Agriculture Dominates Freshwater Use in the U.S.
Noel
Gollehon
Irrigation made the desert bloom in the West
and improved crop alternatives in the East. The
less than 20 percent of cropland that is irrigated
produces almost half of all crop sales. But this
intensive, high-yielding agriculture takes many
inputs—fertilizer, chemicals, management,
and, especially, water.
Agriculture accounted for over
80 percent of the Nation’s consumptive water
use over 1960-95—greater than any other sector,
both in total and as a share of water withdrawn.
Water use can be measured in terms of withdrawals
(total water withdrawn from the environment) or
consumptive use—the difference between withdrawals
and the amount of water returned through return
flows and runoff. While the thermoelectric sector
withdraws almost as much freshwater as agriculture
(152 versus 159 million acre-feet in 2000), most
water diverted to cool thermoelectric power plants
is returned to lakes, rivers, and streams. On the
other hand, most agricultural water use is for irrigation,
and that water is mostly taken up by crops, with
relatively little returning to the immediate water
environment (streams and aquifers) for reuse.
 |
Most agricultural water withdrawals
occur in the arid Western States where irrigated
production is concentrated. In 2000, about 85 percent
of total agricultural withdrawals occurred in a
19-State area encompassing the Plains, Mountain,
and Pacific regions. In the Mountain region, over
90 percent of the water withdrawn is used by agriculture,
almost all (96 percent) for irrigation. Nationally,
irrigation is the dominant agricultural water use,
but water withdrawn for livestock and aquaculture
production (including fish hatcheries) accounts
for almost 20 percent of withdrawals in the North-Central
and Eastern States. Even in these more humid States,
irrigation is the dominant agricultural water use.
Whether water is returned to streams
and aquifers or not, water losses, runoff, return
flows, and groundwater recharge can have varying
effects on the environment. For example, water that
is diverted for cooling purposes is typically returned
at a higher temperature, which may harm the environment.
Environmental impacts can occur from surface-water
withdrawals that reduce streamflow. In areas where
streamflow is limited, it is usually also needed
for riparian systems, fish habitat, groundwater
recharge, wetlands preservation, and other extractive
uses. When groundwater withdrawals exceed natural
rates of aquifer recharge, environmental consequences
of groundwater extraction can include land subsidence
and reduced flow from natural springs, which reduces
surface-water availability.
|
Download PDF version