Improvement of Global Hydrological Models Using GRACE Data

Abstract

After about six years of GRACE (Gravity Recovery and Climate Experiment) satellite mission operation, an unprecedented global data set on the spatio-temporal variations of the Earth's water storage is available. The data allow for a better understanding of the water cycle at the global scale and for large river basins. This review summarizes the experiences that have been made when comparing GRACE data with simulation results of global hydrological models and it points out the prerequisites and perspectives for model improvements by combination with GRACE data. When evaluated qualitatively at the global scale, water storage variations on the continents from GRACE agreed reasonably well with model predictions in terms of their general seasonal dynamics and continental-scale spatial patterns.Differences in amplitudes and phases of water storage dynamics revealed in more detailed analyses were mainly attributed to deficiencies in the meteorological model forcing data, to missing water storage compartments in the model, but also to limitations and errors of the GRACE data. Studies that transformed previously identified model deficiencies into adequate modifications of the model structure or parameters are still rare. Prerequisites for a comprehensive improvement of large-scale hydrological models are in particular the consistency of GRACE observation and model variables in terms of filtering, reliable error estimates, and a full assessment of the water balance. Using improvements in GRACE processing techniques, complementary observation data, multi-model evaluations and advanced methods of multi-objective calibration and data assimilation, considerable progress in large-scale hydrological modelling by integration of GRACE data can be expected.

Understanding terrestrial water storage variations in northern latitudes across scales

“…Due to their global coverage and independence from surface conditions, the data represent a unique opportunity to quantify spatio-temporal variations of the Earth's water resources (Alkama et al, 2010;Werth et al, 2009). Therefore, GRACE data have been widely used to diagnose patterns of hydrological variability (Seo et al, 2010;Rodell et al, 2009;Ramillien et al, 2006;Feng et al, 2013), to validate and improve model simulations Güntner, 2008;Werth and Güntner, 2010;Chen et al, 2017;Eicker et al, 2014;Girotto et al, 2016;Schellekens et al, 2017), and to enhance our understanding of the water cycle on regional to global scales (Syed et al, 2009;Felfelani et al, 2017).…”

“…To facilitate insight into the underlying processes, hydrological models are frequently used to separate the measured TWS into its different components such as groundwater, soil moisture, and snowpacks (Felfelani et al, 2017). However, as a consequence of uncertain model structure, forcing, and parametrization, model-based partitioning is ambiguous (Güntner, 2008) and may lead to diverging conclusions, especially on regional scale (Long et al, 2015;Schellekens et al, 2017).…”

“…Recently, several studies showed the benefits of additionally including GRACE TWS data in model calibration (Werth and Güntner, 2010;Xie et al, 2012;Chen et al, 2017) or by means of data assimilation Forman et al, 2012;Kumar et al, 2016). However, although these approaches improve model simulations, they do not reduce the uncertainty in the partitioning of TWS due to the parameter equifinality problem (Güntner, 2008). Therefore, it is desirable to include multiple observations, ideally of several hydrological storages and fluxes, to constrain model results (Syed et al, 2009).…”

Combination of GRACE monthly gravity field solutions from different processing strategies

“…Using the K -band and GPS measurements from the GRACE twin satellites (Dunn et al 2003), gravity fields at various spatial scales and temporal resolutions have been derived. They have been used for a wide range of geoscience research such as geodesy, hydrology, oceanography, atmo-B Ulrich Meyer ulrich.meyer@aiub.unibe.ch 1 Astronomical Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland spheric science, and glaciology (e.g., Güntner 2008;Johnson and Chambers 2013;Steffen et al 2009; and an overview in Wouters et al 2014).…”

Modelling Freshwater Resources at the Global Scale: Challenges and Prospects

“…Nevertheless, the particular nature of GRACE TWS data based on the Earth's time-variable gravity field requires specific consideration of the storage compartments considered, data filtering and error terms to make the calibration scheme consistent between model and observations (Güntner 2008). Multi-criteria calibration should comprise more than two observables to further constrain the space of plausible model realizations.…”