Research press release


Nature Climate Change

Flooding risk rises for US coastal cities



今回、Thomas Wahlたちは、米国本土で高潮と豪雨が同時発生する確率を算定した。例えば、ニューヨーク市で観測された複合現象の増加の原因は、豪雨を起こしやすい高潮の気象パターンであり、高潮を伴う豪雨を主たる要因とする気象現象ではないことをWahlたちは明らかにした。また、高潮と豪雨の同時発生は、特定の条件下で、洪水リスクを105年に1回に上昇させた。これに対して、降水と高潮をそれぞれ独自なものと考えた場合の洪水リスクは、245年に1回だった。今回の研究では、米国沿岸地域で洪水が増えたことの主な要因は長期的な海水準上昇だが、人為的な気候変動と非人為的な気候変化と関連した高潮と降水の同時分布の変化によって洪水の発生可能性がさらに高まっていることが明らかになった。

The number of compound coastal flooding events driven by a combination of both storm surge and heavy precipitation has increased significantly over the past century for many major US coastal cities, finds a paper published online this week in Nature Climate Change. Such events are also shown to be more likely to occur on the Atlantic or Gulf coast than on the Pacific coast.

Nearly 40% of the US population resides in coastal counties and flooding in these usually low-lying, densely populated and highly developed regions can have wide-ranging social, economic and environmental consequences. When storm surge and heavy precipitation co-occur, the potential for flooding in low-lying coastal areas is often amplified compared with either phenomenon in isolation.

Thomas Wahl and colleagues determined the likelihood of the joint occurrence of these two phenomena for the contiguous United States. In the case of New York City, the authors determine that the observed increase in compound events is attributable to storm surge weather patterns that also favour high precipitation, as opposed to weather events primarily driven by high precipitation accompanied by storm surges. Under certain conditions, the combined event pushed the chances of flood risk to a once in 105 year event, compared with once in 245 years if precipitation and storm surges are thought of as independent. They find that long-term sea-level rise is the main driver for increased flooding along the US coastline, but changes in the joint distributions of storm surge and precipitation associated with climate change and variability further increase flood potential.

doi: 10.1038/nclimate2736

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