Hong Kong Baptist UniversitySlow-moving tropical cyclones bring greater flood risks

Slow-moving tropical cyclones bring greater flood risks

A new study at Hong Kong Baptist University (HKBU) has revealed that slower tropical cyclone movement tends to elevate rainfall volume, leading to greater flood risks at a regional scale. The research findings were published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Led by Dr Li Jianfeng of the Department of Geography, the research team investigated 406 tropical cyclones which made landfall and lasted for more than two days over the coast of China, and specifically the Pearl River Delta, between 1961 and 2017. Using datasets and tools for studying tropical cyclones and climate behaviour, the team found that the observed average moving speed, or translation speed, of the tropical cyclones underwent a significant drop of 11%, decreasing from 21 km per hour in 1961 to 18.6 km per hour in 2017.

Following statistical analysis, the HKBU team detected a negative correlation between tropical cyclones’ moving speeds and local rainfall volume, with evidence showing that slow-moving tropical cyclones brought about 20% more rainfall on average when compared with fast-moving ones.

“The total amount of rainfall over a specific region brought about by a tropical cyclone is directly proportional to rainfall intensity, and inversely proportional to moving speed. The slower a tropical cyclone moves, the longer it spends passing over the region. As the region is affected for a longer duration, slower tropical cyclones bring about more rainfall,” said Dr Li.

Dr Li Jianfeng, Assistant Professor of the Department of Geography

The study also found that the occurrence of slow-moving tropical cyclones became more frequent after 1990, indicating an increase in flood risks in the Pearl River Delta region in recent years.

The discovery offers invaluable insights that will enable the development of better flood management and adaptation strategies in the coastal region of China which is under threat due to tropical cyclones. 

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Faculty of Social Sciences
Department of Geography

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