The influence of uncertainty: assessing anthropogenic drivers in GRACE observations

Abstract:

Global groundwater depletion has largely been attributed to human use, whereby extractions exceed natural recharge rates resulting in a loss of groundwater storage over time. Exploration of relations between natural and human drivers and observations of groundwater storage change derived from the Gravity Recovery and Climate Experiment (GRACE) are critical to differentiate factors that produce observable changes in groundwater storage. A key variable expected to induce change in storage is groundwater pumping rates, available for the contiguous U.S. in 5-year intervals from the U.S. Geological Survey. Previous studies quantified weak influence of groundwater pumping to GRACE-derived groundwater storage change, a result attributed to equilibrium conditions in groundwater storage after long-term pumping. These results, however, beg the question: how does uncertainty in groundwater pumping data influence our interpretation of anthropogenic drivers recorded in GRACE observations? In this study, a range of interpolated groundwater pumping time series are evaluated to understand the influence of uncertainty in monthly groundwater responses observed by GRACE. Results of the study highlight the importance of uncertainty in auxiliary variables to interpret the role of anthropogenic influences to observed groundwater storage change.