The Potential of Historical Hydrology in Switzerland

Historical hydrology bases on data derived from historical written-, pictorial and epigraphic documentary sources. It lies on the interface between hydrology and environmental history using methodologies from both disciplines basically with the goal to significantly extend the instrumental measurement period with the experience from the pre instrumental past. Recently this field of research gained some recognition as a tool to improve current flood risk estimations when EU guidelines regulated by law the quantitative consideration of previous floods. The awareness to consider pre instrumental experience in flood risk analysis seems to have risen at the level of local- and federal authorities in Switzerland as well. The 2011 Fukushima catastrophe probably fostered this rethinking process, when pressure from the media, society and politics as well as the regulations of the International Atomic Energy Agency (IAEA), forced the authorities to reassess the current flood risk analysis for Swiss nuclear power plants. In 2015 a historical hydrological study was commissioned by the Federal Office for Environment (FOEN) to assess the magnitudes of pre instrumental Aare river flood discharges including the most important tributaries (Saane-, Emme-, Reuss and Limmat river). The results of the mentioned historical hydrological study serve now as basis for the currently running main study EXAR [commissioned under the lead of FOEN in cooperation with the Swiss Nuclear Safety Inspectorate (ENSI), Swiss Federal Office of Energy (SFOE), Federal Office for civil protection (FOCP), Federal Office of Meteorology and Climatology (MeteoSwiss)] which combines historical- and climatological analysis with statistical approaches and mathematical models with the goal to better understand the hazards and possible interactions that can be caused by extreme flood events. In a second phase the catchment of Rhine River will be targeted as well. More recently several local historical hydrological studies of smaller catchments have been requested by responsible local authorities. The course for further publicly requested historical hydrological analysis seems thus to have been set. This paper therefore intends to discuss the potential of historical hydrological analysis with a focus on the specific situation in Switzerland.