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Flood warning

Thursday, 19 September 2019

Increasing hazard of flooding due to simultaneous storm surges and heavy precipitation in Northern Europe

The risk of flooding on Europe's coasts is steadily increasing, mainly due to the rising sea levels. If storm surges occur at the same time as heavy precipitation, the danger of flooding also increases. The storm surge blocks the rainwater from running of into the sea, causing coastal flooding especially in estuaries. Up until now, risk assessments have mostly assumed the effects of storm surges and heavy precipitation to be independent. These phenomena are, however, often triggered by the same weather pattern and, therefore, interrelated (so-called compound events). The hazard associated with their simultaneous occurrence is thus underestimated. An international team of researchers led by the University of Graz has investigated how climate change in Europe could alter the risk of flooding caused by heavy rainfall and storm surges. The results provide important information that should be considered in coastal adaptation planning in addition to the hazard imposed by sea level rise. The study was recently published in the journal Science Advances.

Scientists from the European Commission Joint Research Centre in Ispra, Italy, have used a mathematical wave and surge model to calculate how storm surges will be represented in climate model simulations in the future. The research group led by Douglas Maraun at the Wegener Center for Climate and Global Change at the University of Graz analysed these results jointly with precipitation simulations from climate models using a complex statistical model. ‘These results show that precipitation in Northern Europe is becoming more intense, so that the danger of simultaneous heavy precipitation and storm surges could steadily increase’, reports Douglas Maraun. In many river mouths, planners should prepare for increasing flood risk. In Southern Europe, another picture emerges: ‘In this region, the number of storm surges is likely to decrease, which should reduce the overall risk of simultaneous extreme precipitation’, says the climate researcher.

The results of these analyses can serve as a basis for additional, more detailed studies, which also take into account local conditions, such as the exact coastal topography and the presence of dikes, port facilities, or flood barriers.

Publication
Higher probability of compound flooding from precipitation and storm surge in Europe under anthropogenic climate change
E. Bevacqua, D. Maraun, M. I. Vousdoukas, E. Voukouvalas, M. Vrac, L. Mentaschi, M. Widmann
Science Advances, Vol. 5, no. 9, eaaw5531, 18 September 2019

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