As the frequency of major weather events increases, from Hurricane Katrina in 2005 to Hurricane Sandy in 2012—and now Hurricane Matthew—coastal cities are increasingly exposed to the risk of flooding. The concept of the 100-year storm—a storm that presents severe weather with a 1 percent likelihood of happening each year—is no longer an accurate measure of time when faced with rising coastal tides.
Exactly four years ago, we saw Hurricane Sandy devastate the eastern seaboard. The damages to New York alone cost $32 billion. And, as bad as it was, it could have been worse. For example, if Sandy’s storm surge had hit my hometown of Boston five hours earlier—and struck at high tide—almost 7 percent of the city would have flooded. While time was on our side during Sandy, that may not always be the case. Our sea levels are projected to rise 2.5 feet by 2050, which means a storm similar to Sandy will flood 30 percent of Boston. Today’s flooding risks are linked to extreme weather events, but have the potential to become a daily occurrence for coastal cities like Boston. If sea levels rise five feet by 2100—a likely possibility – Sandy-level flooding will become the new normal. This means twice a day at high tide 7 percent of Boston will flood. Under those conditions a moderate storm would submerge the entire city.