Last fall, as part of a massive report on climate change in New York, a research team led by Klaus Jacob of Columbia University drafted a case study that estimated the effects of a 100-year storm on the city's transportation infrastructure. Considering MTA Chairman Joseph Lhota’s comments today that Hurricane Sandy's impact on the subway was "worse than the worst case scenario," it seems pretty safe to put Sandy in the 100-year category. In that case, assuming the rest of the report holds true, the subway system could be looking at a recovery time of several weeks, with residual effects lasting for months and years.
The researchers modeled a potential 100-year storm that consisted of either a category 1 or 2 hurricane hitting nearby, or a severe nor’easter that coincided with high tide. (As we know now, Sandy was a hybrid of all three events.) The models predicted complete flooding of several tunnels after such an event, including all the tunnels in the East River: