Drought-Induced Uplift in the Western United States as Observed by a GPS Network

Cayan, Daniel

Drought-Induced Uplift in the Western United States as Observed by a GPS Network

Presented on Wednesday, March 18, 2015

Adrian Borsa, Ph.D.¹, Daniel Cayan, Ph.D.¹ and Duncan Agnew², (1)Scripps Institution of Oceanography, La Jolla, CA, (2)University of California, La Jolla, CA

The western United States (WUS) 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 more than 700 continuously operating GPS stations in the EarthScope Plate Boundary Observatory and several smaller networks to measure this uplift, which reaches 15 mm in the California Coastal Ranges and Sierra Nevada and has a median value of 4 mm over the entire WUS. The pattern of mass loss due to the drought, which we recover from an inversion of uplift observations, ranges up to 50 cm of water equivalent and is consistent with observed decreases in precipitation and streamflow. We estimate the total deficit to be 240 Gt, equivalent to a uniform 10 cm layer of water over the entire region, or the magnitude of the current annual mass loss from the Greenland Ice Sheet. In the WUS, interannual changes in crustal loading are driven by changes in cool-season precipitation, which cause variations in surface water, snowpack, soil moisture, and groundwater. The results here demonstrate that the existing network of continuous GPS stations can be used to recover loading changes due to both wet and dry climate patterns. This suggests a new role for GPS networks such as that of the Plate Boundary Observatory. The exceptional stability of the GPS monumentation means that this network is also capable of monitoring the long-term effects of regional climate change. Surface displacement observations from GPS have the potential to expand the capabilities of the current hydrological observing network for monitoring current and future hydrological changes, with obvious social and economic benefits.

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Adrian Borsa, Ph.D.

Scripps Institution of Oceanography, La Jolla, CA

Adrian Borsa is a researcher at the Institute of Geophysics and Planetary Physics at the Scripps Institution of Oceanography. His work aims to describe how the shape of Earth's surface is changing at timescales of seconds to decades, and to link observed change to geophysical processes associated with phenomena ranging from earthquakes to climate change.

Daniel Cayan, Ph.D.

Scripps Institution of Oceanography, La Jolla, CA

Cayan’s work is aimed at understanding climate variability and changes over the Pacific Ocean and North America and how they affect the water cycle and related sectors over western North America. Cayan has specific interests in regional climate in California and has played a leading role in programs to deliver improved climate information to decision makers: the California Nevada Applications Program (CNAP), sponsored by the NOAA RISA Program and the Southwest Climate Science Center, sponsored by the US Geological Survey, Department of Interior, and the State of California in a series of climate vulnerability and adaptation assessments.

Duncan Agnew

University of California, La Jolla, CA

Duncan Agnew is Professor of Geophysics at the Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego. He studies long-term ground motions related to plate tectonics and earthquakes, and the effects of earth and ocean tides on these measurements.

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