Groundwater depletion is detected from space

[Barrett808]

IRVINE, Calif. — Scientists have been using small variations in the Earth’s gravity to identify trouble spots around the globe where people are making unsustainable demands on groundwater, one of the planet’s main sources of fresh water.

They found problems in places as disparate as North Africa, northern India, northeastern China and the Sacramento-San Joaquin Valley in California, heartland of that state’s $30 billion agricultural industry.

Jay S. Famiglietti, director of the University of California’s Center for Hydrologic Modeling here, said the center’s Gravity Recovery and Climate Experiment, known as Grace, relies on the interplay of two nine-year-old twin satellites that monitor each other while orbiting the Earth, thereby producing some of the most precise data ever on the planet’s gravitational variations. The results are redefining the field of hydrology, which itself has grown more critical as climate change and population growth draw down the world’s fresh water supplies.

Grace sees “all of the change in ice, all of the change in snow and water storage, all of the surface water, all of the soil moisture, all of the groundwater,” Dr. Famiglietti explained. ...

Groundwater depletion is detected from space

[Ghost Dog]

1. That's a useful monitoring tool.

http://www.ess.uci.edu/~hydrogroup/iresearch.html

As the lead spacecraft passes over a patch of anomalously strong gravity, it accelerates ahead of the trailing spacecraft. Once past the anomaly, the lead satellite slows back down. Then the trailing spacecraft accelerates and again closes on the leader. By making repeated passes over the same spot, GRACE measures changes in Earth's gravity, which are mainly due to water moving on and under the surface. Most famously, GRACE has recorded the shrinking of ice sheets; it has also detected shifting ocean currents, the desiccation of droughts, and the draining of large lakes.

Outside of wasting ice sheets, the world's largest broad-scale decline in gravity during GRACE's first 6 years came across a 2.7-million-square-kilometer, east-west swath centered on New Delhi. That's according to a study in press in Geophysical Research Letters by geophysicists Virendra Tiwari of the National Geophysical Research Institute in Hyderabad, India; John Wahr of the University of Colorado, Boulder; and Sean Swenson of the National Center for Atmospheric Research in Boulder. Adjusted for natural variations due to changing precipitation and evaporation, the decline in gravity that GRACE determined equates to a net loss of 54 plus or minus 9 cubic kilometers of groundwater per year, the group reports. That would produce a fall in the water table of about 10 centimeters per year averaged over the entire region.

A falling water table across the northern Indian subcontinent comes as no great surprise. The GRACE region of sharp groundwater depletion coincides with the world's most intensely irrigated land: Fifty percent to more than 75% of the land is equipped for irrigation with pumped groundwater or reservoir water. And then there are those 600 million people drawing heavily on groundwater. But, the group calculates, the GRACE-determined depletion rate implies that groundwater was being pumped out 70% faster in this decade than the Central Ground Water Board of India estimated it was in the mid-1990s. The apparent surge in withdrawal would have been large enough to turn a once-stable water table into a falling one that demands ever-deeper wells and bigger pumps and may draw in salty or polluted water.

GRACE "has shown us we can do a pretty reasonable job from space" gauging groundwater depletion, says Famiglietti. "We can help regional water managers by giving them a holistic view of a whole system." Still, across the subcontinent, no one knows how far down the water goes. They just know, as Famiglietti notes, that "it's not bottomless."

/... http://news.sciencemag.org/sciencenow/2009/08/10-01.html

+ Good video here: http://www.nature.com/nature/videoarchive/indianhotspot/

[opihimoimoi]

2. this should be recd and k'd :o)

[Viva_La_Revolution]

3. ok nt

[NYC_SKP]

4. Note the max change in this California map, drop of 11 feet, per YEAR!

Yikes!