|Paper title||Water height change and climate in central Europe|
|Form of presentation||Poster|
Surface water level and river discharge are key observables of the water cycle and among the most sensible indicators that integrate long-term change within a river basin. As climate change accelerates and intensifies the water cycle, streamflow monitoring allows the understanding of a broad range of science questions focused on hydrology, hydraulics, biogeochemistry, water resources management and flood protection. Streamflow change is a response to anthropogenic, as deforestation, land use change, urbanization, and natural, as climate modes, climate variability, rainfall, processes. Climate and internal drainage mechanisms affect and control, together with river discharge also lake, reservoirs, mountain glacier storage. An enhanced global warming, predicted by coupled models as due to anthropogenically-induced greenhouse warming, is expected to accelerate the current glacier decline. Moreover, precipitation cause fluvial floods, when rivers burst their banks as a result of sustained or intense rainfall, and pluvial floods, when heavy precipitation saturates drainage systems.
Change in storage and release of water is important for watershed management, including the operation of hydroelectric facilities and flood forecasting, and have direct economic effects. We analyse the observability of extremes water levels events (in low/high water and in discharge) and the long-term variability from space data for the Rhine, Elbe River catchments in central Europe. We consider for the river Rhine the extreme in July 2021 in particular.
Over the last decade, the merging of innovative space observations with in-situ data provides a denser and accurate two-dimensional observational field in space and time compared to the previous two decades, and allow to better monitor the impact of water use and characterize climate change. The new generation of space borne altimeters includes Delay Doppler, laser and bistatic SAR altimeter techniques. The central hypothesis is that these new observations outperform conventional altimetry (CA) and in-situ measurements providing (a) surface water levels and discharge of higher accuracy and resolution (both spatial and temporal), (b) new additional parameters (river slope and width) and (c) better sampling for flood event detection and long-term evolution, providing valuable new information to modelling.
In this study, radar and laser satellite altimetry and satellite images provide the space observations, radar altimeter data are processed by the GPOD ESA service. Time-series of Water Surface Elevation (WSE) are built by two methods. In the first method, time-series are built by collecting the observations of one single virtual point (one-VS), while in the second time-series are constructed from observations at multiple VS (multi-VS) after correcting for the river mean slope. The accuracy of the time-series built with both methods is 10 cm and 30 cm for Sentinel-3. The second method applied to CryoSat-2 SARIN data produces less accurate time-series and gives a similar accuracy for unfocused and fully focused (FF-SAR) processing. The impact on the results of the chosen centerline and mean river slope is investigated using the SWORD database and the national agency BfG database. The river discharge is evaluated.
In the long run, the long-term variability of the combined altimetric and in-situ water level and river discharge time-series depends on the changing climate and correlate with temperature and precipitation at basin and regional scales.
This study is part of Collaborative Research Centre funded from the German Research Foundation (DFG): “Regional Climate Change – The Role of Land Use and Water Management”, in sub-project DETECT-B01 “Impact analysis of surface water level and discharge from the new generation altimetry observations” which addresses the two research questions: (1) How can we fully exploit the new missions to derive water level, discharge, and hydrodynamic river processes, and (2) can we separate natural variability from human water use?