Hydrological Mass Variations due to Extreme Weather Conditions in Central Europe from GRACE 4-D Wavelet Expansions
Seitz, F.1; Schmidt, M.2; Shum, C.K.3; Chen, Y.3
1TU Muenchen; 2Deutsches Geodätisches Forschungsinstitut (DGFI); 3Geodetic Science, The Ohio State University
During the last five years weather conditions in Central Europe featured strong fluctuations. Heatwaves, droughts, exceptional rain, snowfall, and floodings occurred at frequent intervals. Such phenomena are associated with hydrological mass variations that are reflected by changes of the gravity field. This way they influence observations of the satellite gravity field misson GRACE over multiple seasonal scales.
Here we perform a regional analysis of GRACE data over Europe. Our approach is alternative to global spherical harmonic expansions which are routinely computed from GRACE data for fixed time intervals like one month. Since the Earth's gravity field shows heterogeneous structures over the globe, a multi-resolution representation (MRR) based on spherical wavelets means an appropriate alternative modeling candidate. The basic idea of the MRR is to split a given input signal, here the geopotential of the Earth, into a smoother version and a number of (resolution) level-dependent detail signals by successive low-pass filtering.
Resulting gravity field variations are expressed in terms of equivalent water mass which are subsequently balanced with the net effect of precipitation and evaporation (inflow) and river runoff (outflow) for seven Central European river basins. The inflow is computed from vertically integrated flux of water vapor based on atmospheric reanalysis data. Furthermore our results are compared with monthly mass grids from GRACE spherical harmonic solutions.