Assimilation of snow melt information from SAR in the water balance and runoff model PROMET

Observation of snow cover dynamics for hydrological services can be considered as an operational task and provided routinely to water management offices world wide. Information on the snow cover extent or the fractional snow cover is used in order to validate, control and optimize the applied water balance models and snow water equivalent simulations.

Such snow services are for example provided within the GMES (Global Monitoring of Environment and Security) project PolarView that is funded by the European Space Agency and the European Commission. In the frame of Polar View, VISTA is in charge for the ‘Snow Cover Service Central Europe’ and provides snow products for the Alpine Region and Southern Germany with spatial resolutions of 1 km. Both, optical and SAR sensor are used as input data sources for the derivation of snow cover extents. Users of the service are the flood forecasts centers for the Rhine, Neckar and Mosel and the German Weather Service DWD.

The snow service developed is not limited to the observation of the snow cover; it additionally provides snow water equivalent estimates. These estimates are not directly derived from Earth Observation but retrieved from data assimilation of the EO products in water balance and snow cover simulations. As hydrological tool the PROMET-model is applied for this task.
PROMET is a physically based water balance and runoff model developed at the University of Munich. The snow-submodule of PROMET has been widely enhanced in the course of the integrative research project GLOWA-DANUBE. The goal of this project is to provide a decision support system for the assessment of the impact of global change on the water system of the Upper Danube catchment. This catchment also serves as investigation area for this study.

Data assimilation using information on snow covered area is already used in operational hydrological services to control and update spatial model calculations. Up to now snow cover products from SAR data are prepared and used in the same way as products from optical sensors. However dedicated observations on melt processes that are possible from SAR, since SAR detects wet snow, were not yet used in the data assimilation. Therefore a new data assimilation concept was developed that allows the adjustment of the snow melt process in PROMET according to the snow melt observation from SAR. It will be analyzed which impact the data assimilation has on the simulated snow water equivalent as well on the runoff in the catchment. Validation will be given comparing simulated and observed runoff in order to assess the targeted improvement of hydrological modeling using the snow melt information from SAR.