Flood Alp
Flood history of the Alps
Floods caused by extreme precipitation events represent one of the major natural hazards in the Alpine realm with several billions Swiss Francs of damage only in the last years. New climate models point to the possibility that flood frequency and intensities increase as a result of the upcoming climate changes. To scale these predicted changes of extremes, knowledge of the natural variety is required, which is, however, currently limited to only the historic period. This relatively short time interval may not represent the full range of values. No systematic record of Holocene Alpine flood activities exists to date.
This project aims to reconstruct the frequency and intensities of Holocene flood events in the Alps by using lake sediments as natural geologic archives acting as prehistoric recorders of extreme events. Lake basins record such extreme events with characteristic sediment layers, that contrast sharply the regular background sediments.
We propose to investigate twelve lakes in a north-south transect across the Alps, that cover also a range in altitude. The large numbers of lakes is required to provide a meaningful statistical base of flood events, so that regional patterns can be recognized and local outlayers can be avoided. The north-south transect provides information on the regional pattern reflecting synchronous or asynchronous behavior north and south of the Alps. Such differences would represent contrasting circulation patterns that control distribution of moisture and precipitation. Differing patterns between high and low-altitude lakes may provide information on seasonal flood distribution, because high-altitude lakes are frozen half of the year and can record flood events only during summer. The temporal pattern of flood reecords will be compared with independent curves of climate proxies, so that a potential climatic control (e.g. temperature, NAO-index) on flood activity can be evaluated.
The data will eventually yield crucial input to global and regional climate models for selected time windows. Several periods during the Holocene were characterized by warmer climate than today so that they may act as analogs to compare the reconstructed natural extremes with the modeled future scenarios characterized by increased temperatures and an accelarated hydrologic cycle.