Hydrological induced Earth rotation variations from stand-alone and dynamically coupled simulations

The impact of continental water mass redistributions on Earth rotation is deduced from stand-alone runs with the Hydrological Discharge Model (HDM) forced by ERA40 re-analyses as well as by the unconstrained atmospheric climate model ECHAM5. The HDM is attached in three different approaches to the atmospheric forcing models. First, ECHAM5 and its embedded land surface model generates directly runoff and drainage appropriate for the subsequent processing with HDM, like it is realized in the dynamically coupled model system ECOCTH, too. Second, an intermediate Simplified Land Surface scheme (SLS) is used to separate ERA40 precipitation into runoff, drainage, and evaporation. Third, precipitation and evaporation are used as input for the Land Surface Discharge Model (LSDM), which estimates runoff and drainage internally for its HDM-like discharge scheme. The individual models are validated by observed river discharges. The induced rotational variations represent mainly the different forcing from precipitation-evaporation and trends from inconsistent mass fluxes. The dynamical coupling of atmosphere and ocean has only a subordinated influence.