Page 417 - Environment: The Science Behind the Stories

Figure 15.11 Ships
were stranded along the
former shoreline of the
Aral Sea because the
waters receded so far and
so quickly. Today restora-
tion efforts are beginning to
reverse the decline in the
northern portion of the sea,
and waters there are slowly
rising. (a) 16th-century chapel in Mexico City (b) Sinkhole in Florida

the land with water from the two rivers that supplied the Aral Groundwater can also be depleted
Sea its water. For a few decades this boosted Soviet cotton
production, but it shrunk the Aral Sea, and the irrigated soil Groundwater is more easily depleted than surface water
became salty and waterlogged. Today 60,000 fishing jobs are because most aquifers recharge very slowly. If we compare an
gone, winds blow pesticide-laden dust up from the dry lake- aquifer to a bank account, we are making more withdrawals
bed (Figure 15.11), and little cotton grows on the blighted soil. than deposits, and the balance is shrinking. Today we are min-
3
3
However, all may not be lost: Scientists, engineers, and local ing groundwater, extracting 160 km (5.65 trillion ft ) more
people struggling to save the northern portion of the Aral Sea water each year than returns to the ground. This is a problem
and its ecosystems may now have begun reversing its decline. because one-third of Earth’s human population—including
Worldwide, roughly 15–35% of water withdrawals for 99% of the rural population of the United States—relies on
irrigation are thought to be unsustainable. In areas where agri- groundwater to meet its needs for water.
culture is demanding more fresh water than can be sustainably As aquifers are mined, water tables drop. Groundwater
supplied, water mining—withdrawing water faster than it can becomes more difficult and expensive to extract, and eventu-
be replenished—is taking place (Figure 15.12). In these areas, ally it may be depleted. In parts of Mexico, India, China, and
aquifers are being depleted or surface water is being piped in many Asian and Middle Eastern nations, water tables are fall-
from other regions. ing 1–3 m (3–10 ft) per year. In the United States, by the late

High overuse Adequate supply
Moderate overuse Little or no use
Low overuse
Figure 15.12 Irrigation for agriculture is the main contributor to unsustainable water use. Mapped are
regions where overall use of fresh water (for agriculture, industry, and domestic use) exceeds the available sup-
ply, requiring groundwater depletion or diversion of water from other regions. The map understates the problem,
because it does not reflect seasonal shortages. Data from UNESCO, 2006. Water: A shared responsibility. World Water
416 Development Report 2. UNESCO and Berghahn Books.

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