Severe drought is causing the western US to rise

August 21, 2014
Plate Boundary Observatory GPS station P298, located near Coalinga, California. Surface displacement data from P298 was included in the determination of water loading changes in the western United States. Credit: Andre Basset, UNAVCO

The severe drought gripping the western United States in recent years is changing the landscape well beyond localized effects of water restrictions and browning lawns. Scientists at Scripps Institution of Oceanography at UC San Diego have now discovered that the growing, broad-scale loss of water is causing the entire western U.S. to rise up like an uncoiled spring.

Investigating ground positioning data from GPS stations throughout the west, Scripps researchers Adrian Borsa, Duncan Agnew, and Dan Cayan found that the is causing an "uplift" effect up to 15 millimeters (more than half an inch) in California's mountains and on average four millimeters (0.15 of an inch) across the west. From the GPS data, they estimate the water deficit at nearly 240 gigatons (62 trillion gallons of water), equivalent to a six-inch layer of water spread out over the entire western U.S.

Results of the study, which was supported by the U.S. Geological Survey (USGS), appear in the August 21 online edition of the journal Science.

While poring through various sets of data of ground positions from highly precise GPS stations within the National Science Foundation's Plate Boundary Observatory and other networks, Borsa, a Scripps assistant research geophysicist, kept noticing the same pattern over the 2003-2014 period: All of the stations moved upwards in the most recent years, coinciding with the timing of the current drought.

Agnew, a Scripps Oceanography geophysics professor who specializes in studying earthquakes and their impact on shaping the earth's crust, says the GPS data can only be explained by rapid uplift of the tectonic plate upon which the western U.S. rests (Agnew cautions that the uplift has virtually no effect on the San Andreas fault and therefore does not increase the risk of earthquakes).

For Cayan, a research meteorologist with Scripps and USGS, the results paint a new picture of the dire hydrological state of the west.

"These results quantify the amount of water mass lost in the past few years," said Cayan. "It also represents a powerful new way to track water resources over a very large landscape. We can home in on the Sierra Nevada mountains and critical California snowpack. These results demonstrate that this technique can be used to study changes in fresh stocks in other regions around the world, if they have a network of GPS sensors."

Explore further: California Central Valley groundwater depletion slowly raises Sierra Nevada mountains

More information: "Ongoing drought-induced uplift in the western United States," by A.A. Borsa et al. Science, … 1126/science.1257750

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1 / 5 (5) Aug 21, 2014
Now if they had said "like a sponge cake in an oven", I would have bitten.
Now I'm just wondering if it's April 1st.
1 / 5 (2) Aug 21, 2014
"In hiking and climbing, it is not uncommon to find that the altitude measured by GPS is off by as much as 400 feet depending on satellite orientation." (http://en.wikiped...System).

"Knowing the current altitude of a satellite which can measure sea level to a precision of about 20 millimetres (e.g. the Topex/Poseidon system) is primarily complicated by orbital decay and the difference between the assumed orbit and the earth geoid. This problem is partially corrected by regular re-calibration of satellite altimeters from land stations whose height from MSL is known by surveying." (http://en.wikiped...suremen)

Seems there quite a bit of variation in opinions regarding the accuracy of satellite altimetry accuracy - yet we continually make projections far beyond those accuracy limits. It doesn't take much examination of studies like this to find them.
Bob Osaka
1 / 5 (2) Aug 22, 2014
Things expand when heated and contract when cooled. Ever seen a crack in a sidewalk caused by laying in the hot sun? It is always easier to explain what has happened than to predict what will. The Earth's crust is thin, paper thin some might say, some of the thinnest crust measured is in California's Death Valley.(some crust under the oceans may be thinner but as of yet not well defined by measurement) What will happen with the loss of the water table as a lubricant is anyone's guess.
The universe has an elegant balance of forces, the Earth also, when the balance is upset by anthropological activity things may go wildly wrong. Predicting the outcome is more than difficult, what is going on under our feet is not completely or even well understood. One day perhaps, someone will have to try to explain why California cracked like a hot sidewalk.

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