Healthy soil and sustainable growing

["Tradingpost" <tradingpost@lobo.net>]

I've been mentioning water issues before but it's not a glamorous subject 
apparently.
paul tradingpost@lobo.net
~~~~~~~~~~~~~~~~~~~~~

Groundwater Depletion Raises Likelihood of Global Food Crises
September 27, 2010
http://blogs.nationalgeographic.com/blogs/news/chiefeditor/2010/09/groundwater-depletion-food-crisis.html

Water budgets are badly out of balance, throwing many regions into water debt.
The water depleted annually could feed 940 million people for a year.

By Sandra L. Postel, National Geographic Freshwater Fellow

This post is part of National Geographic's Freshwater Initiative.

Out of sight, out of mind means deep trouble when it comes to the reserves of 
freshwater stored underground. New numbers are out on the rate of groundwater 
depletion around the globe, and if they hold up to further scrutiny, the 
world is almost certainly facing a future of food shortages.

In an upcoming issue of Geophysical Research Letters, a journal of the 
American Geophysical Union, Professor Marc Bierkens of Utrecht University in 
the Netherlands and his colleagues estimate that the rate at which humanity 
is pumping dry the underground reservoirs that hundreds of millions of people 
depend upon for food and drinking water more than doubled between 1960 and 
2000.

groundwater.jpgGlobal map of groundwater depletion, measured in millimeters 
of water per year, courtesy of American Geophysical Union.

Using global groundwater data and hydrologic modeling to calculate the 
volumes of water added to and withdrawn from underground aquifers, the 
researchers estimate that groundwater depletion rose from 33 trilliongallons 
(126 billion cubic meters) per year in 1960 to 75 trillion gallons (283 
billion cubic meters) per year in 2000. The rate increased more or less 
linearly from 1960 up to the early 1990's, but then climbed sharply--likely 
due to escalating groundwater use in China and India.

Although the research team doesn't delve into the implications of their 
findings, a lot is at stake--especially for the world's food supply. 
Irrigation, which accounts for 70 percent of world water use, is the 
principal cause of the groundwater depletion. About 40 percent of the world's 
food supply comes from the 18 percent of farmland that's irrigated, making 
irrigated farming a cornerstone of global food security. But in recent 
decades as more farmers have turned from rivers to groundwater for their 
water supply, groundwater pumping in many areas has become unsustainable.

Just as a bank account shrinks when withdrawals exceed deposits, so does a 
groundwater account. Water budgets are badly out of balance, throwing many 
regions into water debt. In effect, farmers are using some of tomorrow's 
water to meet today's food demands.

(Related: "How to Stem a Global Food Crisis? Store More Water" and "365 
Trillion Gallons of Water Thrown Away With Our Food Every Year.")

It takes approximately 396,300 gallons (1,500 cubic meters) of water to 
produce one ton of grain. (That's an approximate average based on the water 
needed to produce rice, wheat and corn.) So the estimated 75 trillion gallons 
(283 billion cubic meters) of groundwater depleted in 2000 is sufficient to 
produce 188.6 million tons of grain. That's enough to feed 943 million people 
a subsistence diet for a year.

The highest rates of water loss are occurring in critical regions of 
irrigated farming--including the north plain of China, northwestern India, 
and the central valley of California. In most areas groundwater is not 
monitored or regulated, so as increasing numbers of wells extract ever more 
water, the "tragedy of the commons" is playing out on a large scale.

A little over a decade ago, I took a stab at estimating groundwater depletion 
using national-level data for China, India, the United States, North Africa 
and Saudi Arabia. For these regions, I came up with a net loss of 43 trillion 
gallons (164 billion cubic meters) a year. Adding in a ballpark estimate that 
inclusion of the rest of the world would bump this figure up by 25 percent, I 
arrived at a global depletion rate of 53 trillion gallons (200 billion cubic 
meters) per year--not too far off from the 283 billion figure of this current 
study, which may lend a little confidence to both.

This global assessment comes on the heels of regional studies that also 
corroborate the severity of the groundwater depletion problem. Using new 
satellite technology called GRACE - the Gravity Recovery & Climate Experiment 
- scientists with the University of California at Irvine and the National 
Atmospheric and Space Administration have estimated that California's Central 
Valley - the fruit and vegetable bowl for the nation - has lost a volume of 
groundwater equivalent to about two-thirds the volume of Lake Mead. 
Scientists with the U.S. Geological Survey have estimated that as of 2005, a 
volume of water equivalent to two-thirds of Lake Erie had been depleted from 
the Ogallala Aquifer, which supplies 30 percent of the groundwater used for 
U.S. irrigation. And in a 2009 study in Nature, again using the GRACE 
technology, scientists estimated that northern India, which encompasses that 
nation's breadbasket, is losing groundwater at a rate of 54 billion cubic 
meters per year, placing the livelihoods of 114 million people in that region 
at risk.

(Read "NASA Satellites Track Vanishing Groundwater" in National Geographic 
News.)

With modern satellite capabilities and new modeling and monitoring 
techniques, it is now possible to know what is happening to our water 
supplies underground. The picture is not good. The challenge now is to 
encourage the adoption of more efficient irrigation systems, more appropriate 
cropping patterns, and other measures to bring the world's groundwater 
accounts into balance. The future food security of hundreds of millions of 
people depends on this.
~~~~~
Sandra Postel directs the independent Global Water Policy Project and 
lectures, writes, and consults on international water issues. She is also 
Freshwater Fellow of the National Geographic Society, and serves as lead 
water expert for the Society's freshwater initiative.

Sandra is the author of several acclaimed books, including Pillar of Sand: 
Can the Irrigation Miracle Last? (W.W. Norton, 1999) and Last Oasis (W.W. 
Norton, 1997), which appears in eight languages and was the basis for a 1997 
PBS documentary. She is also co-author, with Brian Richter, of Rivers for 
Life. Her essay "Troubled Waters" was selected for Best American Science and 
Nature Writing. She is a 1995 Pew Scholar in Conservation and the Environment.