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Environment Climate Change Cyclones Flooding

Tropical Cyclones: Asia in the Eye of the Storm

An interview with Director of Guy Carpenter Asia Pacific Climate Impact Centre at the School of Energy and Environment, City University of Hong Kong

As parts of coastal China, Hong Kong, and Macau respond to the destruction of Typhoon Hato, which hit the region Wednesday and resulted in deaths, blackouts, severe flooding, and closures of schools, businesses, train stations, and airports, a 2017 report predicts the overall number of tropical cyclone landfalls in East Asian countries is expected to be below normal.

The report from the Guy Carpenter Asia-Pacific Climate Impact Centre at the School of Energy and Environment at City University of Hong Kong outlines predictions for tropical cyclone formations and landfalls.

Certainly, the occurrence of any such event is significant. Typhoon Hato is estimated to have already resulted in an economic loss of about HK$8 billion ($1 billion), based on the average daily value of the economy’s gross domestic product in 2016.

BRINK Asia spoke about the impact of cyclones on natural ecosystems with Professor Johnny Chan, chair professor of Atmospheric Science and dean of the School of Energy and Environment at City University of Hong Kong. Dr. Chan is director of the Guy Carpenter Asia-Pacific Climate Impact Centre at the School of Energy and Environment.

BRINK Asia: What are the 2017 predictions for tropical cyclone formations and landfalls on East/Southeast Asia? Who is most affected?

Dr. Chan: We actually make two predictions. One is the prediction for the entire western north Pacific Ocean, which includes countries like Vietnam and goes all the way to the east until the dateline, and from the equator all the way up north to Japan. We usually look at the period from 1 May to 31 October. This year, according to our model predictions in May, the number of cyclone formations will be 24, while the average is 26 from May to October.

Then we also look at the different coastal regions as people are more concerned about how many of these cyclone formations will make landfall in their region; and in doing so, we split the coastal regions into three parts: Japan and Korea; Eastern China and Taiwan; and Southern China, Vietnam, and the Philippines.

This is because these are the three main trajectories of tropical cyclones—one hitting each of these regions. That is why we separate them into these three areas.

Table: Historical and predicted averages of tropical cyclone landfalls from May to October

Our model predictions show that all three areas were forecast to have fewer numbers of tropical cyclones between May and October this year. In Japan and Korea, on average, we see about five, and we predict to have three. In Eastern China and Taiwan, the average is about four, and we expect to see three; and for Southern China, the Philippines and Vietnam, it is roughly about the same at seven.

BRINK Asia: What impact does global warming have on the intensity or frequency of cyclones?

Dr. Chan: There is still no complete consensus as to whether the number of tropical cyclones will increase, decrease, or stay the same as a result of continued global warming. This is because although global warming will definitely warm the ocean and hence provide energy to the atmosphere for tropical cyclones to form, it is not clear whether other factors governing tropical cyclone formation may also be favorable.

There is clearly a consensus, however, that even if the number of tropical cyclones is to stay the same or roughly the same in the coming years, global warming is going to produce more heavy rain, simply because with global warming you have more evaporation getting into the atmosphere; so there is more moisture in the atmosphere. With more moisture in the atmosphere, the rains will be heavier.

So even if we assume that the intensity and number of cyclones stays the same, there will still be heavier rain, which means that the potential for severe flooding and landslides will be higher in the event of tropical cyclones. In that regard, global warming is related to the bigger impact of tropical cyclones even though [their] frequency of occurrence may not change.

BRINK Asia: What are some of the key risks related to tropical cyclones?

Dr. Chan: For East Asia, the main impact of tropical cyclones is the flooding in coastal regions. Flooding happens mainly due to two factors—one is the heavy rain associated with tropical cyclones; the second is the “storm surge,” which is water coming in from the ocean. The “storm surge” also happens due to two effects—the first is that of the strong winds pushing the water onto the land; the second is an occurrence of lower pressure at the top of the cyclone, which increases water levels. If you add this, then you will almost certainly see flooding. These are the major effects of tropical cyclones from a flooding perspective.

A related effect of the heavy rainfall associated with tropical cyclones is landslides. Many regions in Asia, even along the coast, could be very mountainous. If you have heavy rain in a mountainous area (where trees have been cut either for logging purposes or even for household consumption), then the top soil along the slopes is no longer held together and can be easily washed away by heavy rain. As a result, the whole slope could fall, causing severe landslides that can result in big losses of property and life.

Another impact that is talked about is that of high wind speeds when cyclones hit, but in many of the coastal areas across East Asia, with the exception of a few shanty towns, houses are made of bricks so they cannot be blown away easily. As a result, the damage from wind speeds pales when compared to flooding. As far as insurance is concerned, the major damage caused by winds is the downing of power lines across affected areas.

A second part of this interview to be published will discuss the economic and other tangential implications of tropical cyclones and what governments and insurance companies can do to mitigate the risks resulting from them.