Hydrograv - Improving Hydrological Models with Ground-Based and Space-Borne Time-lapse Gravity Surveys
Bauer-Gottwein, P.1; Andersen, O.2; Leiriao, S.1; He, X.1
1Technical University of Denmark; 2Danish National Space Center

Space-borne and ground-based time-lapse gravity observations provide new data for hydrological model calibration. The Hydrograv project ( will explore the utility of time-lapse gravity surveys for hydrological model calibration in two target regions, the island of Zealand in Denmark and the Okavango Delta region in Botswana, Southern Africa.

The hydrology-induced changes in the gravitational acceleration can be forward calculated from the output of integrated hydrological models. Hydrological models (e.g. MIKE SHE, MODFLOW) provide water storage output that is discretized in time and space. The total gravity change on the ground or in space can be calculated as the sum of the incremental gravity changes produced by storage changes in the individual grid cells of the hydrological model (instead of the common infinite sheet approximation).

Forward gravity calculation from hydrological model output is the basis for model calibration using gravity data. All hydrological models use a number of uncertain input parameters and gravity observations, along with traditional hydrological observations such as discharge, soil moisture and groundwater levels, can be used to condition uncertain input parameters and thus increase model reliability and predictive capability.

First results of forward gravity calculation from a hydrological model of Northern Zealand indicate hydrology-induced gravity changes on the order of several tens of microgals.


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