Extreme River Floods in Western Switzerland and the Lake of Constance Region in the Period Prior to Instrumental Measurements

The floods that occurred on the Aare and Rhine rivers in May 2015 and the mostly successful handling of this event in terms of flood protection measures are a good reminder of how important it is to comprehend the causes and processes involved in such natural hazards. While the needed data series of gauge measurements and peak discharge calculations reach back to the 19th century, historical records dating further back in time can provide additional and useful information to help understanding extreme flood events and to evaluate prevention measures such as river dams and corrections undertaken prior to instrumental measurements. In my PhD project I will use a wide range of historical sources to assess and quantify past extreme flood events. It is part of the SNF-funded project “Reconstruction of the Genesis, Process and Impact of Major Pre-instrumental Flood Events of Major Swiss Rivers Including a Peak Discharge Quantification” and will cover the research locations Fribourg (Saane R.), Burgdorf (Emme R.), Thun, Bern (both Aare R.), and the Lake of Constance at the locations Lindau, Constance and Rorschach. My main goals are to provide a long time series of quantitative data for extreme flood events, to discuss the occurring changes in these data, and to evaluate the impact of the aforementioned human influences on the drainage system. Extracting information given in account books from the towns of Basel and Solothurn may also enable me to assess the frequency and seasonality of less severe river floods. Finally, historical information will be used for remodeling the historical hydrological regime to homogenize the historical data series to modern day conditions and thus make it comparable to the data provided by instrumental measurements. The method I will apply for processing all information provided by historical sources such as chronicles, newspapers, institutional records, as well as flood marks, paintings and archeological evidence has been developed and successfully applied to the site of Basel by Wetter et al. (2011). They have also shown that data homogenization is possible by reconstructing previous stream flow conditions using historical river profiles and by carefully observing and re-constructing human changes of the river bed and its surroundings. Taken all information into account, peak discharges for past extreme flood events will be calculated with a one-dimensional hydrological model.

A 2000 year long seasonal record of floods in Lake Ledro

Knowledge of past natural flood variability and controlling climate factors is of high value since it can be useful to refine projections of the future flood behavior under climate warming. In this context, we present a seasonally resolved 2000 year long flood frequency and intensity reconstruction from the southern Alpine slope (North Italy) using annually laminated (varved) lake sediments. Floods occurred predominantly during summer and autumn, whereas winter and spring events were rare. The all-season flood frequency and, particularly, the occurrence of summer events increased during solar minima, suggesting solar-induced circulation changes resembling negative conditions of the North Atlantic Oscillation as controlling atmospheric mechanism. Furthermore, the most extreme autumn events occurred during a period of warm Mediterranean sea surface temperature. Interpreting these results in regard to present climate change, our data set proposes for a warming scenario, a decrease in summer floods, but an increase in the intensity of autumn floods at the South-Alpine slope.

Survey on economic assessment of the improvement of the quality of environment: the case of the fight against floods in Cotonou (Benin Living Standard Survey)

This study aims to analyze households' attitude toward flood risk in Cotonou in the sense to identify whether they are willing or not to leave the flood-prone zones. Moreover, the attitudes toward the management of wastes and dirty water are analyzed. The data used in this study were obtained from two sources: the survey implemented during March 2011 on one hundred and fifty randomly selected households living in flood-prone areas of Cotonou, and Benin Living Standard Survey of 2006 (Part relative to Cotonou on 1,586 households). Moreover, climate data were used in this study. Multinomial probability model is used for the econometric analysis of the attitude toward flood risk. While the attitudes toward the management of wastes and dirty water are analyzed through a simple logit. The results show that 55.3% of households agreed to go elsewhere while 44.7% refused [we are better-off here (10.67%), due to the proximity of the activities (19.33), the best way is to build infrastructures that will protect against flood and family house (14.67%)]. The authorities have to rethink an alternative policy to what they have been doing such as building socio-economic houses outside Cotonou and propose to the households that are living the areas prone to inundation. Moreover, access to formal education has to be reinforced.

Advanced methodologies for the dendrogeomorphic analysis of past floods and related risks

This communication presents an overview of their first results and innovate methodologies, focused in their possibilities and limitations for the reconstruction of recent floods and paleofloods over the World.

Correlating a documentary record of historical floods with the dendrochronological dating of a wooden decking in the old mint of Segovia (Spain)

the aim of this study is to apply an integrated methodological approximation where dendrochronology and documentary analysis allow us to reconstruct the historical flood record of the Segovia Mint. Our hypothesis is that differences between the dendrochronological data of the wooden decking pieces can be related to historical floods and, therefore, they could be used as proxy-source data in future palaeoflood research.

Meteocean Influence on Inland and Coastal Floods in the East of Spain

The Santa Irene flood, at the end of October 1982, is one of the most dramatically and widely reported flood events in Spain. Its renown is mainly attributable to the collapse of the Tous dam, but its main message is to be the paradigm of the incidence of the maritime/littoral weather and its temporal sea-level rise on the coastal plains inland floods. The Santa Irene flood was attributable to a meteorological phenomenon known as gota fría (cold drop), a relatively frequent and intense rainy phenomenon on the Iberian Peninsula, particularly on the Spanish E to SE inlands and coasts. There are some circumstances that can easily come together to unleash the cold drop there: cold and dry polar air masses coming onto the whole Iberian Peninsula and the north of Africa, high sea-water temperatures, and low atmospheric pressure (cyclone) areas in the western Mediterranean basin; these circumstances are quite common during the autumn and, as it happens, in other places around the world (E/SE Africa). Their occurrence, however, shows a great space-temporal variability (in a similar way to hurricanes on Caribbean and western North Atlantic areas or also in a similar way to typhoons). In fact, all of these are equivalent, although different, phenomena, able to have a different magnitude each time. This paper describes the results of a detailed analysis and reflection about this cold drop phenomenon as a whole, on the generation of its rains, and on the different natures and consequences of its flood. This paper also explains the ways in which the nearby maritime weather and the consequential sea level govern floods on different zones of any hydrographical basin. The Santa Irene case can be considered as a paradigm to explain the influence of nearby maritime climatic conditions on flooding phenomena not only in coastal but also in upward inland areas.