Effects of Continental Water Mass Distribution on Geophysical Processes

Temporal variations in the global distribution of water storage on the continents have long been a source of “noise” in analyses of many non-hydrologic processes. Geodetic and gravimetric surveys (and related global positioning and navigational systems) must contend with time-varying water-load-induced deformations of the land surface and fluctuations in the gravitational pull of transient water masses. Global dynamic parameters, such as the length of day and changes in oblateness of the Earth, are also affected.

We have initiated a program of retrospective simulations (“LaDWorld”) of global continental water storage. The first “LaDWorld” was reported by Shmakin et al. (2002, abstract, paper), and subsequent versions have been shared with interested parties. We have recently extended simulations halfway through 2003, creating temporal overlap with observations of the recently launched Gravity Recovery and Climate Experiment (GRACE).

Science results based on the LaDWorld product have appeared recently. Vertical crustal deformations computed from LaDWorld mass loadings successfully reproduce much of the observed signal from a network of Global-Positioning-System (GPS) ground stations (van Dam et al., 2001a, abstract, paper). We have used LaDWorld data to estimate gravitational effects of water mass loading (van Dam et al., 2001b) and to evaluate, in an a priori mode, the error characteristics of the GRACE mission (Swenson et al., 2003, abstract, paper), and the GRACE Science Team is using them to evaluate, a posteriori, the performance of the GRACE data systems. Milly et al. (2003, abstract) have used LaDWorld results to infer that an ocean-land “see-saw” of water storage contributes substantially to observed seasonal-to-interannual variations in global mean sea level. 

LaDWorld data have been supplied, in response to requests, to research groups at NASA Goddard Space Flight Center, NASA Marshall Space Flight Center, NASA Jet Propulsion Lab, Lawrence Livermore National Lab, Centre National d’Etudes Spatiales (National Center for Space Studies, France), Centre d’Etudes Spatiales de la Biosphere (Center for Remote Sensing of the Biosphere, France), Instituto Nacional do Pesquisas Espaciais (National Institute for Space Research, Brazil), GeoForschungsZentrum Potsdam (geoscientific research institute, Germany), Univ. Bourgogne (France), Univ. Strasbourg (France), Univ. Texas Austin, Univ. Colorado, La Plata Univ (Argentina), Technische Universität München (Germany), and European Center for Geodynamics and Seismology (Luxembourg).

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