These extreme water levels contain tides, analysis of wind-driven waves and existing measurements of natural and artificial coastal defenses. In this study, French researchers -from IRD, CNES, Mercator Océan- together with Dutch, Brazilian, Portuguese, Italian, and Nigerian colleagues, combined an unprecedented global digital model for surface elevation with new estimates of the extreme sea levels. Measuring past events to estimate future risks Although the magnitude and frequency of these events remain uncertain, scientists believe that countries in the tropics will be particularly affected.ĭespite the significant role ocean waves play in determining coastal sea levels, their contribution to coastal flooding had previously been largely overlooked, mainly due to a lack of accurate coastal topographic information. These episodic events are expected to become more severe and more frequent due to global warming, while the consequences will also increase due to increased anthropogenic pressure, such as coastal and infrastructure development, rapid urbanization. In addition to ongoing erosion and rising sea levels, these areas and their unique ecosystems are facing destructive hazards, including episodic flooding due to overtopping of natural/artificial protection, as in the case of Hurricane Katrina, which hit the United States in 2005, Cyclone Xynthia in Europe in 2010, and Typhoon Haiyan in Asia in 2013 (the largest tropical cyclone ever measured). Low-lying coastal regions host nearly 10% of the world’s population. This increase is principally caused by a combination of sea-level rise and ocean waves. Credit: © Rafaël Almar et al., Nature Communications.īy combining satellite data and digital models, the researchers have shown that coastal overtopping, and consequently the risk of flooding, is set to further accelerate over the 21st century, by up to 50-fold under a high emission global warming scenario, especially in the tropics. Schematic diagram of coastal overtopping.

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