Based on satellite observations of Earth’s time variable gravity field from the Gravity Recovery and Climate Experiment (GRACE), it is possible to derive variations in terrestrial water storage, which includes groundwater, soil moisture, and snow. Given auxiliary information on the latter two, one can estimate groundwater storage variations. GRACE may be the only hope for groundwater depletion assessments in data-poor regions of the world. In this study, soil moisture and snow were simulated by the Global Land Data Assimilation System (GLDAS) and used to isolate groundwater storage anomalies from GRACE water storage data for the Mississippi River basin and its four major sub-basins. Results were evaluated using water level records from 58 wells set in the unconfined aquifers of the basin. Uncertainty in the technique was also assessed. The GRACE-GLDAS estimates compared favorably with the well based time series for the Mississippi River basin and the two sub-basins that are larger than 900,000 km². The technique performed poorly for the two sub-basins that have areas of approximately 500,000 km². Continuing enhancement of the GRACE processing methods is likely to improve the skill of the technique in the future, while also increasing the temporal resolution. A partir d’observations satellitaires du programme Gravity Recovery and Climate Experiment (GRACE), l’étude de la variation dans le temps du champ de gravité terrestre permet de déduire les variations du stock d’eau terrestre, ce qui comprend l’eau souterraine, l’humidité du sol et la neige. Les variations de stock d’eau souterraine peuvent être estimées à partir d’informations auxiliaires sur les deux autres composantes. GRACE pourrait être le seul espoir pour l’établissement des bilans d’eau souterraine dans les régions du monde où les données sont peu nombreuses. Dans cette étude concernant le bassin du fleuve Mississippi et ses quatre sous bassins principaux, l’humidité du sol et la neige ont été simulées par le modèle Global Land Data Assimilation System (GLDAS) et utilisées pour isoler les anomalies de stock d’eau souterraine à partir des données de stock d’eau du GRACE. Les résultats ont été évalués à partir d’enregistrements de niveaux piézomètriques réalisés dans 58 puits localisés dans les aquifères libres du bassin. L’incertitude liée à la technique a également été évaluée. Les estimations GRACE-GLDAS concordaient avec les chroniques de puits pour le bassin du Mississippi ainsi que pour les deux sous bassins présentant une superficie supérieure à 900,000 km². La technique s’est avérée peu performante pour les deux sous bassins d’environ 500,000 km². L’amélioration continue des méthodes de traitement des données du GRACE devrait à l’avenir augmenter la performance de la technique ainsi que la résolution temporelle. Es posible derivar variaciones en el almacenamiento de agua terrestre en base a observaciones de satélite del campo gravitacional temporal variable de la Tierra a partir del Experimento Clima y Recuperación de Gravedad (GRACE), el cual incluye agua subterránea, humedad del suelo, y nieve. Dada la información auxiliar de los dos últimos, uno puede estimar variaciones en almacenamiento de agua subterránea. GRACE puede ser la única esperanza para las evaluaciones de agotamiento de agua subterránea en regiones del mundo con datos pobres. En este estudio se simularon la nieve y humedad del suelo mediante el Sistema de Asimilación de Datos Globales del Terreno (GLDAS) y se usaron para aislar anomalías de almacenamiento de agua subterránea de los datos de almacenamiento de agua GRACE para la cuenca del Río Mississippi y sus cuatros sub-cuencas principales. Los resultados se evaluaron utilizando registros de niveles de agua para 58 pozos emplazados en acuíferos no confinados de la cuenca. También se evaluó la incertidumbre de la técnica. Los estimados provenientes de GLDAS-GRACE se comparan favorablemente con las series de tiempo de los pozos para la cuenca del Río Mississippi y las dos sub-cuencas cuyas áreas son mayores de 900,000 km². La técnica se desempeñó pobremente para las dos sub-cuencas que tienen áreas de aproximadamente 500,000 km². El mejoramiento continuo de los métodos de procesamiento GRACE es posible que mejore la habilidad de la técnica en el futuro mejorando al mismo tiempo la resolución temporal.

Recent developments in mascon (mass concentration) solutions for GRACE (Gravity Recovery and Climate Experiment) satellite data have significantly increased the spatial localization and amplitude of recovered terrestrial Total Water Storage anomalies (TWSA); however, land hydrology applications have been limited. Here we compare TWSA from April 2002 through March 2015 from (1) newly released GRACE mascons from the Center for Space Research (CSR‐M) with (2) NASA JPL mascons (JPL‐M), and with (3) CSR Tellus gridded spherical harmonics rescaled (sf) (CSRT‐GSH.sf) in 176 river basins, ∼60% of the global land area. Time series in TWSA mascons (CSR‐M and JPL‐M) and spherical harmonics are highly correlated (rank correlation coefficients mostly >0.9). The signal from long‐term trends (up to ±20 mm/yr) is much less than that from seasonal amplitudes (up to 250 mm). Net long‐term trends, summed over all 176 basins, are similar for CSR and JPL mascons (66–69 km³/yr) but are lower for spherical harmonics (∼14 km³/yr). Long‐term TWSA declines are found mostly in irrigated basins (−41 to −69 km³/yr). Seasonal amplitudes agree among GRACE solutions, increasing confidence in GRACE‐based seasonal fluctuations. Rescaling spherical harmonics significantly increases agreement with mascons for seasonal fluctuations, but less for long‐term trends. Mascons provide advantages relative to spherical harmonics, including (1) reduced leakage from land to ocean increasing signal amplitude, and (2) application of geophysical data constraints during processing with little empirical postprocessing requirements, making it easier for nongeodetic users. Results of this product intercomparison should allow hydrologists to better select suitable GRACE solutions for hydrologic applications.

Since March 2002, the Gravity Recovery and Climate Experiment (GRACE) has provided first estimates of land water storage variations by monitoring the time‐variable component of Earth's gravity field. Here we characterize spatial‐temporal variations in terrestrial water storage changes (TWSC) from GRACE and compare them to those simulated with the Global Land Data Assimilation System (GLDAS). Additionally, we use GLDAS simulations to infer how TWSC is partitioned into snow, canopy water and soil water components, and to understand how variations in the hydrologic fluxes act to enhance or dissipate the stores. Results quantify the range of GRACE‐derived storage changes during the studied period and place them in the context of seasonal variations in global climate and hydrologic extremes including drought and flood, by impacting land memory processes. The role of the largest continental river basins as major locations for freshwater redistribution is highlighted. GRACE‐based storage changes are in good agreement with those obtained from GLDAS simulations. Analysis of GLDAS‐simulated TWSC illustrates several key characteristics of spatial and temporal land water storage variations. Global averages of TWSC were partitioned nearly equally between soil moisture and snow water equivalent, while zonal averages of TWSC revealed the importance of soil moisture storage at low latitudes and snow storage at high latitudes. Evapotranspiration plays a key role in dissipating globally averaged terrestrial water storage. Latitudinal averages showed how precipitation dominates TWSC variations in the tropics, evapotranspiration is most effective in the midlatitudes, and snowmelt runoff is a key dissipating flux at high latitudes. Results have implications for monitoring water storage response to climate variability and change, and for constraining land model hydrology simulations.

Using time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission, we estimate ice mass changes over Greenland during the period April 2002 to November 2005. After correcting for the effects of spatial filtering and limited resolution of GRACE data, the estimated total ice melting rate over Greenland is –239 ± 23 cubic kilometers per year, mostly from East Greenland. This estimate agrees remarkably well with a recent assessment of –224 ± 41 cubic kilometers per year, based on satellite radar interferometry data. GRACE estimates in southeast Greenland suggest accelerated melting since the summer of 2004, consistent with the latest remote sensing measurements.

Time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions have opened up a new avenue of opportunities for studying large-scale mass redistribution and transport in the Earth system. Over the past 19 years, GRACE/GRACE-FO time-variable gravity measurements have been widely used to study mass variations in different components of the Earth system, including the hydrosphere, ocean, cryosphere, and solid Earth, and significantly improved our understanding of long-term variability of the climate system. We carry out a comprehensive review of GRACE/GRACE-FO satellite gravimetry, time-variable gravity fields, data processing methods, and major applications in several different fields, including terrestrial water storage change, global ocean mass variation, ice sheets and glaciers mass balance, and deformation of the solid Earth. We discuss in detail several major challenges we need to face when using GRACE/GRACE-FO time-variable gravity measurements to study mass changes, and how we should address them. We also discuss the potential of satellite gravimetry in detecting gravitational changes that are believed to originate from the deep Earth. The extended record of GRACE/GRACE-FO gravity series, with expected continuous improvements in the coming years, will lead to a broader range of applications and improve our understanding of both climate change and the Earth system.

The Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission provides a new capability for measuring extreme climate events, such as floods and droughts associated with large‐scale terrestrial water storage (TWS) change. GRACE gravity measurements show significant TWS increases in the lower Amazon basin in the first half of 2009, clearly associated with the exceptional flood season in that region. The extended record of GRACE monthly gravity solutions reveals the temporal and spatial evolution of both nonseasonal and interannual TWS change in the Amazon basin over the 7 year mission period from April 2002 to August 2009. GRACE observes a very dry season in 2002–2003 and an extremely wet season in 2009. In March 2009 (approximately the peak of the recent Amazon flood), total TWS surplus in the entire Amazon basin is ∼624 ± 32 Gt, roughly equal to U.S. water consumption for a year. GRACE measurements are consistent with precipitation data. Interannual TWS changes in the Amazon basin are closely connected to ENSO events in the tropical Pacific. The 2002–2003 dry season is clearly tied to the 2002–2003 El Niño and the 2009 flood to the recent La Niña event. The most significant contribution of this study in the area of water resources is to confront the hydrological community with the latest results of the GRACE satellite mission and further demonstrates the unique strength of GRACE and follow‐up satellite gravity observations for measuring large‐scale extreme climate events.