Detecting hydrologic deformation using GRACE and GPS

Hydrological processes cause variations in gravitational potential and surface deformations, both of which are de- tectable using space geodetic techniques. We computed elas- tic deformation using continental water load estimates de- rived from the Gravity Recovery and Climate Experiment and compared to 3D deformation estimated from GPS ob- servations. The agreement is very good in areas where large hydrologic signals occur over broad spatial scales, with cor- relation in horizontal components as high as 0.9. Agreement is also observed at smaller scales, including across Europe. This suggests that: a) both techniques are perhaps more accurate than previously thought and b) a large percent- age of the non-linear variations seen in our GPS time series are most likely related to geophysical processes rather than analysis error. Low correlation at some sites suggests that local processes or site specific analysis errors dominate the GPS deformation estimates rather than the broad-scale hy- drologic signals detected by GRACE.