The following maps depict precipitation amounts for extreme events. The spatially comprehensive representation describes the climate of heavy precipitation in Switzerland and illustrates contrasts between regions and seasons. The maps constitute an important knowledge base for the protection against natural hazards.
Maps of extreme precipitation
The graphics represent return levels as a function of return period T. A return level quantifies the amount of precipitation that, in today’s climate and at the location of interest, is exceeded with a probability of 1/T in one year. Additional graphics represent the uncertainty of the estimated return levels. At present, this site depicts results for precipitation sums over the duration of one day.
The analyses were derived from precipitation measurements at 360 stations in Switzerland in the period 1961-2014. In an upcoming update, measurements from more recent years and from the bordering countries will also be integrated. The depicted return levels of extreme precipitation are valid at the point scale. Note that colour scales vary between maps for different return periods.
100-year return level of 1-day precipitation sums
The map shows, for each location in Switzerland, the precipitation sum (accumulations over one day) that is exceeded at the respective location with a probability of 0.01 (1/100) in one year. In a stationary climate under present-day conditions, the depicted values (or larger amounts) are expected only once in 100 years on average. Regional variations are very large. At the valley floor of Valais the 100-year return level is less than 100 mm, while over large parts of western Ticino, the same statistic is larger than 300 mm.
A consequence of the limited measurement period and spatial interpolation is the rather large uncertainty in the estimates of the 100-year return levels. In regions with a dense measurement network (e.g. the upper lake Zürich) the uncertainty is less than 15%, while it amounts to more than 20% in high-mountain regions close to the country border (e.g. the southern parts of Valais).