Severe Drought is Causing the Western U.S. to Rise


The following UC San Diego News Center press release is by Mario Aguilera, dated August 21, 2014, and titled “Severe drought is causing the western U.S. to rise: Scientists use GPS technology to track uplift from recent massive loss of water, estimated at 63 trillion gallons”:

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 water shortage 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 (63 trillion gallons of water), equivalent to a four-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 water stocks in other regions around the world, if they have a network of GPS sensors.”

Image 1 for article titled "Severe Drought is Causing the Western U.S. to Rise"
Detrended daily vertical displacements from 771 continuous GPS stations in the western USA, decimated to weekly intervals for plotting (gray lines). The thick red line is the median value of all data for each day and the light red lines indicate the standard deviation computed from the interquartile range. The uplift that began in 2013 is remarkable for the period after 2006, when the number and distribution of GPS stations greatly expanded across the region with the building of the Plate Boundary Observatory (blue line shows the number of stations used in the analysis) (from the Science article)

Image 2 for article titled "Severe Drought is Causing the Western U.S. to Rise"
Spatial distribution of displacements from the timeseries on March 1 of 2011 through 2014. Uplift is indicated by yellow-red colors and subsidence by shades of blue. Gray region is where stations were excluded in the Central Valley of California. Adrian Borsa, an assistant research geophysicist at Scripps Institution of Oceanography, UC San Diego (Ibid.)

Image 3 for article titled "Severe Drought is Causing the Western U.S. to Rise"
Maps of estimated loads and predicted and residual displacements: (A) Loading estimate for the western USA in March 2014. Redder areas indicate negative loading (mass deficit relative to the 2003-2012 mean), bluer areas indicate positive loading (mass surplus), and white areas are unchanged. (B) Vertical displacements corresponding to loading model in left panel, at the locations of the GPS stations used in this analysis (compare to actual displacements in rightmost panel of Fig. 2) (Ibid.)