Coastal protection flooding accelerated due to weather phenomena

The combination of sea level rise, tides, storm surge and waves has accelerated the flow of natural and man-made coastal protection by about 50% in the past two decades.

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This revelation comes from an international study coordinated by the IRD, in which international partners are participating. The study was published in Nature Communications.

By combining satellite data with digital models, researchers have shown that coastal flooding, and thus flood risk, will accelerate further during the 21st century, up to 50 times in a high-emissions global warming scenario, especially in the United States. Tropical region. This increase is mainly due to rising sea levels and ocean waves.

Low-lying coastal areas are home to nearly 10% of the world’s population. In addition to continuous erosion and sea level rise, these areas and their unique ecosystems face devastating risks, including occasional flooding due to the overflow of natural/man-made protections, as in the case of Hurricane Katrina, which hit the United States in 2005, and Hurricane Xynthia in Europe. in 2010, and Typhoon Haiyan in Asia in 2013 (the largest tropical cyclone ever measured).

These episodic events are expected to become more severe and frequent due to global warming, while the consequences will also increase due to increased human pressure, such as coastal and infrastructure development, and rapid urbanization. Although the magnitude and frequency of these events remains uncertain, scientists believe that countries in the tropics will be particularly affected.

Despite the important role of ocean waves in determining coastal sea level, their contribution to coastal flooding was previously largely overlooked, mainly due to the lack of accurate coastal topographic information.

In this study, French researchers from the IRD, CNES and Mercator Océan, along with colleagues from the Dutch, Brazilians, Portuguese, Italians and Nigerians, combined an unprecedented global numerical model of surface height with new estimates of extreme sea levels. These extreme water levels contain analysis of wind-driven tides and current measurements of natural and man-made coastal defenses.

The study began by measuring the increase in global inundation events that occurred between 1993 and 2015. To achieve this, satellite data were used to define two key parameters of coastal terrain: the local beach slope and the maximum subaerial height of the coasts. . The maximum coastal water level was calculated at time intervals to determine the likely annual number of hours during which coastal defenses could be bypassed in each area.

“The combination of tides and large wave outbursts is the main contributor to coastal spill events,” says Rafael Almar, IRD researcher in coastal dynamics and study coordinator. “We identify hot spots, where the increase in overtaking risk is greatest, such as in the Gulf of Mexico, the southern Mediterranean, West Africa, Madagascar and the Baltic Sea.”

The scientists also conducted a preliminary global assessment of potential coastal flooding during the 21st century, taking into account different scenarios of sea level rise. The results show that the number of overrun hours can increase at a faster rate than the average rate of sea level rise.

“The frequency of excesses is significantly accelerating and will be clearly noticeable from 2050, regardless of the climate scenario. By the end of the century, the intensity of the acceleration will depend on future trajectories of greenhouse gas emissions, and therefore on sea level rise. If a scenario exists, the intensity of the acceleration will depend on future trajectories of greenhouse gases For high emissions, the number of hours exceeded worldwide could double by fifty compared to current levels.

“As we move into the 21st century, more and more areas will experience flooding and consequent coastal flooding, especially in the tropics, the northwestern United States, Scandinavia and the Russian Far East.”

Further studies at local and regional levels will be required to achieve these global projections, which provide a solid basis for suggesting effective adaptation measures in identified hotspots.

With information from Europa Press

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