Indicator water

Flood events

Flood events cause major damage due to inundation. They can often endanger life and damage or destroy buildings. Foundations can be undermined by bank erosion and degradation. Debris (stones and sludge) and driftwood conveyed by the flood can damage agricultural land and buildings. On the other hand, floods also perform ecological functions, for example by regularly inundating floodplains and modifying channel morphology. Both the frequency and magnitude of flood events are closely tied to climatic changes (e.g. natural fluctuations in atmospheric circulation or warming caused by human activity).

Assessment of the state
impossible to evaluate impossible to evaluate
Assessment of the trend
impossible to evaluate impossible to evaluate
Number of flood events per year* 2018: 4 Number of flood events per year* 2017: 4 Number of flood events per year* 2016: 7 Number of flood events per year* 2015: 7 Number of flood events per year* 2014: 13 Number of flood events per year* 2013: 9 Number of flood events per year* 2012: 6 Number of flood events per year* 2011: 15 Number of flood events per year* 2010: 6 Number of flood events per year* 2009: 1.96923076923077 Number of flood events per year* 2008: 7.87692307692308 Number of flood events per year* 2007: 25.6 Number of flood events per year* 2006: 7.87692307692308 Number of flood events per year* 2005: 27.5692307692308 Number of flood events per year* 2004: 7 Number of flood events per year* 2003: 1 Number of flood events per year* 2002: 13 Number of flood events per year* 2001: 2.95384615384615 Number of flood events per year* 2000: 8.86153846153846 Number of flood events per year* 1999: 16.7384615384615 Number of flood events per year* 1998: 4.92307692307692 Number of flood events per year* 1997: 8.86153846153846 Number of flood events per year* 1996: 1.96923076923077 Number of flood events per year* 1995: 7.87692307692308 Number of flood events per year* 1994: 6 Number of flood events per year* 1993: 4 Number of flood events per year* 1992: 3.93846153846154 Number of flood events per year* 1991: 4.92307692307692 Number of flood events per year* 1990: 9.84615384615385 Number of flood events per year* 1989: 1.96923076923077 Number of flood events per year* 1988: 8 Number of flood events per year* 1987: 16 Number of flood events per year* 1986: 3 Number of flood events per year* 1985: 5 Number of flood events per year* 1984: 9.14285714285714 Number of flood events per year* 1983: 5.16129032258065 Number of flood events per year* 1982: 10.1587301587302 Number of flood events per year* 1981: 4 Number of flood events per year* 1980: 3.04761904761905 Number of flood events per year* 1979: 0 Number of flood events per year* 1978: 12.3870967741935 Number of flood events per year* 1977: 18.8852459016393 Number of flood events per year* 1976: 3.14754098360656 Number of flood events per year* 1975: 7.2258064516129 Number of flood events per year* 1974: 5.07936507936508 Number of flood events per year* 1973: 4.06349206349206 Number of flood events per year* 1972: 4.06349206349206 Number of flood events per year* 1971: 4.19672131147541 Number of flood events per year* 1970: 7.34426229508197 Number of flood events per year* 1969: 1.01587301587302 Number of flood events per year* 1968: 10.1587301587302 Number of flood events per year* 1967: 0 Number of flood events per year* 1966: 5.24590163934426 Number of flood events per year* 1965: 6.73684210526316 Number of flood events per year* 1964: 1.08474576271186 Number of flood events per year* 1963: 2.16949152542373 Number of flood events per year* 1962: 2.24561403508772 Number of flood events per year* 1961: 0 Number of flood events per year* 1960: 7.24528301886792 Number of flood events per year* 1959: 0 Number of flood events per year* 1958: 6.27450980392157 Number of flood events per year* 1957: 9.14285714285714 Number of flood events per year* 1956: 6.53061224489796 Number of flood events per year* 1955: 5.4468085106383 Number of flood events per year* 1954: 18.0869565217391 Number of flood events per year* 1953: 9.95555555555556 Number of flood events per year* 1952: 0 Number of flood events per year* 1951: 2.90909090909091 Number of flood events per year* 1950: 5.81818181818182 Number of flood events per year* 1949: 1.52380952380952 Number of flood events per year* 1948: 18.7317073170732 Number of flood events per year* 1947: 0 Number of flood events per year* 1946: 6.24390243902439 Number of flood events per year* 1945: 0 Number of flood events per year* 1944: 17.1707317073171 Number of flood events per year* 1943: 1.5609756097561 Number of flood events per year* 1942: 1.5609756097561 Number of flood events per year* 1941: 1.5609756097561 Number of flood events per year* 1940: 6.24390243902439 Number of flood events per year* 1939: 12.4878048780488 Number of flood events per year* 1938: 10.9268292682927 Number of flood events per year* 1937: 1.5609756097561 Number of flood events per year* 1936: 4.68292682926829 Number of flood events per year* 1935: 9.6 Number of flood events per year* 1934: 3.28205128205128 Number of flood events per year* 1933: 0 Number of flood events per year* 1932: 0 Number of flood events per year* 1931: 0 Number of flood events per year* 1930: 0
* Measured at 64 stations chosen among FOEN discharge measurement stations

Data for the graph: Excel
Source: Federal Office for the Environment
Comment

An evaluation of the annual peak discharge data since 1930 shows that the frequency of flooding has been rising since the mid-1970s, with an above-average number of flood events observed during the past 30 years. The three most severe flood events since 1930 all occurred between 1999 and 2018. By contrast, there were only very few flood events between 1960 and 1975. Over the past 500 years, climatic changes (such as fluctuations in atmospheric circulation) have caused repeated alternation between phases with many and few flood events. It is not yet possible to conclusively determine whether the increase in the number and magnitude of flood events observed since the 1970s is already a consequence of human-induced climate warming, and in view of this the indicator is not evaluated.

There is no absolute protection against extreme events. The most efficient way to avoid flood damage is to adapt land use in order to prevent development in areas that are susceptible to flooding. Where this is not possible, structural or organisational measures have to be taken in order to lessen the risk or reduce the potential for damage.

International comparison

The “CLIM17 – River floods” indicator of the European Environment Agency presents the sum of flood events over the period from 1998 to 2008 for various European river basins. While the Swiss indicator shows the development of flood frequency over time, the European indicator shows the spatial differences.

Method

The peak discharges (highest discharge in a given year) are measured at each of the 64 permanent Federal Office for the Environment discharge measurement stations for each year and each station. An annual peak discharge is defined as a flood event if its flow rate is greater than the HQ10 flow calculated for the station (HQ10 flow = discharge that is exceeded statistically every 10 years). The indicator shows the total of all flood events per annum at the 64 stations.

 
Last updated on: 20.04.2021

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