【気候科学】沿岸部における洪水の発生頻度が倍増する恐れ

A predicted rise in sea level of five to ten centimetres by 2050 may double the frequency of coastal flooding events in many regions, particularly in the Tropics, according to a study in Scientific Reports. Based on their models, the authors suggest that a ten centimetre rise in sea level would double the potential risk for floods in high-latitude regions, notably the North American west coast (including Vancouver, Seattle, San Francisco and Los Angeles) and the European Atlantic coast.

Coastal flooding often occurs during extreme water-level events that result from simultaneous factors, such as large waves, storm surge and high tides. However, global estimates of increased coastal flooding due to a rise in sea level have not considered elevated water levels due to waves, and thus underestimate their potential impact.

Using extreme value theory - a statistical method for quantifying the probability or return of large events - Sean Vitousek and colleagues combined sea-level projections with wave, tide, and storm surge models to estimate increases in coastal flooding. The authors found that a five to ten centimetre rise in sea level, expected under most projections to occur between 2030 and 2050, would double the frequency of flooding events in many regions around the world. The authors suggest that cities such as Mumbai, Kochi, Grande Vitoria and Abidjan would be significantly affected by a five centimetre rise in seal level and a rise of less than ten centimetres doubles the risk of flooding over much of the Indian Ocean, the south Atlantic and the tropical Pacific.