Monitoring and comparison of terrestrial water storage changes in the northern high plains using GRACE and in-situ based integrated hydrologic model estimates

Enhanced measurement of the variation of the terrestrial water cycle are imperative to better understand the dynamics, water availability, and evaluate impacts of global changes on the water cycle. This study quantified storage in the various terrestrial water compartments using an integrated hydrologic model (IHM) - MIKE SHE that simulates the entire terrestrial water cycle and the Gravity Recovery and Climate Experiment (GRACE) satellite data in the intensively irrigated Northern High Plains (area ∼ 250,000 km2). The IHM, mainly constructed using in-situ data, was evaluated using field measured groundwater level, stream flow, and soil moisture data. The model was first used to calculate the incremental water storage for each water balance component (e.g. storage in the saturated zone) and then the GRACE equivalent terrestrial water storage anomaly. In the study area, storage in the saturated zone is the major component of the terrestrial water storage (TWS) anomaly. The GRACE-derived TWS anomaly and the anomaly simulated from the model are generally in agreement on a monthly scale with few discrepancies. Generally, both GRACE and the IHM results displayed a statistically significant increasing trend in the total TWS and groundwater storage anomalies from 2002-2013 over the Northern High Plains. This study demonstrates the applicability of an integrated hydrologic model to monitor TWS variations in a large area, and GRACE data and IHMs are capable of reproducing observed trends in TWS.