Saturday, November 01, 2014

Drought is causing regional uplift, provides estimates of water loss

Drought in the western U.S. has caused loss of water from the near-surface rocks that the crust is lighter and rising, according to a recent study published in the journal Science.  Based on the amount of uplift, they calculate the loss of 240 gigatons of water, equal to layer of water across the region 10-cm thick.   [Right, drought monitor, August, 2014. Courtesy of ADWR]

The abstract for the article is available online (
The western United States has been experiencing severe drought since 2013. The solid earth response to the accompanying loss of surface and near-surface water mass should be a broad region of uplift. We use seasonally adjusted time series from continuously operating global positioning system stations to measure this uplift, which we invert to estimate mass loss. The median uplift is 5 millimeters (mm), with values up to 15 mm in California’s mountains. The associated pattern of mass loss, ranging up to 50 centimeters (cm) of water equivalent, is consistent with observed decreases in precipitation and streamflow. We estimate the total deficit to be ~240 gigatons, equivalent to a 10-cm layer of water over the entire region, or the annual mass loss from the Greenland Ice Sheet.
But another study, by Don Argus at Jet Propulsion Lab and his colleagues, used the same algorithm as the Borsa et al team, found less uplift
and thus less water loss:
"California’s mountains subside up to 12 mm in the fall and winter due to the load of snow and rain and then rise an identical amount in the spring and summer when the snow melts, the rain runs off, and soil moisture evaporates."

"The seasonal surface water thickness change is 0.6 m in the Sierra Nevada, Klamath, and southern Cascade Mountains and decreases sharply to about 0.1 m east into the Great Basin and west toward the Pacific coast"

Adrian Antal Borsa, Duncan Carr Agnew, Daniel R. Cayan, 2014, "Ongoing drought-induced uplift in the western United States," Vol. 345 no. 6204 pp. 1587-1590
DOI: 10.1126/science.1260279

Argus, D. F., Y. Fu, and F. W. Landerer, (2014), Seasonal variation in total water storage in California inferred from GPS observations of vertical land motion, Geophys. Res. Lett., 41, 1971–1980, doi:10.1002/2014GL059570.

Thanks to Brian Conway at AZ Dept. of Water Resources for pointing me to the Argus et al, paper.

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