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Flood regimes along the Rhine river appear to be changing. In the last decades, some snow-melt dominatedfloods have occured relatively early in the year, for example in the Pentecost flood in 1999. In tributary riversfurther north, where floods mostly stem from long rainfall events, extreme streamflow levels seem to beincreasing. If these trends continue into the future, there may be a temporal overlap in snow and rain floods,which may bring larger floods than ever in the middle Rhine. This is the region where both regimes mix but,up to now, produce their large floods in distinctly separate seasons.
The PhD project attempts to answer three main questions:
The historical observations have been analyzed by Berry Boessenkool, while the modelling part will be tackledby Erwin Rottler starting 2018.Berry Boessenkool has collected and combined daily streamflow values from 196 gauges. He developedmethods to visualize seasonality of time series as well as changes in the timing of extreme values, all wrapped in a documented R package .
The front graph shows one of the visualizations of seasonality changes for the Rekingen gauge in theHigh Rhine just before the Aare enters the Rhine from the south. This streamflow gauge captures a mainlyalpine regime with floods dominated by snow melt in the summer season. For each day of the year (DOY) inthose periods, return levels are computed that describe the streamflow value that is expected to occur every 2or 50 years (a normal and high flood). To discern changes over time, the time series has first been split up in30-year periods as displayed in the topright legend. At the gauges in this part of the Rhine river, the highfloods occur increasingly early in the year.
The change in timing of snow melt floods in the last decades can also be shown (more effectively than in thefront graph) with the graph below, where crosses mark the annual maxima of the threshold exceedances.
Berry Boessenkool & Erwin Rottler
In the wake of changing hydro-climatological, geo-physical and socio-economic conditions the magnitude, frequency and impact of certain types of natural hazards are likely bound to change as well. This is highly of utmost importance for many regions in the world where risks due to natural hazards have to be managed and mitigated and this is where the research training group “Natural hazards and risks in a changing world (NatRiskChange)” aims to foster the scientific knowledge basis. This research training group started on October 1st 2015 and is funded by the Deutsche Forschungsgemeinschaft DFG. The central goal of NatRiskChange is to pursue the development of methods to improve hazard and risk analysis and quantification based on the transient, non-stationary nature of hazards and risks in response to changing natural and anthropogenically altered components of the Earth system. Key scientific aims are the development, testing, and pilot application of studies on identification, quantification (mechanisms) and prediction of transient natural hazards and associated risks.
Within NatRiskChange, a telephone aided survey was conducted in October and November 2017 among companies, which were affected from heavy rainfall or flash flood events in 2014 to 2016. We aim at gathering information about the companies experiences with severe weather warning systems, the type and extent of the damage as well es the state of recovery. Results shall identify improved mitigation measures for the management of eavy rainfall events. We thank all participants of the survey for their support!