Extreme Rainfalls in Switzerland in 2005
Summary of the events
The 21st and 22nd of August 2005 will stay in the annals of Switzerland. Bad weather led to numerous floods and landslides across the country, particularly in central Switzerland like “Obwald” canton. The estimated loss of 2.5 billion Swiss francs and six deaths were to deplore. To help people, “la chaine du bonheur” collected and transferred 39.5 million CHF for various individuals (companies and private people) in mountain areas [5].
Cumulating the rainfall of the two days, this was a centennial event. In the municipality of Weesen (SG), the recorded precipitation reached 270.2 mm in 48 hours. The recurrence of events of this magnitude depends on the interpretation of the measurements at 26 different stations and on the level of knowledge available. In 2005, some localities considered this event as a historical record, thought to occur only every 1’000 years. Nowadays, this event is considered centennial because the measurements varied depending on the location of the survey station [4].
Origins and predictions
The winds brought mild, moisture-laden air north of the Alps and a climatic barrage kept the precipitations over the same area for an extended period (fig. 1) [3].
Even if the atmospheric conditions were special, they were relatively forecasted. COSMO-LEPS is a simulation software which predicts the probability of occurrence of several meteorological scenarios, according to the accumulation of precipitation over a 3-day period. Thus, it allows to evaluate the potential dangers linked to extreme climatic events. In this case, for the dates of August 21 and 22, 2005, the software estimated the events with a probability rate of 30% for events of more than 150 millimetres (fig. 2). In any case, it was clear that this would be a particular event and that the probabilities increased as the simulation got closer in time to the event they had to predict [2].
Improvements
Following these events, the Confederation decided to react. It constituted a pole of competences around the natural hazards, those generated by extreme meteorological events.The system of communication and responsibility between “Météosuisse” and other stakeholders was therefore rethought and improved. “MétéoSuisse” now has at its disposal a finer network of survey stations and more advanced tools for communication and accountability between “MétéoSuisse” and other stakeholders as well as more advanced resources for meteorological simulations. On the other hand, the federal and cantonal authorities have standardized the warning procedure for the population and have also adjusted communication and the sharing information. One of the innovations resulting from these adjustments is the warnings system offered by the mobile application named : “MétéoSuisse”. [1]
References :
[1] « Amélioration des avertissements et de la collaboration entre les autorités – MétéoSuisse ». Consulté le 6 janvier 2021. https://www.meteosuisse.admin.ch/home/actualite/infos/intemperies-d-aout-2005-un-evenement-record-avec-des-consequences/amelioration-des-avertissements-et-de-la-collaboration-entre-les-autorites.html.
[2] « COSMO-LEPS : prévision précoce d’un épisode de précipitations extrêmes – MétéoSuisse ». Consulté le 6 janvier 2021. https://www.meteosuisse.admin.ch/home/actualite/infos/intemperies-d-aout-2005-un-evenement-record-avec-des-consequences/cosmo-leps-prevision-precoce-d-un-episode-de-precipitations-extremes.html.
[3] « Crues d’août 2005 – MétéoSuisse ». Consulté le 6 janvier 2021. https://www.meteosuisse.admin.ch/home/actualite/infos/intemperies-d-aout-2005-un-evenement-record-avec-des-consequences/cures-d-aout-2005.html.
[4] « Intempéries d’août 2005 – L’évaluation climatologique 10 ans après – MétéoSuisse ». Consulté le 6 janvier 2021. https://www.meteosuisse.admin.ch/home/actualite/infos/intemperies-d-aout-2005-un-evenement-record-avec-des-consequences/intemperies-d-aout-2005-l-evaluation-climatologique-10-ans-apres.html.
[5] rts.ch. « Intempéries de 2005: 44 millions distribués ». InfoSport, 18 septembre 2008. https://www.rts.ch/info/suisse/1153639-intemperies-de-2005-44-millions-distribues.html.
Featured Image of the article : Flooding of the camping in Altes Aaregg 2005. Image from chronicles of the National Platform for Natural Hazards
