Quantifying Changes in Water Loading in the U.S. Southwest via Comparison of GNSS, GRACE, and SWE Datasets

The synthesis of Gravity Recovery and Climate Experiment (GRACE) gravimetry data and Global Navigation Satellite System (GNSS) displacement data provides improved models of surface water hydrology. Much work remains to be done to understand the hydrological signal present in complementary geodetic data in much of the Western U.S., especially the Colorado River basin which comprises a diversity of climates due to its large expanse and highly variable topography. Here, we combine GNSS station vertical displacement data, GRACE surface mass change data, and snow water equivalent (SWE) data to quantify temporal changes in water distribution in the United States (U.S.) Southwest. We focus on a region composed of Arizona, New Mexico, Colorado, and Utah, allowing for the examination of variations in the Colorado River Basin, the primary source of water for the region's municipalities, agriculture, and ecosystems. We compare these three datasets using surface elastic deformation modeling, and use signal localization techniques to focus on the hydrological signal concentrated within the study region. We demonstrate that the accumulation and melt of snow have a first-order control on the timing of vertical displacement in the region. This is further demonstrated by phase delays between the signals of vertical surface displacement computed from each of the three datasets. These phase delays display a correlation between the distance to the nearest snowpack and the timing of vertical displacement measured at a given GNSS station.