Flood and fluvial erosion are significant risks in Vermont. In the event of extensive 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 Vermont 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 or river corridors.
This map shows 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 FEMA flood risk zones OR River Corridors.
The analysis of FEMA 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 much of northern Vermont is not currently available from FEMA. FEMA flood risk for northern Vermont is likely to be underestimated.
The analysis of exposure to River Corridors is based on maps produced by the Vermont Agency of Natural Resources (ANR). The ANR’s river corridors represent areas surrounding a river that allow for the meandering, floodplain, and the riparian functions necessary to restore and maintain the naturally stable or least erosive form of a river in order to minimize erosion hazards over time. Lands within and immediately abutting a river corridor are at higher risk to fluvial erosion. Damage surveys in Vermont have shown that fluvial erosion, not inundation, is the most common natural hazard type in Vermont.
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 river corridors. The analysis identified only those developed or occupied portions of block groups falling within flood zones or river corridors 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 or River Corridors.
This graph shows population-weighted flood risk or river corridor exposure by group:
Note that digital data on flood risk for much of northern Vermont is not currently available from FEMA. FEMA flood risk for northern Vermont is likely to be underestimated.
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:
In order to identify counts and percentages of populations at risk, polygons of flood or river corridor 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 river corridors.
Note that digital data on flood risk for much of northern Vermont is not currently available from FEMA. FEMA flood risk for northern Vermont is likely to be underestimated.
Identifying populations at risk:
In order to identify counts and percentages of populations at risk, polygons of flood or river corridor 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.