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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 new 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.
Braunsbach and nearby villages suffered losses of €104 million as a result. A task force of the Research Training Group "Natural Hazards and Risks in a Changing World" ("NatRiskChange") at the University of Potsdam investigated the event thoroughly. Under the project P1 "Landslide Prediction under Changing Boundary Conditions", we studied the geomorphic legacy of this particular flash flood in the moderate-relief cuesta landscape of southern Germany. Flash floods and debris flows are iconic hazards in mountainous regions with steep relief, high rainfall intensities, rapid snowmelt events, and ample sediments. The cuesta landscapes of southern Germany hardly come to mind when dealing with such hazards. Flash floods in humid areas with more moderate relief are usually less hazardous, but may cause substantial harm due to largely eroded public awareness, which is inversely linked to the interval between the subsequent localized incidents. The reported historic flash flood within 5 km distance to Braunsbach is in fact an evidence for recurring flash floods and debris flows in the nearby region. In the picture we see that large amounts of debris destroyed houses and buried streets in Cröffelbach in 1927 (Brigitte Blum-Karsch, pers. comm., 2016), which is comparable to the recent incident in Braunsbach. In addition, the bank of the Orlacher Bach was reinforced around 1903 by Swiss mountain engineers (Andreas Ilg, pers. comm, 2017), which hints at a once experienced or perceived danger that might be related to an incident even before the 1927 flood. Unfortunately the old river-bed construction was eroded to large extents during the recent flash flood and contributed to the amount of mobilized gravel.
We try to develop robust methods and algorithms for predicting the timing and location of landslides under non-stationary boundary conditions within the project P1 “Landslide Prediction under Changing Boundary Conditions”. Thus, understanding the mechanism of Braunsbach-like unexpected events is particularly important in order to achieve the goal of the Project P1.
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!