AIRCurrents

Editor’s note: This September marks the 50th anniversary of Vera’s 50th Typhoon Vera, the most destructive typhoon ever to strike . A Anniversary: How a significant portion of the damage was the result of and in the years following Vera’s landfall, Japan responded by fortifying the Single Storm Prompted entire country against future storm surge events with a comprehensive a Nation to Reevaluate levee system. In this article, AIR principal scientist Dr. Peter Sousounis takes a look back at Typhoon Vera and performs numerical Disaster Prevention simulations of Vera’s storm surge to examine the effectiveness of Japan’s subsequent mitigation efforts. AIR would like to thank Mitsui Sumitomo Insurance Company and its consulting affiliate InterRisk Research Institute & Consulting, Inc. for their support and contribution 09.2009 to this article. by Dr. Peter Sousounis

A Most Destructive Typhoon On the eve of the landfall of Japan’s most destructive typhoon, newspaper headlines were unexceptional: “Typhoon will approach tomorrow night” and “Tokai in range of severe winds in the afternoon” are representative. The following evening, September 26th, 1959, a monstrous Category 4 storm with winds near 240 km/h came ashore west of Ise Bay in south-central Japan. The storm was dubbed Vera.1 Its record-high storm surge crashed over sea walls and breached coastal dykes that were hundreds of years old. Vera moved northeast over land toward Ise Bay, where its winds drove bay water toward Port. The port experienced storm surge of nearly four meters at 9:35 pm local time. Dykes caved immediately, giving people in Nagoya and surrounding villages little time to flee. The city of Nagoya was devastated in just three hours; its harbor— strewn with bodies, debris and timber from a local timber Figure 1. Six-hourly Track of Typhoon Vera with Central Pressure in Millibars (Source: AIR) factory—was subsequently described as a “sea of dead”. AIRCurrents 09.09|Typhoon Vera’s 50th Anniversary: How a Single Storm Prompted a Nation to Reevaluate Disaster Prevention By Dr. Peter Sousounis

Vera tracked quickly across , losing little strength of rivers and coasts. Workers built an 8-kilometer long over land. In the small village of Nagano in central Japan, dyke around Nagoya Port and surge defense systems were high winds ripped the roofs from hundreds of traditionally constructed on other major bays in Japan, including those constructed wooden homes. Heavy precipitation swelled in Tokyo and Osaka. These systems were designed to handle rivers so greatly that they spilled over their banks. Landslides water levels based on the storm surge produced by Typhoon were widespread. Conditions remained treacherous even Vera. Measures were also put in place to reduce the rate after Vera’s departure. Muddy water continued to pour of land sinking around Ise Bay from underground pumping through breaches in dykes on the south-central coast for activity—which had been about 10 centimeters per year by several days until they were finally repaired. Because the the time Vera struck. area just north of Ise Bay is at or even below sea level, some districts remained flooded even 100 days after the storm. The Disasters Countermeasures Act required annual reports on prevention-related activities and promoted public Altogether, Typhoon Vera flooded more than 360,000 awareness through the annual observance of Disaster homes, of which 190,000 were submerged2 (Oda, 2006). Prevention Day. At the local level, government officials Another 830,000 homes sustained some level of damage. and citizens began participating in Disaster Management The storm killed an estimated 5,000 people and injured Councils and drafted disaster management plans specific to 66,000. Much of the damage was in Aichi and Mie their regions. prefectures. Vera’s destruction marked a turning point in Japan’s approach to coping with catastrophes. Previously, Japan Impact on Japan’s Disaster Awareness had been response-oriented. In Vera’s aftermath, the and Insurance Industry focus was on prevention. Officials invested in upgrades Japan is prone to natural disasters and the decade that for disaster information communication systems, as well followed World War II saw numerous large-scale events, as improvement of weather observations and forecasting including the Nankai earthquake in 1946, the Fukui technologies. earthquake two years later, Typhoon Tess in 1953 and Vera in 1959. These events left thousands dead, yet it Vera has ultimately had a tangible impact on the insurance was not until Vera that the situation was addressed by the industry. It has become the event used by insurers and government. Typhoon Vera was the catalyst for developing reinsurers to define the reserve for a 70-year return period and strengthening the disaster management system in event. An amendment to the enforcement regulations Japan. of the Insurance Business Law on April 1, 20053, requires insurers to base their catastrophe reserves for windstorm On September 27th, even as Vera was still unfolding, or on recurrence of Typhoon Vera. This increases local governments set up disaster relief headquarters the minimum windstorm return period for reserving and and invoked the Disaster Relief Act. Refuge shelters were reinsurance purposes from 20 years to 70 years. opened and victims were rescued using helicopters and boats. On September 29th, the national government Numerical Simulation of Vera’s Storm got involved, creating the Central Japan Disaster Relief Surge Headquarters. Defense forces joined in evacuation efforts, The storm surge from Vera had a significant impact on the and truckloads of food and shelter items poured in from Ise Bay region because of shallow bathymetry, the intensity around the country. of the storm, the low elevation of the land surrounding the bay, and the lack of a resilient defense system. Immediately after the storm, the government launched a full-force rebuilding initiative. Within a few months, the Law To investigate the adequacy of Japan’s current defense for Special Measures to Promote Storm Surge Protection system and how it would respond to a recurrence of was passed to implement measures for the protection Typhoon Vera, AIR used a modified version of the Princeton of land and people from storm surge; other legislation Ocean Model (POM). The POM is a numerical grid point addressed threats from inland flooding. Permanent model capable of modeling not only ocean currents and restoration works began as part of a five-year plan, and two million people were put to work on the embankments

2 AIRCurrents 09.09|Typhoon Vera’s 50th Anniversary: How a Single Storm Prompted a Nation to Reevaluate Disaster Prevention By Dr. Peter Sousounis waves in deep water, but also storm surges along coastlines. It has been used in many instances to evaluate storm surge in Japan (Minato 1998; Hong and Yoon 2003; Kohno and Higaki 2006). Although the basic model has been available for more than two decades, a relatively new feature is POM’s ability to explicitly model the inland penetration and hence, the depth of the surge (Oey 2005).

To create the wind field for modeling the surge, AIR performed a simulation of Vera over water using the AIR Typhoon Model for Japan. Best Track Data from the Japanese Meteorological Agency was used to generate Figure 2. AIR model simulation of RecurVera storm surge. a) Water elevation above mean sea level (shading indicates cm above mean sea level) and surface wind wind speeds and wind directions every 15 minutes, and velocities (arrows are in m/s) at 22:15 LST. b) Maximum inland flood depths (cm). this information was fed into POM. A normal astronomical (Source: AIR) tidal cycle was added and timed to optimally phase with the A second scenario was modeled to explore what would maximum storm surge at Nagoya Port. happen were a storm stronger than Vera to occur. From a meteorological (or central pressure) perspective, a storm as Two scenarios were modeled. The first was a recurrence intense as Vera striking somewhere between Kagoshima of Vera (RecurVera), which is shown in Figure 2. This and Tokyo has a return period of about 50 years. AIR’s simulation modeled the meteorological aspects of Vera simulation took Vera’s central pressure and subtracted from exactly as they occurred throughout the storm’s lifetime it 10 hectopascals, or milibars. This IntenseVera storm has and the present-day levee system around Ise Bay—but an estimated return period of about 200 years. Once again, assumed widespread collapse at some point during the the IntenseVera simulation used the present-day levee event. Figure 2a shows surge heights across Ise Bay at the system around Ise Bay, but this time assumed a more limited time of maximum surge, before the levees collapsed. It is levee breach at some point during the event. The breach noteworthy that while the levees remained intact, they was imposed in the vicinity where the surge height and were sufficient to prevent water from overtopping and water velocity were greatest for this event. The astronomical causing flooding. Impressively, the simulated magnitude and tidal cycle was again phased to cause the highest surge timing of the high-water mark at Nagoya Port was within height possible. 20 centimeters (higher) and 45 minutes of the observed values. This slightly higher high-water mark is likely the The surge heights across Ise Bay for IntenseVera shown result of using the normal astronomical tidal cycle rather in Figure 3a reveal that even though the maximum surge than the slightly damped one that occurred during Vera’s height is 0.4 m higher than in the case of RecurVera, an actual landfall. intact levee system is still adequate to keep flooding to a minimum. After the partial levee breach, however, there The flood footprint in Figure 2b represents the situation is a markedly different result. The flooding that results is after the levees collapsed. The simulated inland penetration not quite as extensive as that from RecurVera because the of 20 km compares well to Vera’s observed flood footprint. levee, although damaged, still provides some defense. From Additionally, the greatest inland penetration in the model a loss perspective, however, it should be remembered that occurs in the region that is slightly below sea-level, which that there is more exposure in the region than there was in was also observed during Vera. 1959. Importantly, note that the farthest inland penetration of flood water is just west of Nagoya City.

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And Along Came Bart Despite Japan’s admirable focus on disaster awareness, prevention, and management, Super Typhoon Bart in 1999—forty years later almost to the day as Vera and ten years ago this month—proved that catastrophes will continue to occur. Winds from Bart damaged approximately 100,000 homes and precipitation and surge flooded 20,000 more (Non-Life Insurance Rating Organization of Japan, 1999). By AIR’s estimation, damage from a recurrence of Super Typhoon Bart would reach JPY 496 billion (USD 5 Figure 3. AIR model simulation of IntenseVera storm surge. a) Water elevation above mean sea level (shading indicates cm above mean sea level) and surface billion). Again, as with Vera, Bart’s damage was caused by wind velocities (arrows are in m/s) at 22:15 local standard time (LST). b) the worst possible combination of conditions. The storm Maximum inland flood depths (cm). S( ource: AIR) arrived at high and made landfall at the farthest end of a bay open to the southwest. Conclusion Storms of Vera’s size and intensity will undoubtedly occur Bart brought record-high surge levels that exceeded old again. However, as a result of the last such experience, records by more than two meters and collapsed numerous Japan took important steps to mitigate their effects. levees. After Bart, insurance companies paid out the third largest claims bill ever recorded in the Japanese non-life The numerical surge modeling presented in this article insurance market, after in 1991 and represents research currently underway at AIR—research in 2004. that will be used to enhance future releases for the AIR Typhoon Model for Japan to more accurately estimate not only the meteorological aspects of the typhoon peril, but also the mitigating effects of the technological structures in place today.

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References AXCO, 2009, Insurance Market Report, Japan: Non-Life (P&C), AXCO Insurance Information Services, London, UK.

Hong, C.-H., and J.-H. Yoon, 2003: A three-dimensional numerical simulation of Typhoon Holly in the northwestern Pacific Ocean, J. Geophys. Res., 108(C8), 3282, doi:10.1029/2002JC001563.

Kohno, N., and M. Higaki, 2006: The Development of a Storm Surge Model Including the Effect of Wave set-up for Operational Forecasting. Papers in Meteorology and Geophysics, Vol. 57.

Minato S., 1998: Storm surge simulation using POM and a revisitation of dynamics of sea-surface elevation short-term variation. Meteorology and Geophysics, 48, 79-88.

Non-Life Insurance Rating Organization of Japan, 1999: Report of Disaster Survey for Typhoon 9918. 54.

Oda, H., 2006: Typhoon Isewan (Vera) and its Lessons. Japan Water Forum Report, Tokyo Japan. 60 pp.

Oey, L-Y, 2005: A wetting and drying scheme for POM. Ocean Modelling, 9, 33–150.

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1 The Japan Meteorological Agency, which assigns numbers rather than names to , made an exception in this case after the fact, calling it the Isewan Typhoon because of its destruction of the Ise Bay (wan) region.

2 Submersion indicates flooding to the first floor level.

3 Privatization of the Japanese insurance market didn’t happen until 1996, and regulating catastrophe reserves was not a priority until nine years later, in 2005, the year after ten typhoons—more than twice the annual average—made landfall in Japan.

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