Ongoing droughtinduced uplift in the western United States

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Ongoing drought-induced uplift in the western United States Adrian Antal Borsa, Duncan Carr Agnew,

Ongoing drought-induced uplift in the western United States Adrian Antal Borsa, Duncan Carr Agnew, Daniel R. Cayan Science, Volume 345, Issue 6204 26 September 2014

Justification for the Research • Severe drought in the western USA in 2013 -2014

Justification for the Research • Severe drought in the western USA in 2013 -2014 • Widespread availability of GPS data throughout the western USA • Abundant data available for stream discharge and precipitation, but very little data on Terrestrial Water Storage (vegetation and soil moisture, perennial snow and ice, groundwater, and surface water), and what data we have from GRACE is not very high resolution (several hundred kilometer spatial resolution) • Possibility of widespread uplift from reduction in mass loading by loss of water from a region

Research Premise • Daily positions from continuous GPS antennae from PBO and other smaller

Research Premise • Daily positions from continuous GPS antennae from PBO and other smaller networks • GPS detrended to remove secular velocity and seasonal water changes, excluded stations in active calderas and active groundwater pumping areas • Comparison of GPS vertical displacements to precipitation anomalies and stream discharge • Inverted for water mass loss associated with GPS-measured uplift

Results • Estimated an average of 5 mm of uplift, with certain areas up

Results • Estimated an average of 5 mm of uplift, with certain areas up to 15 mm of uplift (annual? ) during the period of study • Inverted to estimate 240 Gt of water mass loss in the Western USA • Calculated Coulomb stress change in southern California fault systems due to change in water mass (to test hypothesis that water mass changes influence fault activity)

Limitations • Assumes that this large-scale uplift is solely due to reduction in loading

Limitations • Assumes that this large-scale uplift is solely due to reduction in loading from water mass loss • Doesn’t have (or at least didn’t mention) independent data of groundwater, evapotranspiration, or other TWS changes in region