Mapping the onset and severity of drought is of critical national importance. The Western Governor's Association, in proposing a National Integrated Drought Information System (NIDIS), has recognized the U.S. and North American Drought Monitors (USDM; NADM) as important tools for minimizing drought impacts, yet both are limited by the inadequacy of current soil moisture and groundwater observation networks. NASA's Gravity Recovery and Climate Experiment (GRACE) satellites are unique in their ability to measure variations in water stored at all levels above and within the land surface. However, GRACE is currently underutilized for hydrological applications due to the coarseness of the products: monthly, >150,000 km2, and unstratified. The Catchment Land Surface Model (CLSM) simulates groundwater, soil moisture, and snow water storage, using physical parameterizations of hydrological processes. While its resolution is high, accuracy is limited by input data quality and simplifications required for computational efficiency. Recently, three of the investigators developed a data assimilation scheme (DAS) to disaggregate GRACE observations spatially and temporally within CLSM, with remarkable results. We propose to integrate GRACE-DAS products into the USDM and NADM. Assimilated groundwater and soil moisture fields will be systematically incorporated into the objective blends which constitute DM baselines. The original objective blends, serving as benchmarks, will be compared with GRACE-integrating versions. We will refine the GRACE-DAS configuration and optimize the objective blend weighting using several a posteriori measures of drought severity. These metrics and stakeholder feedback will be used to quantify improvement in the USDM and NADM due to inclusion of GRACE-DAS fields. The proposed project will benefit the Water Resources, Agricultural Efficiency, and Disaster Management national application areas. In particular, it will reduce uncertainty in the management of surface and aquifer water resources through its novel use of GRACE data for mapping drought severity.