A report from catastrophe modeling firm AIR Worldwide, analyzes the damages resulting from the heavy rains that have caused widespread flooding and mudslides from July 11 to July 16 on the Southern Japanese Island of Kyushu.
AIR explained that a “very slow moving frontal system that developed over eastern China moved northeastward, bringing high levels of precipitation.” The resulting floods damaged “thousands of homes” on the island, mainly from “flash floods and landslides. Most of the residents who fled record flooding in southwest Japan are now returning to their homes. This event has been dubbed ‘Kyushu-Hikubu-Gou’ by the Japan Meteorological Agency (JMA), which translates to heavy rain event for northern Kyushu.”
Dr. Peter Sousounis, senior principal scientist at AIR Worldwide, explained: “Insurance policy conditions for flood can be more complicated than those for wind damage. Flood insurance does not exist as a standalone coverage in Japan. Instead, property owners can opt to purchase flood coverage as part of a standard fire insurance policy.
“This system evolved after typhoons in the early 1980s created a significant increase in the demand for insurance. In 1984, the Japanese insurance industry added coverage for typhoon wind (and flood) as part of the comprehensive homeowners’ insurance policy. Take-up rates for flood coverage, however, remain relatively low.”
“The chart below details typical residential property policy conditions. For commercial and industrial properties, the fixed percentage that is covered by insurance differs by account.
Loss ( percent of Sums Insured) Insurance Payout:
> 30 70 percent of Loss
15-30 Minimum of (10 percent Sums Insured, 2 M JPY)
< 15 Minimum of (5 percent Sums Insured, 1 M JPY)
Dr. Sousounis’ analysis continued: “The vulnerability of buildings to flood damage varies by construction type. For a given flood depth, a residential wood-frame building is expected to sustain more damage than a residential masonry building. Concrete construction is less vulnerable to flood than steel or masonry.
“Commercial and apartment buildings usually have stronger foundations than residential buildings, and are thus better able to resist flood loads. Flood vulnerability also varies by building height. Because damage is usually limited to the lower stories of a building, high-rise buildings will experience a lower damage ratio—the ratio of the repair cost and the total replacement value of the building—than low-rise buildings because a smaller proportion of the building is affected.”
“The flooding is also expected to take its toll on agriculture. Rice paddies have been particularly hard hit, with reports of widespread inundation. Take-up rates for rice insurance are high since it is a compulsory insurance in Japan. In 2009, the National Crop Insurance Services estimated that it was near 91 percent.”
As the storm moved further north the JMA issued a number of “heavy rain warnings,” which remain in effect for Fukuoka, Saga and Nagasaki prefectures. AIR pointed out that the “heavy rainfall has broken hourly and daily precipitation records in several places. The highest levels of rainfall were recorded in the city of Aso, situated at the base of the Mount Aso volcano; precipitation rates here reached as much as 108 millimeters (4 inches) per hour, accumulating to over half a meter (19.46 in) over a 24-hour period.
“As a result, as many as 500 landslides have been triggered by the event. The flooding and landslides have also been responsible for damage to as many as 100 roads and 20 bridges throughout the region. The event flooded the grounds of the famed Temple of the Golden Pavilion in Kyoto.”
According to AIR, the slow moving frontal system was part of an extra tropical low, a condition that typically affects southern Japan “during fall, winter, and spring but are not common so far south during the summer months. These lows typically have warm and cold fronts anchored to their centers that extend radially outward similar to the hands of a clock – usually oriented at the three and seven o’ clock positions, respectively.
“Heavy precipitation typically falls in the vicinity of these fronts. This particular low that formed during the period of July 9-16 had a wider separation of fronts (at the two and eight o’ clock positions) while the whole system moved slowly northeastward. The scenario resulted in the warm and cold fronts being slowly dragged in a parallel direction to Japan. Subsequently, individual rain cells began moving parallel to the fronts across Kyushu and a prolonged period of precipitation began that lasted for several days.
“The worst of the flooding has occurred in the Fukuoka prefecture, the northernmost prefecture of the island, where initial reports from the Fire and Disaster Management Agency suggest 6,895 residential buildings and 787 non-residential buildings have been affected. Elsewhere in Japan, the heavy rains have also caused some flooding in the Kyoto prefecture where 100 houses are reported to have flooded. Infrastructure and transport links have also been heavily impacted with widespread road closures and disruption to the rail transport network, particularly in the central region close to Mount Aso.
“The worst of the rainfall appears to have passed. Perhaps the greater threat would be the arrival of yet another system when soils are already fully saturated. Although typhoon Khanun is forecast to bypass the southern coast of Kyushu in a day or two, its precipitation shield could exacerbate the conditions.”
Source: AIR Worldwide
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