Global lakes and reservoirs: An investigation to which extent dynamic water body shapes have an impact on the estimates of the total water storage derived from GRACE

The satellite mission Gravity Recovery and Climate Experiment (GRACE) measures gravity field variations caused by mass redistributions across the atmosphere, the continents and the oceans. Since the redistributions over the continents are linked to changes in the total water storage (TWS), expressed as equivalent water heights (EWH), the observations can be used to quantitatively assess global freshwater variations, which is of great social importance in times of increasingly scarce water resources. If the focus of interest refers to groundwater related variations explicitly, all other storage compartments (here: surface waters) have to be reduced from the GRACE observations. Therefore, the retrieved signal has to be decomposed into its individual components. To achieve this, the water volume can be estimated by forward modelling satellite altimetry and remote sensing data, considering both static and dynamic surface expansions. It will be discussed, that using a dynamic instead of a static surface area extent (1) will change the equivalent water height values in a magnitude between 0.006 cm and 0.243 cm, (2) causes the largest deviation for the Lake Mead and (3) that the question whether a dynamic or a static water body shape should be considered is driven by the interaction of various parameters.