Relating Streamflow Discharge to Surface Elastic Response Under Hydrologic Loading Using Single GPS Vertical Displacement and the Storage-Discharge Relationship at Local Watershed Scales

Abstract

Uncertainties associated with climate change and increasing demands for water resources require better methods for estimating water availability at small to intermediate watershed scales (\u3c1500 km2). Temporal changes in watershed storage and transport across various watersheds in the western U.S. were investigated using the hydrologic loading signal from GPS vertical displacements as a proxy for changes in watershed total terrestrial storage. GPS vertical displacement and streamflow discharge relationships were analyzed at daily to monthly temporal resolution. Stream connected storage changes were inferred using discharge using a first-order dynamical system model. Storage inferred from discharge, GPS vertical displacement and storage inferred from a regional scale western U.S. GPS network array were compared. Analyzing the average behavior over the period of record (10+ years), we find that GPS vertical displacement is well correlated to discharge during periods of hydrograph recession resulting in R2 values ranging from (0.78 to 0.96) with 30-day smoothing. We show that local GPS measurements are in close agreement with regional GPS storage inferences. When GPS station array density is sparse, local GPS stations display better agreement with discharge inferred storage estimates and have the potential to provide higher spatial and temporal resolution relative to current published methods of inferring storage from regional GPS inversions. The GPS vertical displacement-discharge relationship provides an independent analysis of watershed function, insight into antecedent conditions, and strong correlations that may enhance predictive power when estimating water availability at local watershed scales most useful to hydrologist and water resources management