Das Projekt "The effect of water storage variations on in-situ gravity measurements and their use for hydrology (HYGRA)" wird vom Umweltbundesamt gefördert und von Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum durchgeführt. Water storage variations in the soil, groundwater, snow cover and in surface water bodies cause a gravitational effect due to mass attraction. Thus, there exists a strong interrelation between hydrology and gravity. From a hydrological perspective, the estimation of water storage and its spatio-temporal changes is essential for setting up water balances and for effective water use and management. However, direct measurements of local water storage changes are still a challenging task while time-variable gravity observations are a promising tool as an integrative measure of total water storage changes. From a geodetic perspective, the hydrological gravity effect is an interfering signal, which imposes noise on gravimetric measurements and thus has to be eliminated from the gravity records. Superconducting gravimeters (SG) enable the in situ observation of the temporal changes of the earth gravity field. These SG data contain information about polar motion, earth tides, oscillations of the earth, atmospheric pressure and hydrology. But still variations in local water masses have a significant influence on SG measurements. Hence, the question is: How does local water storage change influence the signal of SG measurements? Objective: The objective of the HYGRA project is to separate the local hydrological signal from the integral signal of the SG records. From the geodetic perspective, this will provide a tool to remove the unwanted hydrological noise in SG recordings. At the same time, the hydrological gravity signal bears the potential to estimate hydrological state variables (ground water, soil moisture). Study Area: The HYGRA project focuses the relation of local hydrology and gravity in following study areas: Geodätisches Observatorium Wettzell, Deutschland; South African Geodynamic Observatory (SAGOS). Method The investigation of the interrelation between hydrology and geodesy is done by following worksteps: 1. 4D Simulation of the influence of water storage changes on the superconducting gravimeter; 2. Measuring and modelling of the different water storages; namely groundwater, soil moisture and snow; 3. Transformation of the water storage changes to a gravimetric signal; 4. Comparison between the measured gravity change by the SG and the estimated hydrological gravity response.