Study in Alpine lakes traces 1,600-year of history climate change
By Summit Voice
SUMMIT COUNTY — While many recent research projects have highlighted the potential for more extreme weather as the planet warms up, a new study from the GFZ German Research Centre for Geosciences indicates that parts of the Alps saw more extreme flooding during periods of transition to cooler climatic conditions.
By studying sediment layers in the Mondsee, an Alpine lake near Salzburg, Austria, the researchers found evidence of flooding during the time of the Great Migration and the Early Middle Ages (AD 450-750), as well as the transition to the Little Ice Age (AD 1140-1520). In contrast, there was less flooding during the medieval warm phase (AD 1000-1140) and the coldest period of the Little Ice Age (AD 1600-1700).
The reason for more frequent floods during the cooling phase is probably a stronger inflow of moist Atlantic and Mediterranean air masses in the northern Alpine region due to a change in atmospheric circulation. The formation of a stable high-pressure cell over Siberia during colder periods, however, leads to a blockage of northbound low pressure cells and therefore less flooding in the Austrian Alpine foothills.
“We have used deposits from Lake Mondsee in Austria to create the first accurate calendar of floods and debris flow over the past 1,600 years in the Northeast Alps,” said GFZ scientist Tina Swierczynski. “Because of their annually laminated layers, the finely stratified lake sediments provide accurate information about flood events in times before instrumental records.”
Using microscopic analysis and modern geochemical element scanning, it was possible to identify traces of floods in the lake sediments to seasonal accuracy and to determine the frequencies of the floods.
“This study demonstrates that the frequency of floods in certain regions changes over long periods and no simple relation to climate change exists”, said lead researcher Achim Brauer.
To pinpoint regional variations, the researchers are doing similar studies in other lakes. Floods pose as a threat for human settlement and therefore require an accurate risk assessment. Above all, the question of the natural frequencies of such events is difficult to answer because the existing time series usually
lie no more than 100 years back.