their swim-
ming pools; these are minor inconveniences compared
to the fate faced by millions of Sudanese trying to escape
their country's civil war by fl eeing to parched pans of the
Sahara. In Florida, where the urban population depends
on the Biscayne Aquifer for most of its water, the long-
term prospect is troubled: whenever seasonal rainfalls do
not reach their projected averages, Floridians overuse the
Biscayne Aquifer, and saltwater enters the aquifer from
the nearby Atlantic Ocean. The invasion of saltwater over
time can permanently destroy a fresh water aquifer.
Hundreds of millions of people still cluster along
several of Earth's great rivers. Indeed, nearly three-
quarters of all the fresh water used annually is consumed
in farming, not in cities. In California, where about 80 per-
cent of available water is used for irrigation, this has led to
an intense debate: should cities be provided with ample
water at the expense of Central Valley farms, and should
fruits and vegetables be bought from elsewhere, even
overseas, rather than be grown locally?
Industries use another 20 percent of the world's
water supply, contributing heavily to pollution when the
used water is returned to streams, lakes, and aquifers.
When communist rule ended in eastern Europe, tests
indicated that the region's rivers and groundwater were
among the most severely polluted in the world because
industries there had not been adequately regulated.
As human populations have expanded, people have
increasingly settled in arid regions. One of the great
ecological disasters of the twentieth century occurred in
Kazakhstan and Uzbekistan, whose common boundary
runs through the Aral Sea. Streams that fed this large body
of water were diverted to irrigate the surrounding desert,
mainly for commercial cotton production. Heavy use of
chemical pesticide ruined the groundwater below, caus-
ing a health crisis that some observers describe as an “eco-
logical Chernobyl” (referring to the 1986 nuclear reactor
meltdown in the Ukraine). In the meantime the Aral Sea
began to dry up, and by the mid-1990s it had lost more
than three-quarters of its total surface area (Fig. 13.9).
School children are not typically taught to think
about the geography of water—how varying precipita-
tion and human uses of water affect its availability and
quantity. Textbooks teach that water is a constant whose
