1. A system comprising: a database that stores geodetic data associated with a geographic region, the geodetic data including surface gradient information for at least a subset of a plurality of surface locations in the geographic region, wherein the geodetic data comprise surface elevation information for a first subset of the surface locations and surface gradient information for a second subset of the surface locations; and a processor operable to perform operations including: generating a set of constraining relationships based on the geodetic data, the set of constraining relationships relates undetermined values for temporal changes in surface gradients at the first subset of surface locations and undetermined values for temporal changes in surface elevations at the second subset of surface locations to the surface elevation information and the surface gradient information included in the geodetic data, a plurality of the constraining relationships each include multiple undetermined values for multiple surface elevations; and identifying particular values for temporal changes in surface elevations at each surface location in the subset comprises identifying particular values for temporal changes in surface gradients for each of the first subset of locations and particular values for temporal changes in surface elevation each of the second subset of surface locations based on determining a solution to the set of constraining relationships.