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Information on water storage changes in the soil can globally be obtained from different types of satellite observations. While microwave remote sensing is limited to the upper few centimeters of the soil, satellite gravimetry can detect changes in the full column of terrestrial water storage (TWS), but cannot distinguish between storage variations in different soil depths. Jointly analyzing both data types promises insights into the underlying hydrological dynamics and may enable a better process understanding of water storage change in the subsurface. In this study, we investigate the global relationship of (1) several satellite soil moisture (SM) products and (2) non-standard daily TWS data from the GRACE/-FO satellite gravimetry missions. The analysis of these data on a daily basis could be beneficial for identifying hydro-climatic extreme events such as heavy precipitation or flood events. Therefore, we evaluate the correspondence of particularly high and low percentiles in both TWS and SM time series to identify extreme events. We discuss the different temporal dynamics in near-surface SM vs. TWS before and after flood and drought events to identify antecedent conditions leading to floods and recovery times after droughts in different storage compartments. Furthermore, temporally high-frequency variations are discussed using sub-monthly SM and TWS variations derived by high-pass filtering. We find increasingly large correlations between the TWS and SM for deeper SM integration depths (root zone vs. surface layer). Even for high-pass-filtered (sub-monthly) variations, significant correlations of up to 0.6 can be found in regions with large high-frequency variability., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

In 2019 the Combination Service for Time-variable Gravity fields (COST-G) started operation with the release of the complete time-series of combined GRACE monthly gravity fields COST-G GRACE RL01. Meanwhile additional time-series of monthly GRACE gravity fields have become available, mainly from Chinese analysis centers. The COST-G quality control confirms the high quality of these solutions that are derived with independent analysis tools.In the frame of the Horizon 2020 project Global Gravity-based Groundwater Product (G3P) the weighting scheme of the monthly GRACE-FO gravity fields was adapted to take into account the limitations on the solution space imposed by the specific observation geometry of the GRACE/GRACE-FO missions.We present the new COST-G GRACE RL02 combination, based on an extended set of time-series including COST-G's new Chinese partners, and combined applying the G3P weighting scheme., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

International audience; The German Research Unit GlobalCDA has the goal to improve the predictive skills of hydrological models by combining remote sensing information using a calibration/data assimilation (C/DA) approach. In order to validate model results and to assess the success of the C/DA efforts, independent data sets are crucially needed, such as in-situ groundwater observations to assess the ability of the model to describe groundwater storage changes. The main challenge arising from such comparisons is to capture basin-scale groundwater storage from a set of in-situ GW observations settled in highly heterogeneous lithologies with irregular & non-homogeneous sampling. Furthermore, the conversion from groundwater (GW) level measurements to storage variations requires information on specific yield, ideally given site-specific for each monitoring well. However, this information is largely not available and difficult to estimate in areas with highly heterogeneous geology.In our study we use a data set of groundwater level observations at about 3000 groundwater monitoring wells in France. Based on a high-resolution hydro-geological information system provided by the French geological survey (BRGM) and water authorities (BDLISA), we assign the borehole data to individual hydro-geological units. For the upscaling to river basin averages, we (i) aggregate the measurements that originate from the same unit and (ii) account for the areal fractions of the hydro-geological units within the river basin. For the interpretation of GW level variations to GW storage changes, we tested several approaches to estimate specific yield values for the individual hydro-geological units. Wherever possible, we use the specific yield values explicitly provided in the BDLISA data base, mostly estimated from pumping test analysis. When not available, we assign literature-based specific yield values based on the detailed lithological information provided for each unit. This method is compared to global porosity information provided by low resolution geological data from GHYLMPS (Gleeson et al., 2014)Besides presenting the methodological approach, this presentation shows the resulting groundwater storage time series, averaged for individual river basins in France and for individual 0.5° grid cells. Additionally, comparisons to simulated groundwater storage variations of the WaterGAP Global Hydrology Model (WGHM) will be presented. We discuss the sensitivity of basin averaged GW storage time series to different choices of specific yield for individual boreholes.How to cite: Hsu, K.-H., Eicker, A., Hasan, M., Güntner, A., and Longuevergne, L.: Estimating groundwater storage changes for major river basins in France using a regional groundwater data set , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7127, https://doi.org/10.5194/egusphere-egu22-7127, 2022.

The application of terrestrial water storage (TWS) data observed with GRACE and GRACE-FO often requires realistic uncertainties. For gridded TWS data, this requires the knowledge of the covariances, which can be derived from the formal, i. e. formally estimated in the parameter estimation, variance-covariance matrix provided together with the Stokes coefficients. However, the propagation of monthly variance-covariance matrices to TWS data is computationally expensive, so we apply a spatial covariance model for TWS data. The covariance model provides non-homogeneous (location depending), non-stationary (time depending), and anisotropic (orientation depending) covariances between any two given points. Further, the model accommodates wave-like behaviour of East-West-directed covariances, which residuals of GRACE striping errors can cause. The main application of such spatial covariances is the estimation of uncertainties for mean TWS time series for arbitrary regions such as river basins. Alternatively, regional uncertainties can be derived from the above mentioned formal variance-covariance matrices of the Stokes coefficients. This study compares modelled basin uncertainties for GFZ RL06 and ITSG-Grace2018 TWS data with the formal basin uncertainties from the ITSG-Grace2018 solution. The modelled and formal uncertainties fit both in the spatial and temporal domain. We further evaluate the modelled uncertainties by comparison to empirical uncertainties over arid regions. Here, again the appropriateness of the modelled uncertainties is shown. The results, namely the TWS uncertainties for global river basins, are available via the GravIS portal. Further, we provide a Python toolbox, which allows computing uncertainties and covariance matrices.

The International Combination Service for Time-variable Gravity Fields (COST-G) is a Product Center of IAG’s International Gravity Field Service (IGFS). COST-G provides consolidated monthly global gravity fields in terms of spherical harmonic coefficients and thereof derived grids of surface mass changes by combining existing solutions or normal equations from COST-G analysis centers (ACs) and partner analysis centers (PCs). The COST-G ACs adopt different analysis methods but apply agreed-upon consistent processing standards to deliver time-variable gravity field models from GRACE/GRACE-FO low-low satellite-to-satellite tracking (ll-SST) and from Swarm GPS high-low satellite-to-satellite tracking (hl-SST). The poster presents the organizational structure of COST-G and results from the first releases of combined monthly GRACE and GRACE-FO solutions. In addition, the perspectives from the provision of deterministic signal models (DSM), allowing for a few months prediction and therefore application in operational precise orbit determination activities of low Earth satellites, are discussed.

The satellite missions GRACE and GRACE-FO, dedicated to the observation of the time-variable Earth gravity field, provide invaluable insight into continental total water storage, continental ice mass change and ocean mass change at spatial scales of 200-400 km and monthly time-resolution, covering the time-period 2002 to present. The Combination Service for Time-Variable Gravity Fields (COST-G) of the International Association of Geodesy (IAG) collects the monthly gravity fields of its associated or partner Analysis Centers (ACs) and performs a weighted combination to provide a consolidated time-series of monthly gravity fields at Level-2 (spherical harmonic coefficients) and user-friendly Level-3 (post-processed global grids) products. Gaps in the GRACE or GRACE-FO time-series may be bridged by monthly gravity fields derived from orbits of the Swarm satellites, dedicated to the observation of the Earth magnetic field, at the cost of significantly reduced spatial resolution. COST-G performs quality control and harmonization of the contributing GRACE, GRACE-FO or Swarm time-series. The combined gravity fields undergo consistency checks and internal validation by the COST-G validation centers at GFZ and GRGS. An independent board of experts in hydrological, oceanic and cryosphere applications irregularly performs external validations. A combined re-processed GRACE time-series COST-G GRACE RL01 is available at the International Center for Global Earth Models ICGEM (L2-products) or the Gravity Information Service GRAVIS (L3-products), both operated by GFZ. The operational GRACE-FO time-series is updated regularly with a latency of less than 3 months, Swarm gravity fields are operationally combined in a quarterly processing scheme.

We present the operational GRACE-FO combined time-series of monthly gravity fields of the Combination Service for Time-variable Gravity fields (COST-G) of the International Association of Geodesy (IAG). COST-GGRACE-FORL01operational is combined at AIUB and relies on operational monthly solutions of the COST-G Analysis Centers GFZ, GRGS, IfG, LUH and AIUB and the associated Analysis Centers CSR and JPL. All COST-G Analysis Centers have passed a benchmark test to ensure consistency between the different processing approaches and all of the contributing time-series undergo a strict quality control focusing on the signal content in river basins and polar regions with pronounced changes in ice mass to uncover any regularization that may bias the combination. The combination is performed by variance component estimation on the solution level, the relative monthly weights thus providing valuable and independent insight into the consistency and noise levels of the individual monthly contributions. The combined products then are validated internally in terms of noise, approximated by the non-secular, non-seasonal variability over the oceans. Once they have passed this quality control the combined gravity fields are assessed by an external board of experts who evaluate them in terms of orbit predictions, lake altimetry, river hydrology or oceanography.

With the release of the combined GRACE monthly gravity field time-series COST-G RL01 the Combination Service for Time-variable Gravity fields (COST-G) of the International Association of Geodesy (IAG) became operational in July 2019. We present the COST-G RL01 time-series and provide validation in terms of orbit fit, ice mass trends, lake altimetry and sea level budget. We identify weak points in the combined monthly gravity fields and discuss possible improvements of the combination strategy for future combinations. While COST-G RL01 is based on sets of re-processed GRACE monthly gravity fields, COST-G also provides combinations of monthly Swarm high-low satellite-to-satellite tracking (hl-SST) gravity fields on an operational basis with a latency of 3 months. Combinations of GRACE-FO monthly gravity fields are in the process of operationalization. We provide a status report and first results of GRACE-FO combinations. Combined GRACE, Swarm and GRACE-FO gravity fields complement each other to provide a long-term time-series of mass variation in the system Earth.

Příručka geodetů je vydávána Mezinárodní asociací geodézie (IAG) pravidelně po každém Valném shromáždění IUGG / IAG. Cílem je představit současnou strukturu IAG a její specifikace a seznámit širokou geodetickou komunitu s působností a pracovníky složek asociace pro nadcházející legislativní období. Vědecký program a plánované činnosti jsou podrobně popsány. První část příručky 2020 představuje historický vývoj a současné předpisy IAG (stanovy, stanovy a pravidla revidované během Valného shromáždění IUGG / IAG 2019). Druhá část shrnuje výsledky Valného shromáždění IAG konaného ve spojení s 27. Valným shromážděním IUGG v kanadském Montrealu v červenci 2019. Přehled nejdůležitějších výsledků IAG od roku 2015 do roku 2019 je uveden v projevu prezidenta. Publikovány jsou citace vědců vyznamenaných v Montrealu nejvyššími oceněními IAG (Levalloisova medaile, Cena Guy Bomforda a Cena mladých autorů). Tento oddíl uzavírají zprávy generálního tajemníka, zasedání Rady a výkonného výboru IAG a rezoluce IUGG a IAG. Třetí část příručky obsahuje podrobné struktury a programy na období 2019--2023. Všechny komponenty IAG (komise, mezikomisní výbor, komunikační a terénní pobočka, služby a globální geodetický pozorovací systém) jsou prezentovány spolu s jejich dílčími složkami (subkomise, projekty, studijní skupiny a pracovní skupiny). Tato část popisuje plánovanou vědeckou práci IAG v následujících letech. Čtvrtá část doplňuje příručku o některé obecné informace užitečné pro geodetickou komunitu. Zvýrazněno je internetové zastoupení IAG a publikační řada a jsou zde uvedeny národní delegáti a zástupci IAG pro služby a mezinárodní vědecké orgány. The Geodesist’s Handbook is published by the International Association of Geodesy (IAG) periodically after each IUGG/IAG General Assembly. The objective is to present the current IAG structure and its specifications, and to introduce the terms of reference and the officers of the Association’s components for the upcoming legislative period to the broad geodetic community. The scientific program and planned activities are described in detail. The first part of the Handbook 2020 presents the historical developments and current regulations of the IAG (Statutes, Bylaws and Rules as reviewed during the IUGG/IAG General Assembly 2019). The second part summarises the outcome of the IAG General Assembly held in conjunction with the 27th IUGG General Assembly in Montreal, Canada, in July 2019. An overview of the most important IAG results from 2015 to 2019 is given in the presidential address. The citations of thescientists decorated in Montreal with the highest IAG awards (Levallois Medal, Guy Bomford Prize, and Young Authors Award) are published. Reports of the Secretary General, the IAG Council and Executive Committee meetings, and the IUGG and IAG resolutions conclude this section. The third part of the Handbook contains the detailed structures and programs for the period 2019-2023. All IAG components (Commissions, Inter-commission Committee, Communication and Outreach Branch, Services, and the Global Geodetic Observing System) are presented along with their sub-components (Sub-commissions, Projects, Study Groups and Working Groups). This part describes the planed scientific work of IAG during the coming years. The fourth part completes the Handbook with some general information useful for the geodetic community. The IAG Internet representation and the publication series are highlighted, and the IAG national delegates and representatives to services and international scientific bodies are listed.

The hydrological budget of a region is determined based on the horizontal and vertical water fluxes acting in both inward and outward directions. These integrated water fluxes vary, altering the total water storage and consequently the gravitational force of the region. The time-dependent gravitational field can be observed through the Gravity Recovery and Climate Experiment (GRACE) gravimetric satellite mission, provided that the mass variation is above the sensitivity of GRACE. This study evaluates mass changes in prominent reservoir regions through three independent approaches viz. fluxes, storages, and gravity, by combining remote sensing products, in-situ data and hydrological model outputs using WaterGAP Global Hydrological Model (WGHM) and Global Land Data Assimilation System (GLDAS). The results show that the dynamics revealed by the GRACE signal can be better explored by a hybrid method, which combines remote sensing-based reservoir volume estimates with hydrological model outputs, than by exclusive model-based storage estimates. For the given arid/ semi-arid regions, GLDAS based storage estimations perform better than WGHM.

International audience; Using data from the Gravity Recovery And Climate Experiment (GRACE) mission, we derive statistically robust " hot spot " regions of high probability of peak anomalous—i.e., with respect to the seasonal cycle—water storage (of up to 0.7 m one-in-five-year return level) and flux (up to 0.14 m/month). Analysis of, and comparison with, up to 32 years of ERA-Interim reanalysis fields reveals generally good agreement of these hot spot regions to GRACE results and that most exceptions are located in the tropics. However, a simulation experiment reveals that differences observed by GRACE are statistically significant, and further error analysis suggests that by around the year 2020, it will be possible to detect temporal changes in the frequency of extreme total fluxes (i.e., combined effects of mainly precipitation and floods) for at least 10–20% of the continental area, assuming that we have a continuation of GRACE by its follow-up GRACE Follow-On (GRACE-FO) mission.

International audience; Atmospheric and terrestrial water budgets, which represent important boundary conditions for both climate modelingand hydrological studies, are linked by evapotranspiration (E) and precipitation (P). These fields are providedby numerical weather prediction models and atmospheric reanalyses such as ERA-Interim and MERRA-Land;yet, in particular the quality of E is still not well evaluated. Via the terrestrial water budget equation, water storagechanges derived from products of the Gravity Recovery and Climate Experiment (GRACE) mission, combinedwith runoff (R) data can be used to assess the realism of atmospheric models.While on short temporal scales (inter-annual down to sub-seasonal) the modeled fluxes agree remarkablywell with GRACE water storage changes, the models exhibit large biases and fail to capture the long-term fluxtrends in P-E-R corresponding to GRACE accelerations (Eicker et al. 2016). This leads to the assumption thatdespite the short time span of available gravity field observations, GRACE is able to provide new information forconstraining the long-term evolution of water fluxes in future atmospheric reanalyses.In this contribution we will investigate the agreement of GRACE water storage changes with P-E-R fluxtime series from different (global and regional) atmospheric reanalyses, land surface models, as well asobservation-based data sets. We will perform a global analyses and we will additionally focus on selected riverbasins. The investigations will be carried out for various temporal scales, focussing on the short-term fluxes(month-to-month variations), for which models and GRACE agree well with correlations of the de-trended andde-seasoned fluxes time series reaching up to 0.8 and more. We will furthermore extent the study towards evenhigher temporal frequencies, investigating whether the modeled and observed fluxes show sub-monthly variabilitythat can be detected in daily GRACE time series.Eicker, A., E. Forootan, A. Springer, L. Longuevergne, J. Kusche (2016) Does GRACE see the terrestrialwater cycle ’intensifying’? Journal of Geophysical Research - Atmosphere, in press

International audience; Several researchers have postulated that, under a changing climate due to anthropogenic forcing, an intensification of the water cycle is already under way. This is usually related to increases in hydrological fluxes as precipitation (P), evapotranspiration (E), and river discharge (R). It is under debate, however, whether such observed or reconstructed flux changes are real and on what scales. Large-scale increase or decrease of the flux deficit (P-E-R), i.e. flux changes that do not compensate, would lead to acceleration or deceleration of water storage anomalies potentially visible in GRACE data. In agreement with earlier studies, we do find such accelerations in global maps of gridded GRACE water storage anomalies over 2003-2012. However, these have been generally associated with interannual and decadal climate variability. Yet, we show that even after carefully isolating and removing the contribution of El Nino that partially masks long-term changes, using a new method, accelerations of up to 12mm/yr2 remain in regions such as Australia, Turkey, and Northern India. We repeat our analysis with flux fields from two global atmospheric reanalyses that include land surface models (ERA-Interim, MERRA-Land). While agreeing well with GRACE on shorter time scales, they fall short in displaying long-term trends corresponding to GRACE accelerations. We hypothesize that this may be due to time-varying biases in the reanalysis fluxes as noticed in other studies. We conclude that even though its data record is short, GRACE provides new information that should be used to constrain future reanalyses towards a better representation of long-term water cycle evolution.

International audience; In an internationally coordinated initiative among the main user communities of gravity field products thescience and user requirements for a future gravity field mission constellation (beyond GRACE-FO) have beenreviewed and defined. This activity was realized as a joint initiative of the IAG (International Association ofGeodesy) Sub-Commissions 2.3 and 2.6, the GGOS (Global Geodetic Observing System) Working Group onSatellite Missions, and the IUGG (International Union of Geodesy and Geophysics). After about one year ofpreparation, in a user workshop that was held in September 2014 consensus among the user communities ofhydrology, ocean, cryosphere, solid Earth and atmosphere on consolidated science requirements could be achieved.The consolidation of the user requirements became necessary, because several future gravity field studieshave resulted in quite different performance numbers as a target for a future gravity mission (2025+). Based onlimited number of mission scenarios which took also technical feasibility into account, a consolidated view onthe science requirements among the international user communities was derived, research fields that could not betackled by current gravity missions have been identified, and the added value (qualitatively and quantitatively) ofthese scenarios with respect to science return has been evaluated. The resulting document shall form the basis forfurther programmatic and technological developments.In this contribution, the main results of this initiative will be presented. An overview of the specific requirementsof the individual user groups, the consensus on consolidated requirements as well as the new researchfields that have been identified during this process will be discussed.

International audience

International audience; Global hydrological models contribute to the understanding and quantification of the global water cycle. However, large uncertainties persist on the one hand due to the simplified representation of hydrological processes for a global scale analysis and, on the other hand due to input data uncertainties, e.g. climate forcing and data to the anthropogenic alteration of the water cycle. The time-variable solutions of the Gravity Recovery And Climate Experiment (GRACE) mission provide an independent observation of water storage change with global coverage, which can be used to improve global hydrological models. For this purpose, an ensemble Kalman filter approach is applied to assimilate GRACE total water storage (TWS) change grids into the WaterGAP Global Hydrology Model (WGHM). In contrast to existing studies, our approach involves the full error information of the GRACE solutions, i.e. spatial correlations, as well as the full spatial resolution of the data. To guarantee a realistic estimation of the uncertainties introduced by the climate forcing data, their covariance matrices are determined from an ensemble of forcing fields from different state-of-the-art climate inputs. Finally, the errors are propagated to the assimilated water storage outputs. Here, the results are presented with respect to the precipitation input.

GRACE gravity field reprocessing at IGG Bonn

The Earth's gravity field is determined within the BMBF project REeal data AnaLysis GOCE (REALGOCE).

This dissertation focuses on the development of regional gravity field refinement methods and their realization based on the combination of data from different observation techniques using series expansions in terms of spherical radial basis functions. Terrestrial, airborne, and shipborne measurements are combined with satellite altimetry and satellite gravimetry data to derive high-resolution and high-precision (quasi-) geoid models, which are the key for the realization of the International Height Reference System. Diese Dissertation befasst sich mit der Entwicklung von Methoden zur Verfeinerung regionaler Schwerefelder sowie deren Umsetzung durch Kombination von Daten verschiedener Beobachtungstechniken unter Verwendung sphärischer radialer Basisfunktionen. Terrestrische Messungen werden dabei mit denen der Flug-, Schiffs- und Satellitengravimetrie sowie der Satellitenaltimetrie kombiniert, um hochaufgelöste und hochpräzise (Quasi-) Geoidmodelle für die Realisierung des Internationalen Höhenreferenzsystems zu erhalten.

Dedicated satellite gravity missions observe the mass transportation and redistribution of Earth’s mass. This study focuses on possible future sallite gravity constellations based on the GRACE concept. Their potential performance is evaluated via closed-loop simulations assessing the key performance parameters. The possibilities with multi-pair constellations are evaluated using a near-real time processing scheme and a flood detection processing algorithm. Schwerefeld-Satellitenmission beobachten die Massernveränderung der Erde. Der Fokus dieser Arbeit liegt auf möglichen zukünftigen Konstellationen basierend auf dem GRACE-Konzept. Die Performance unter Berücksichtigung der wichtigsten Parameter wurde mittels “closed-loop” Simulation getestet. Die Möglichkeiten mit mehreren Satellitenpaaren sind mittels Near-Real Time Schemas und eines Algorithmus für die Überflutungsdetektion evaluiert worden.