Abstract
Abstract. Historical hydrology is based on data derived from historical written, pictorial and epigraphic documentary sources. It lies at the interface between hydrology and environmental history, using methodologies from both disciplines basically with the goal of significantly extending the instrumental measurement period with experience from the pre-instrumental past. Recently this field of research has gained increased recognition as a tool to improve current flood risk estimations when EU guidelines regulated by law the quantitative consideration of previous floods.1 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 the Environment (FOEN) to assess the magnitudes of pre-instrumental Aare River flood discharges, including the most important tributaries (the Saane, Emme, Reuss and Limmat rivers). The results of the historical hydrological study serve now as the basis for the main study, EXAR (commissioned under the lead of FOEN in cooperation with the Swiss Nuclear Safety Inspectorate (ENSI), the Swiss Federal Office of Energy (SFOE), the Federal Office for Civil Protection (FOCP), and the Federal Office of Meteorology and Climatology (MeteoSwiss)), which combines historical and climatological analysis with statistical approaches and mathematical models with the goal of better understanding the hazards and possible interactions that can be caused by extreme flood events. In a second phase the catchment of the River Rhine will be targeted as well. More recently several local historical hydrological studies of smaller catchments have been requested by the 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. 1Guideline 2007/60/EG of the European Parliament and Council from 23 October 2007 on assessment and management of flood risks, Official Journal of the European Union, L 288, 27–34, Brussels, 2007.
Highlights
This paper aims to describe the potential of historical hydrology in Switzerland in terms of data availability, methodologies, reconstruction capabilities and usefulness for the scientific and practical communities like federal or cantonal agencies and private engineering companies by adding a longerterm historical perspective to the spectrum of already existing risk and vulnerability assessments
The specific targets are (1) to describe the strengths and weaknesses of the available historical hydrological documentary evidence, (2) to shed light on the existing basic methodologies leading to long-term frequency, seasonality and magnitude reconstructions of pre-instrumental hydrological events, (3) to discuss the comparability of reconstructed pre-instrumental flood events compared to current events and (4) to provide an outlook for future analysis which might be unique to Switzerland
Prospects are good that reconstructed pre-instrumental flood magnitudes may be homogenised to actual runoff conditions, so that floods of pre-anthropogenic river engineering measures may be compared to the more recent floods under the actual anthropogenically influenced runoff conditions
Summary
This paper aims to describe the potential of historical hydrology in Switzerland in terms of data availability, methodologies, reconstruction capabilities and usefulness for the scientific and practical communities like federal or cantonal agencies and private engineering companies by adding a longerterm historical perspective to the spectrum of already existing risk and vulnerability assessments. The concept of historical hydrology is – not by its definition but by its specific application – quite often used as an equivalent to analysis of – mostly – extreme pre-instrumental or early instrumental flood events even though the research interest of historical climatology is more heterogeneous. In this paper the almost complete spectrum of historical hydrology shall be applied, meaning that all kinds of pre-instrumental hydrological events like floods or droughts as well as precedent meteorological causes of such events or the anthropogenic influence on discharge conditions are meant when the term “historical hydrology” is used. The specific targets are (1) to describe the strengths and weaknesses of the available historical hydrological documentary evidence, (2) to shed light on the existing basic methodologies leading to long-term frequency, seasonality and magnitude reconstructions of pre-instrumental hydrological events, (3) to discuss the comparability of reconstructed pre-instrumental flood events compared to current events and (4) to provide an outlook for future analysis which (in some cases) might be unique to Switzerland
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