Current and future storm surge and stormwater flood risk under climate change in Chelsea, Massachusetts

Floods are some of the most devastating natural disasters and are expected to worsen under climate change due to intensification of extreme precipitation and sea level rise. In this study, present and future flood risk in Chelsea, MA is examined through changes in the 1% annual chance flood event. Future rainfall and storm surge are estimated for two time periods, 2041-2060 (2050) and 2071-2090 (2080) representing the mid and late 21st century, respectively, using a regional climate model and established sea level rise rates for the Boston area.

The output of these simulations show that the historical 1% annual chance rainfall event will be 3x and 3.5x as likely in 2050 and 2080, respectively. The historical 1% annual chance storm surge event will be 3.8x as likely in 2050 and occur at least once a year by 2080.

Using these estimates as inputs into a flood model reveals significant increases in flood risk across Chelsea. The percentage of land area in Chelsea inundated by the historical 1% annual storm surge event will increase from 14% in the present time period to 19% in 2050 and 34% in 2080. While storm surge events cause the greatest flood extents, the 1% annual chance rainfall event impacts the greatest number of buildings in the present time period and 2050. However, the 1% annual chance of joint rainfall and storm surge events impacts the greatest number of buildings in 2080. This finding underscores the need for including pluvial flood modeling in federal flood maps.

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