Abstract:
The Gravity Recovery and Climate Experiment (GRACE) twin satellites observe time variations in Earth's gravity field which yield crucial information about changes in terrestrial water storage (TWS). GRACE is characterized by low spatial (no better than ~500 km) and temporal (monthly) resolution but has the unique ability to sense water stored at all levels (including groundwater) systematically and continuously. The GRACE Data Assimilation System (GRACE-DAS) aims to tackle the challenges of assimilating coarse temporal and spatial resolution GRACE observations within the Catchment land surface model that runs at significantly finer resolutions. GRACE-DAS enhances the value of the GRACE water storage data by enabling spatial and temporal downscaling and vertical decomposition into moisture components (i.e. groundwater, soil moisture, snow), which individually are more useful for scientific applications. GRACE-DAS has been applied to North America in an effort to demonstrate that drought conditions can be identified more accurately and objectively by integrating spatially, temporally and vertically disaggregated GRACE data into the U.S. and North American Drought Monitors. Here we show the impact of the GRACE data assimilation on the simulation of hydrologic states across North America. An extensive dataset of groundwater storage from USGS monitoring wells are used to assess improvements in the hydrologic modeling skill resulting from the assimilation of GRACE TWS data. The potential value of GRACE assimilated moisture output for drought monitoring purposes across North America will also be discussed.