China Braces for Another Typhoon; Japan on Alert: AIR Analysis

August 8, 2012

According to catastrophe modeling firm AIR Worldwide, residents along coastal cities in eastern China are preparing for their third typhoon in less than a week. Just last weekend, two powerful typhoons—Damrey and Saola—came ashore less than 10 hours apart, causing widespread, if moderate, wind damage.

Meanwhile, Typhoon Haikui, the 11th tropical storm of the Pacific season, has been upgraded to a severe typhoon. The Japan Meteorological Advisory’s bulletin at 15:45 UTC on August 7, said the typhoon is located approximately 420 kilometers [app. 293 miles] south-southeast of Shanghai, China, moving 10 km/h [6.25 mph] in a northwest direction.

AIR described Haikui as “a large storm with radius of storm-force winds around 180 km/h [112.5 mph]. Maximum 1-min sustained wind speeds are 140 km/h [87.5 mph] (with gusts up to 175 km/h [app. 110 mph]), making it a Category 1 hurricane on the Saffir-Simpson scale.

The typhoon prompted the China Meteorological Administration to raise the storm warning system to red alert status—its highest level—indicating hurricane-force winds of 118 km/h (73 mph) or more.

“The storm is expected to maintain its present northwest movement as it churns toward the eastern coast of China,” explained Dr. Peter Sousounis, senior principal atmospheric scientist at AIR Worldwide. “Typhoon Haikui is forecast to weaken slightly before making landfall as a weak Category 1 storm just north of Wenzhou, Zhejiang province at 8 pm EDT this evening (0000 UTC).

“Because of the storm’s large size, the duration of damaging winds will likely be more than 24 hours in many coastal locations. Haikui is then expected to weaken further as it moves inland, reaching Hangzhou within 12 hours of landfall and possibly Shanghai within the next 24 hours.

“Typhoon Haikui is tracking a path similar to another storm that wreaked havoc a few years ago in nearly the same region. In August 2004, Typhoon Rananim made landfall just south of where Haikui is expected, and brought high winds and heavy rain to Wenzhou,” he continued.

“Maximum one-minute sustained winds as high as 160 km/h [100 mph] were observed 50 km 31.23 miles] to the right of Rananim’s center, and higher gusts were likely. Rananim had a narrow precipitation shield, but heavy precipitation rates near landfall caused nearly 400 mm [15 ¾ inches] to fall in Linhai, located in the central Zhejiang province.

“Rananim was the strongest typhoon in the area since Winnie (1997), and damaged or destroyed over 130,000 homes and left 270,000 hectares of farmland in ruins. If Rananim were to recur today, AIR estimates insurable losses would be approximately RMB 6 billion [$943 million], while insured losses would be around RMB 1 billion [$157 million].”

AIR noted that “due to the slow-moving nature of Haikui, the China Meteorological Administration is expecting that the outer bands of the systems will bring torrential rain across the island and strong winds to coastal cities. China’s mountainous coast may enhance precipitation on the north and east sides of Haikui on its approach to China, creating significant flood and landslide hazards. In Zhejiang, waves up to 5.9 meters [app 20 feet] high have been reported along the coast of Xiangshan, a coastal area of Ningbo, forcing thousands of vessels to seek refuge.”

Dr. Sousounis pointed out: “Since the late 1940s, China has continued to strengthen flood control measures. To that end, more than 280,000 km [175,000 miles] of embankments, 86,000 reservoirs, and 97 key flood retention areas have been completed to protect the country against future flood losses. Thus, flood risk in China depends on both the accumulated runoff (which is a function of precipitation level, topography, and soil conditions) and flood defenses, which vary by region.”

According to AIR, “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 (which may experience surface corrosion and rust-induced expansion) or masonry structures (whose weak connections between building elements makes it permeable to water). Concrete buildings have a strong frame structure, but may suffer from cracking and rebar expansion. Commercial buildings usually have stronger foundations than residential buildings, and are thus better able to resist flood loads.

“Adobe and brick with wood-frame have been the predominant construction types for single family homes in China, and they are still widespread in rural areas. These are usually poorly engineered structures and generally not insured. Insured single-family homes are predominately confined masonry and reinforced concrete. Concrete is less vulnerable to flood loads, and also to lateral wind loads.”

Source: AIR Worldwide

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