One million evacuated as typhoon Chan-hom makes land fall could end up producing catastrophic flooding in low-lying Shanghai
China's Xinhua state news agency reports the country was on its "highest alert" as Typhoon Chan-hom approached Shanghai, its largest city, on Friday.
Coastal flooding is the biggest risk: Think New York City during Hurricane Sandy.
If you're in Shanghai, now's a good time to head for higher ground.
In advance of a rare landfall near the city of 23 million people expected on Saturday morning local time, China has begun to hunker down.
Xinhua reports one million people have been evacuated in Zhejiang province, just south of Shanghai, where Chan-hom's landfall and worst conditions are expected.
Trains, flights, and shipping routes have all been suspended in one of the world's most active economic zones.
The latest weather models are also showing a last-minute bend to the right in Chan-hom's expected track, as well as a broadening of the storm's area of strongest winds, which further complicates the outlook for Shanghai.
Still, Chan-hom remains an unusually large typhoon-with cloud cover roughly the size of Alaska.
The larger a storm like this is, the more water it can push ashore, boosting the risk of a dangerous storm surge.
The latest coastal inundation models show Chan-hom's storm surge could exceed 20 feet around Shanghai, dangerously close to the 22.6-foot height of the city's downtown seawall barrier, which is supposed to be able to protect against a 1-in-1,000-year flood.
Depending on the exact track the storm's center takes, Chan-hom could end up producing catastrophic flooding in low-lying Shanghai-or not.
Shanghai sits in a vulnerable location at the mouth of the Yangtze River, and typically ranks high on lists of cities most at risk of sea level rise.
Over the next 50 years, if current projections hold, nearly a quarter of its residents and $1.7 trillion in assets will be underwater.
In addition to rising seas, Shanghai's land is also sinking under the weight of new urban infrastructure and excessive groundwater pumping-accelerating the sea's yearly advance.
Other meteorologists I consulted said Chan-hom's latest expected track-while keeping the worst winds just offshore-may actually worsen coastal flooding by piling up extra water in the Yangtze.