Sea level rise means a sharp increase in the flooding of coastal American cities, according to a report released late Tuesday by the Union of Concerned Scientists.

The analysis predicts that by 2030, Annapolis, Md. will see at least 180 floods every year, with some cities seeing two floods per day. By 2045, the trend will affect even more cities including Washington D.C. and Atlantic City, N.J., with half the cities studied expected to face more than 100 floods a year and nine towns expected to see flooding at least 240 times a year.

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While the researchers initially intended to focus on storm surges and hurricanes, they realized that flooding was the bigger story.

Climate Central's John Upton reports:

The researchers used intermediate-to-high sea level rise projections from the recent National Climate Assessment to guide their predictions for future coastal flooding rates. Those projections included a rise in sea levels of five inches between 2012 and 2030, and a rise of nearly a foot between 2012 and 2045. To help consider the effects of local conditions, such as the sinking lands of the mid-Atlantic coast, the group used data compiled by Climate Central’s team of scientists. The 52 locations, from Portland, ME, to Freeport, Texas, were selected because the National Weather Service issues flood advisories based on local tide gauge recordings there. That allowed the researchers to confidently use the tide gauge data to calculate historical flooding rates, and compare those with projected future rates. In the absence of flood-deflecting marshes, seawalls or levees, two-thirds of the 52 communities studied can expect a tripling in the frequency of high-tide flooding during the next 15 years, the researchers concluded. Half of the communities studied are expected to be flooded more than two dozen times every year by 2030.

"Around the world, sea level is rising in response to global warming. As the oceans heat up, the water expands and as glaciers and polar ice sheets melt they add water to the oceans," said Melanie Fitzpatrick, a UCS climate scientist. "Only international and national actions to deeply and swiftly reduce global warming pollution can slow the pace of future sea level rise."