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  • From: "Tradingpost" <tradingpost@lobo.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] Has the U.S. Passed the Point of Peak Water?
  • Date: Tue, 12 Oct 2010 11:05:39 -0600


Has the U.S. Passed the Point of Peak Water?
http://www.commondreams.org/view/2010/10/12-5
by Peter H. Gleick Tuesday, October 12, 2010

Freshwater is fundamental for maintaining human health, agricultural
production, economic activity, and critical ecosystem functions. But as
populations and economies grow, new constraints on water resources are
appearing, raising questions about ultimate limits to water availability.
Such resource questions are not new. The specter of "peak oil" -- a peaking
and then decline in oil production -- has long been predicted and debated. A
recent paper in the Proceedings of the National Academy of Sciences I wrote
with a colleague, Meena Palaniappan, offers three concepts of "peak water:"
peak renewable water, peak nonrenewable water, and peak ecological water. And
it looks like the U.S. has passed all three points.

Peak renewable water applies where flow constraints limit total water
availability over time. Peak nonrenewable water is observable in groundwater
systems where production rates substantially exceed natural recharge rates
and where overpumping or contamination leads to a peak of production followed
by a decline, similar to more traditional peak-oil curves. Peak "ecological"
water is defined as the point beyond which the total costs of ecological
disruptions and damages exceed the total value provided by human use of that
water.

Peak Renewable Water. A significant fraction of total human use of water
comes from water taken from renewable flows of rainfall, rivers, streams, and
groundwater basins that are recharged over relatively short time frames.
Because a particular water source may be renewable, however, does not mean
that it is unlimited. Indeed, the first peak water constraint is the limit on
total water that can be withdrawn from a system. The ultimate limit is the
complete renewable flow.

When human demands for water from a watershed reach 100 percent of renewable
supply, we can't take any more, and we've reached "peak renewable" limits.
Indeed, problems begin to arise long before demands reach 100 percent of
renewable supplies. For a number of major river basins, peak renewable water
limits have already been reached. The Colorado River in the United States,
for example, is shared by seven US states and Mexico, and in an average all
the parties take all the water. Other rivers are increasingly reaching their
peak limits as well, including the Huang He (Yellow River) in China, the Nile
in Northern Africa, and the Jordan in the Middle East, where river flows now
often fall to zero before they reach their ends.

Peak Nonrenewable Water. In some watersheds, water comes from stocks of water
that are effectively nonrenewable, such as groundwater aquifers with very
slow recharge rates or groundwater systems damaged by compaction or other
physical changes in the basin. When the use of water from a groundwater
aquifer far exceeds the natural recharge rate, this stock of groundwater will
be quickly depleted. Or when groundwater aquifers become contaminated with
pollutants that make the water unusable, a renewable aquifer can become
nonrenewable, very much like oil fields. Continued production of water beyond
natural recharge rates will become increasingly difficult and expensive as
groundwater levels drop, leading to a peak of production, followed by
diminishing withdrawals and use. This kind of unsustainable groundwater use
can be found in the Ogallala Aquifer in the Great Plains of the United
States, the North China plains, California's Central Valley, and numerous
basins in India. In these basins, extraction may not fall to zero, but
current rates of pumping cannot be maintained.

Peak Ecological Water. For many watersheds, a more immediate and serious
concern than running out of water is exceeding a point of water use that
causes serious or irreversible ecological damage. Not only does water sustain
human life and commercial and industrial activity, but it is also fundamental
for animals, plants, habitats, and environmentally dependent livelihoods.
Each new incremental supply project that captures water for human use and
consumption decreases the availability of that source to support ecosystems
and diminishes the capacity to provide services. The water that has been
temporarily appropriated or moved was once sustaining habitats and
terrestrial, avian, and aquatic plants and animals. By some estimates, humans
already appropriate almost 50 percent of all renewable and accessible
freshwater flows, leading to significant ecological disruptions. Since 1900,
half of the world's wetlands have disappeared. The number of freshwater
species has decreased by 50% since 1970, faster than the decline of species
on land or in the sea.

The term "peak ecological" water refers to the point where taking more water
for human use leads to ecological disruptions greater than the value that
this increased water provides to humans. Economists have long noted the
difficulty of quantifying this point because of problems in assigning
appropriate valuations to each unit of water or each unit of ecosystem
benefit in any watershed, but the mistaken assumption that such values are
zero has led to them being highly discounted, underappreciated, or ignored in
20th century water policy decisions.

There is strong evidence that the United States may have already passed the
points of peak water, including peak renewable, nonrenewable, and ecological
water, in many watersheds, especially (but not exclusively) in the more arid
west. Indeed, when we look at data on total water withdrawals and use in the
US (see the Figure, which shows total US water withdrawals and total US GNP
over the past century), it shows that maximum water use occurred more than 30
years ago, and that we are now using less water overall, and much less water
per person, than in 1980. The bad news is that this suggests we have reached,
or passed the point of peak water -- as is increasingly obvious in the
regions I've mentioned above. The good news, however, is that we have been
able to continue to grow our economy and meet the demands of growing
populations, with less and less water, through smart technology, regulations,
education, and water conservation and efficiency programs. I think we're in a
transition to a new way of thinking about and managing our water. And the
sooner the better.




  • [Livingontheland] Has the U.S. Passed the Point of Peak Water?, Tradingpost, 10/12/2010

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