Area of potential coastal and riverine flooding in Boston under various sea level rise scenarios (9-inch in 2030s, 21-inch in 2050s, and 36-inch in 2070s) at high tide and in the event of storms with an annual exceedance probability (AEP) of 10 and 1 percent.
Source:
Coastal flood hazard data created as part of Climate Ready Boston are a reanalysis of the coastal flood hazard data developed as part of the
MassDOT-FHWA analysis. In 2015, MassDOT released an analysis of coastal flood hazards using state-of-the-art numerical models capable of simulating thousands of potential nor’easters and tropical storms coincident with a range of tide levels, riverine flow rates in the Charles and Mystic Rivers, and sea level rise conditions.
Definitions:
9-inch Sea Level Rise: By the end of the 2050s, 9 inches of sea level rise is expected consistently across emissions scenarios and is likely to occur as early as the 2030s. 9” Climate scenario and coastal/riverine hazard flooding data are the MassDOT-FHWA high sea level rise scenario for 2030. Actual sea level rise value is 0.62 feet above 2013 tide levels, with an additional 0.74 inches to account for subsidence.
21-inch Sea Level Rise: In the second half of the century, 21 inches is expected across all emissions scenarios. 21” Data were interpolated from the MassDOT-FHWA 2030 and 2070/2100 data.
36-inch Sea Level Rise: The highest sea level rise considered, 36 inches, is highly probable toward the end of the century. This scenario has a greater than 50 percent chance of occurring within this time period for the moderate emissions reduction and business-as-usual scenarios and a nearly 50 percent chance for the major emissions reduction scenario. 36” Climate scenario and coastal/riverine hazard fooding data are the MassDOT-FHWA high sea level rise scenario for 2070/intermediate sea level rise scenario for 2100. Actual sea level rise value is 3.2 feet above 2013 tide levels, with an additional 2.5 inches to account for subsidence.
High Tide: Average monthly high tide is approximately two feet higher than the commonly used mean higher high water (MHHW, the average of the higher high water levels of each tidal day), and lower than king tides (the twice-a year high tides that occur when the gravitational pulls of the sun and the moon are aligned).
10% Annual Flood: A “10 percent annual chance flood” is a flood event that has a 1 in 10 chance of occurring in any given year. Another name for this flood, which is the primary coastal flood hazard delineated in FEMA FIRMs, is the “10-year flood.”
1% Annual Flood: A “1 percent annual chance flood” is a flood event that has a 1 in 100 chance of occurring in any given year. Another name for this flood, which is the primary coastal flood hazard delineated in FEMA FIRMs, is the “100-year flood.”
