Changes in flood frequencies in Switzerland since 1500

Abstract

In northern Switzerland, an accumulation of large flood events has occurred since the 1970s, preceded by a prolonged period with few floods (Schmocker-Fackel and Naef, 2010). How have Swiss flood frequencies changed over the past 500 years? And how does the recent increase in flood frequencies compare with other periods in this half millennium? We collected historical flood data for 14 Swiss catchments dating back to 1500 AC. All catchments experienced marked fluctuations in flood frequencies, and we were able to identify four periods of frequent flooding in northern Switzerland, lasting between 30 and 100 years (1560–1590, 1740–1790, 1820–1940 and since 1970). The current period of increased flood frequencies has not yet exceeded those observed in the past. We tested whether the flood frequency fluctuation could be explained with generalised climatic indices like solar activity or the NAO. The first three periods of low flood frequency in Switzerland correspond to periods of low solar activity. However, after 1810 no relationship between solar activity and flood frequency was found, nor could a relationship be established between reconstructed NAO indices or reconstructed Swiss temperatures. We found re-occurring spatial patterns of flood frequencies on a European scale, with the Swiss periods of frequent flooding often in phase with those in the Czech Republic, Italy and Spain and less often with those in Germany. The pattern of flooding in northern Switzerland and the Czech Republic seem to be rather similar, although the individual flood events do not match. This comparison of flooding patterns in different European countries suggests that changes in large scale atmospheric circulation are responsible for the flood frequency fluctuations

Documentary evidence of historical floods and extreme rainfall events in Sweden 1400–1800

“…For example, both Brázdil et al (1999) and Schmocker-Fackel and Naef (2010) found few floods in northern Switzerland in the first half of the 16th century but there was a flood frequency peak in 1560-1590, whereas a first peak in Sweden is found only in the following 2 decades. As for the 17th century, there was a low in Switzer-land until the first decades of the 18th century (Pfister, 1999;Schmocker-Fackel and Naef, 2010). The latter half of the century was again a period of high frequency, which only partially coincides with the documentary data from Sweden.…”

“…Wetter et al, 2011;Benito et al, 2003;Glaser et al, 2010;Glaser and Stangl, 2004;Elleder, 2013;De Kraker, 2006). For example, both Brázdil et al (1999) and Schmocker-Fackel and Naef (2010) found few floods in northern Switzerland in the first half of the 16th century but there was a flood frequency peak in 1560-1590, whereas a first peak in Sweden is found only in the following 2 decades. As for the 17th century, there was a low in Switzer-land until the first decades of the 18th century (Pfister, 1999;Schmocker-Fackel and Naef, 2010).…”

“…In a number of studies the great variability in flood frequencies in Europe has been explained by large-scale atmospheric circulation patterns, particularly on a decadal timescale (Schmocker-Fackel and Naef, 2010;Casanueva et al, 2014). In particular, the NAO together with other, related atmospheric circulation patterns is normally seen as the main explanation for climatic variability in northern Europe (Lindholm et al, 2009), especially winter precipitation in the NAO positive phases (Hurrell and Van Loon, 1997;Barker et al, 2004;Casanueva et al, 2014) as well as for river discharges, snow accumulation and flooding (Prudhomme and Genevier, 2011).…”

Multi-scale event synchronization analysis for unravelling climate processes: a wavelet-based approach

“…Synchronization is a widespread phenomenon that can be observed in numerous climate-related processes, such as synchronized climate changes in the northern and southern polar regions (Rial, 2012), see-saw relationships between monsoon systems (Eroglu et al, 2016), or coherent fluctuations in flood activity across regions (Schmocker-Fackel and Naef, 2010) and among El Niño and the Indian summer monsoon (Maraun and Kurths, 2005;Mokhov et al, 2011). Synchronous occurrences of climate-related events can be of great societal relevance.…”

The occurrence of floods and the role of climate variations from 1880 in Calabria (Southern Italy)

“…This approach has two main purposes: (a) to obtain data concerning rivers or torrents that lack instrumental data; and (b) to expand the observation period of instrumented rivers to the pre-measurement epoch, to improve the assessment of flood recurrence and trend Herget and Meurs, 2010;Schmocker-Fackel and Naef, 2010). In cases where the river flow is extremely variable, discontinuous or sporadic, as widely observed in many Mediterranean areas and other world regions, the time series of river discharge yield or water height are generally unavailable for long periods and/or large areas.…”