Science and Work Plan

Organizational background

The IGCP 565 Project

The Science Issues

The key scientific issues addressed in the frame of the IGCP 565 Project in order to reach the objectives are:

  1. The development of an integrated dynamic model for the predictions of the geodetic signals of daily to interannual surface mass changes: these surface mass changes are mainly relocation of water mass in the ocean, atmosphere, and terrestrial hydrosphere. The main source of current model inaccuracies is in the surface mass models and the modeling approach, which does not sufficiently account for the mass conservation in the global water cycle and the gravitational and mechanical interactions between water mass redistribution and solid Earth deformations (Plag et al., 2007, and the references therein). Moreover, the surface mass-induced deformations and gravity signals are not sufficiently taken into account in space-geodetic analysis, leading to biases in the geodetic reference frame (Herring et al., 2007) and surface mass estimates (Kutsche and Schramma, 2006; Wu et al., 2006).
  2. Inversion algorithms for combined geodetic observations for surface mass changes: currently, most inversions for surface mass changes are based on one technique (e.g. Blewitt et al., 2001 for GPS; Crowley et al., 2006; Velicogna and Wahr, 2005 for GRACE), while combined analyses exploring the strength and mitigating the weaknesses of the individual techniques are just starting to emerge (e.g. Kusche and Schramma, 2005; Wu et al., 2006; Gross et al., 2007). Cross-validation of techniques is not explored and increase in resolution through multi-technique combinations has not been assessed. Inversion algorithms that routinely utilize multi-technique data are not available and need to be developed in order to make water-cycle related space-geodetic products continuously available. The goal of these algorithms is the determination of surface mass changes equivalent to 1 mm water column with spatial and temporal resolutions of 100 km and 10 days, respectively.
  3. Integration/assimilation of observed surface mass changes in hydrological models: models of the global water cycle are increasingly gaining in complexity, accuracy, and predictive capabilities. Most of these models are based on meteorological observations and coupled atmosphere ocean models. Examples are the Land Dynamics (LaD)World Model (Milly and Shmakin, 2002), the hydrological components of the reanalysis models of ECMWF and NCEP/NCAR, and the Global Land Data Assimilation System (GLDAS, Rodell et al., 2007). Comparisons of the terrestrial water storage predicted by these models show significant intermodel differences. Therefore, utilizing the geodetic observations of surface mass in model validation is expected to resolve some of these differences. Subsequent assimilation of the geodetic products in these models will likely help improve the accuracy and cross-model consistency.
  4. Development of products relevant for regional water management: for practical applications, estimates of changes in surface mass are not directly usable. Together with water management experts, it will be necessary to develop specific products serving the users' needs in this field. Science questions to be addressed include the relation between the surface mass changes and hydrological parameters such as changes in regional aquifer, surface water storage, and soil moisture. The goal is to develop groundwater hydrology and terrestrial surface-groundwater modeling based on space-geodetic observations of GRACE- and GPS-type.

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