Flood and storm surge are significant risks in Maine. In the event of extensive inland or coastal flooding, evacuation may be required. For individuals and households with limited mobility, either due to inadequate access to transportation options or because of physical limitations, evacuation presents heightened risk. Evacuation may also prove especially difficult for individuals and households due to limited economic resources, difficulty understanding or accessing information, or low trust in official sources of information.
These interactive figures identify communities across Maine that are most most vulnerable to the risks of inland flooding or coastal storm surge.
Map of Census block groups with the highest concentrations of one or more priority populations living in FEMA flood zones.
Map of Census block groups with the highest concentrations of one or more priority populations living in hurricane evacuation zones.
These maps show communities (i.e. Census Block Groups) with high percentages of one or more priority population groups (80th percentile for the state) AND that are living within flood risk zones or hurricane evacuation zones.
The analysis of flood exposure presented here is based on the Federal Emergency Management Agency’s (FEMA) National Flood Hazard Layer (NFHL), a digital version of FEMA’s most recent flood maps. Flood risk areas are subject to floods with an Annual Exceedance Probability (AEP) of 1% (also known as a ‘100-year’ flood) and areas subject to 0.2% AEP (also known as a ‘500-year’ flood). Areas within the 1% AEP flood zone are designated by FEMA as Special Flood Hazard Areas, and development within those zones must be covered by flood insurance. Areas within the 0.2% AEP are not currently regulated, but these areas are nevertheless subject to flood risk under more extreme, albeit less frequent, flooding circumstances.
Note that digital data on flood risk for most of northern Maine, as well as the southeast corner, is not currently available from FEMA. Flood risk for these areas is likely to be underestimated.
The analysis of hurricane evacuation risk presented here is based on Hurricane Evacuation Maps produced by the U.S. Army Corps of Engineers for New England. The maps show Hurricane Evacuation Zones that are recommended to be evacuated during potential worst-case hurricane storm surge inundation. These evacuation zones are based on storm surge modeling by the National Weather Service’s National Hurricane Center using the hydrodynamic Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model to simulate storm surge from tropical cyclones.
Priority populations represent demographic groups that environmental justice policy and research have identified as being especially vulnerable to environmental burdens as a consequence of social or economic disadvantage, physical vulnerability, or historic and persistent discrimination and inequality. These include:
Identifying populations at risk:
The highlighted areas at risk in the maps represent entire Census block groups. Please note, however, that not all of the Census block group is necessarily at risk of flooding or hurricane evacuation. The analysis identified only those developed or occupied portions of block groups falling within flood zones or hurricane evacuation zones based on ancillary data from the National Land Cover Database (NLCD). The NLCD is a nationwide geospatial database on land cover and land cover change at a 30m resolution produced by the US Geological Survey (USGS) in partnership with several federal agencies as part of the Multi-Resolution Land Characteristics Consortium (MRLC). Entire Census block groups are presented in these maps for ease of visualization at the scale of the state. Please consult the supporting Technical Report for this analysis for more detailed figures and tables.
Percentage of priority populations living within FEMA flood zones.
Maine Populations Living within Hurricane Inundation Zones.
These graphs show population-weighted flood risk or hurricane evacuation exposure by group:
Note that digital data on flood risk for most of northern Maine, as well as the southeast corner, is not currently available from FEMA. Flood risk for these areas is likely to be underestimated.
Identifying populations at risk:
In order to identify counts and percentages of populations at risk, polygons of flood or hurricane evacuation risk zones were spatially intersected with the developed or occupied portions of block groups based on ancillary data from the National Land Cover Database (NLCD). The NLCD is a nationwide geospatial database on land cover and land cover change at a 30m resolution produced by the US Geological Survey (USGS) in partnership with several federal agencies as part of the Multi-Resolution Land Characteristics Consortium (MRLC). Populations at risk were calculated based on a process of areal apportionment. The population at risk from flooding was calculated as the product of the areal proportion of the intersecting flood and developed Block Group polygons: Population at risk = Proportion of developed Block Group Intersection x Population of developed Block Group For example, if 10% of the developed area of a Census Block Group intersected/overlapped with a flood polygon, it was assumed that 10% of the population is exposed to that flood risk. Assuming a population of 100 people in the developed portion of the Block Group, this would mean 100 x .10 = 10 people would be subject to flood risk.
These tables show the number and percentage of the general population by jurisdiction exposed to FEMA flood risk or hurricane evacuation risk. FEMA flood risk is calculated as the percentage of a Census block group that falls within 100-year or 500-year flood risk zones and aggregated by jurisdiction. Hurricane evacuation risk is calculated as the percentage of a Census block group that falls within hurricane evacuation zones identified by the Maine Emergency Management Agency and U.S. Army Corps of Engineers, and aggregated by jurisdiction. Population values are derived from the American Community Survey 5-year estimates for 2014-2018.
Note that digital data on flood risk for most of northern Maine, as well as the southeast corner, is not currently available from FEMA. Flood risk for these areas is likely to be underestimated.
Identifying populations at risk:
In order to identify counts and percentages of populations at risk, polygons of flood or hurricane evacuation risk zones were spatially intersected with the developed or occupied portions of block groups based on ancillary data from the National Land Cover Database (NLCD). The NLCD is a nationwide geospatial database on land cover and land cover change at a 30m resolution produced by the US Geological Survey (USGS) in partnership with several federal agencies as part of the Multi-Resolution Land Characteristics Consortium (MRLC). Populations at risk were calculated based on a process of areal apportionment. The population at risk from flooding was calculated as the product of the areal proportion of the intersecting flood and developed Block Group polygons: Population at risk = Proportion of developed Block Group Intersection x Population of developed Block Group For example, if 10% of the developed area of a Census Block Group intersected/overlapped with a flood polygon, it was assumed that 10% of the population is exposed to that flood risk. Assuming a population of 100 people in the developed portion of the Block Group, this would mean 100 x .10 = 10 people would be subject to flood risk.