The occurrence of devastating European floods correlates with large-scale fluctuations in atmospheric pressure known as the North Atlantic Oscillation (NAO). As scientists improve their predictions for the NAO, society will be better able to prepare for future flooding.
Stefano Zanardo and his colleagues at Risk Management Solutions in London, UK, analysed historical records of severe European floods going back to 1870, and compared them with the prevailing pattern of atmospheric pressure at the time of the floods. When the NAO is in its ‘positive’ state, a strong low-pressure system over Iceland funnels winds and storms across Northern Europe. Conversely, when the NAO is in its negative state, a weak low-pressure system over Iceland makes Southern Europe wetter than usual.
Floods in Northern Europe have tended to occur — and cause most damage — when the NAO was positive during winter, and when sufficient rain had already fallen for the ground to become saturated.
Atmospheric-pressure patterns over Europe may shift with future climate change, and officials should take this into account when assessing a region’s flood risk, the scientists say.