Rethinking Of Typhoon’s Randomness And The Impact On Economy

By Dr. Hiroshi Takagi 20 October, 2020

See why Dr Takagi from Tokyo Tech thinks typhoons have an unpredictable random nature & what we should do about it

My research field is on the risk of coastal hazards, with a focus on Asia. A strong research interest among many is to analyse the statistical variability of typhoons and the associated risks of storm surges and high waves.

Cyclone Nargis caused a huge storm surge that killed ~140,000 people in Myanmar; not a high risk country

I first became interested in this issue when I studied Cyclone Nargis, which made landfall in Myanmar in May 2008. This cyclone caused a huge storm surge that killed an estimated 140,000 people. It is well known that neighbouring Bangladesh is the most at risk of tropical cyclones in the world.

By contrast, prior to Nargis, Myanmar was not considered to be a high typhoon risk country. Although the typhoon itself had made landfall even before then, Nargis’ path turned out to be a very unusual route. It made landfall on the southern coast and hit its largest city, Yangon. None of the residents, including the elderly, had ever experienced a strong typhoon before.

The nature of typhoons is fundamentally of a rather unpredictable random nature

Since that study, I have come to believe that the nature of typhoons is fundamentally of a rather unpredictable random nature that does not fit clearly into any probability distribution. Many recent media reports have tried to link the frequent occurrence of strong typhoons to the problem of climate change at all costs. For example, the Japan Times quoted the comment of one of Ministries after Typhoon Faxai, which severely hit Tokyo Bay in 2019, said “Due to climate change, various changes, including wind speeds and rainfall that go beyond common expectations, are occurring”.

It is true that Typhoon Faxai was one of the strongest typhoons ever. The table below shows the rank of the high waves observed at Tokyo Port, demonstrating that the wave recorded during Faxai was the highest at least over the last five decades. However, it should be noted that there were other typhoons of the same level in the past. The other equivalent high waves over 3 m high were also caused by the past typhoon events, Irma in 1985 and Danas in 2001.

Climate change under global warming may intensify future typhoons. However, I don’t believe that long-term climatic variability alone can adequately explain the fickle randomness of typhoons.

“I don’t believe that long-term climatic variability alone can adequately explain the fickle randomness of typhoons”

It is more important to consider factors such as the frequency of typhoons that hit a narrow bay with a concentration of economic assets on the worst possible course. Furthermore, from a disaster management perspective, I think it is more important to consider how much the risk of strong typhoons has potentially increased in areas, where have not experienced strong typhoons over the past few decades, due to population growth, economic development, urban development, etc.

We recently published a paper on this point. The target country is Vietnam, a typhoon-prone country with a long north-south coastline. Most of the major cities (e.g. Hanoi, Ho Chi Minh City, Da Nang, and Hoi An) are located close to the sea, so it would be possible to reveal a clear relationship between typhoons and damage because the typhoon’s energy doesn’t diminish much as it hits these cities.

As for human damage, the number of victims has been decreasing in recent decades due to improvements in Vietnam’s typhoon disaster prevention, but economic damage has been increasing over time. In 2017, the damage caused by the disaster reached a record high of USD1.5bn, mostly caused by typhoons.

We analysed this factor using statistical methods such as principal component analysis, which is a mathematical method for revealing characteristic statistical trends among many factors. The results show that there has been no significant trend in meteorological factors such as the frequency and strength (wind speed and central pressure) of typhoon landfalls for at least the past 40 years. On the other hand, there was a strong correlation between the overall strength of typhoons and economic damage (below figure).

Although the frequency of typhoons did not increase nationally in the decade 2008-2017 compared with the previous decades, the frequency of landfall was significantly higher in the northern region of Vietnam between 20 and 22 degrees north latitude, with Hanoi and Haiphong (below figure). In other words, the recent increase in economic damage may be mainly due to the fact that strong typhoons frequently happened to hit place by chance where the economy is concentrated.

By contrast, areas that have not experienced major typhoons in the past few decades may have experienced steady economic development during this calm period.

The risk of typhoons in ‘calm’ areas (usually with economic value) need to be re-evaluated

However, the potential risk of typhoons might be very high in such areas due to the growing economic value, the low level of preparedness and people’s lack of awareness of the disaster risks. The risk of typhoons in such areas needs to be re-evaluated.

Waves of 3 m are not uncommon in the open ocean, but they are quite rare in the inner bay, such as Tokyo Bay, occurring only once every 10 to 20 years. Most of these unusual high waves are caused by typhoons, as shown in the above table.

Conversely, unless the typhoon hits, the waves are usually very calm in the inner bay. If the period of calmness is sustained, the port developments and industrial activities are promoted, resulting in the regional population growth. However, at the same time, people’s awareness of disaster risk is reduced, and the next direct hit typhoon may cause unexpected damage to the coast with low defense design levels (below photo).

Therefore, it is necessary to consider that the period when the climate is mild is the period when the risk of future disasters increases, and disaster prevention measures should be taken.

More On Sea Level Rise

• It’s Time To Prioritise Sea Level Rise – CWR’s Debra Tan says it’s time to be FOMO about our rising seas. From emission accelerants to accelerated impacts she runs through three reasons to rethink our attitudes towards sea level rise – it’s a big deal, sea level rise is worse than you think. This time, even she’s depressed
• Sea Level Rise – What The Science Tells Us – What’s the latest on sea level rise projections? HKU’s Dr. Nicole Khan shares key findings from her survey of 100+ sea level experts, as well as talks risks to Hong Kong and what we should take away from COVID-19
• The Present & Future Flood Risks In Bangkok – The nature of flood risks in Bangkok are complex and there is yet to be any holistic plan or authoritative projections on SLR for Bangkok. Chulalongkorn University’s Dr. Chanita Duangyiwa breaks it down & looks ahead
• Awareness Of Typhoon Risks In Mekong – Vietnam is already vulnerable to typhoons and climate change will increase the number and intensity of typhoons. Yet, awareness and preparedness among locals are inadequate. Dr. Le Tuan Anh & Dr. Hiroshi Tagaki unpack why
• Typhoons And Storm Tides Risks In Guangdong – Already vulnerable Guangdong Province, accounts for 34.5% of typhoons landing on China, has to now also deal with increasingly unpredictable storm tides and escalating damage. SYSU’s Dr. Xiaohong Chen & Huiwen Bai expand

Further Reading

• Return Periods – Are They Still Useful For Floods? – Flood return periods aren’t ‘returning’ on time and actually are getting worse so are they still useful? CWR’s Yuanchao Xu says they are. See why he thinks this & how they are calculated
• Thirsty And Underwater: Rising Risks In Greater Bay Area – How will water & climate risks, including rising sea levels & droughts, threaten the already water-stressed Greater Bay Area (GBA)? CWR’s Tan & Mirando explain in their latest CLSA report and highlight companies’ failure in climate risk disclosures
• No-Sense Climate Strategies: From DSD To HSBC – Hong Kong’s shortsighted & unrealistic climate plans will leave key assets & infrastructure exposed that mean the government, companies, investors and the public are even more exposed. China Water Risk’s Dharisha Mirando & Debra Tan expand
• Capital Threats Remain Post COVID – There is no vaccine for climate & water risks, yet some in the financial sector are still burying their heads. CWR’s Dharisho Mirando reminds us how our capital is at risk & steps we can take to reduce them while going green
• Building Flood Resilience For Hong Kong – HK is the rainiest city in the Pacific Rim and with the threat of climate change, it’s heading for a wetter future. The Drainage Services Department’s senior engineer Patrick Chan shares the city’s strategies to improve flood resilience