How will FEMA’s Pending Changes to Flood Hazard Maps Impact the Monadnock Region?

• February 6, 2026
• Natural Resources, Transportation

The Federal Emergency Management Agency’s (FEMA) Flood Insurance Rate Maps (FIRMS) are critical for helping government officials and residents understand local and regional flood risks.  The maps provide guidance to homeowners and insurance carriers on flood risk, inform towns and developers where it is safe to build or where flood mitigation measures may be required, and informs hazard mitigation planning to mention just a few of the maps’ uses. Presently, flood maps in the Monadnock Region informing flood insurance rates and regulating development in flood prone areas were finalized between 2006 and 2009, but that’s all about to change.  FEMA is required to reassess its flood maps periodically, and flood zone designations are revised when new and more accurate information becomes available. Since 2022, FEMA has been releasing new Preliminary Flood Maps for the Monadnock Region.  Presently, communities are reviewing the preliminary flood maps and given the opportunity to provide feedback on the maps, including requests for changes.  For some more information about the process for updating maps, visit this NH Department of Business and Economic Affairs webpage. 

Since new maps have been released for most of the SWRPC planning district, SWRPC has begun a regional-scale cursory analysis comparing the current FIRMS with the new Preliminary National Flood Hazard FIRMS¹. In addition, SWRPC has taken a Regional look at the overlap between the Preliminary FIRMS and existing roads, bridges, buildings, and community anchor institutions (e.g. town halls, libraries, municipal buildings, etc.) to provide some initial insight into any new flood risks facing these assets. The following analysis is based on flood plain data associated with the 34 communities representing the SWPRC planning district. At a high level, FEMA designates flood risk with three different categories: Floodways, 1% Annual Flood Risk, and 0.2% Annual Flood Risk. Floodways refer to land that is either in the channel of a river or stream or adjacent land which should be expected to flood regularly and therefore should not be developed. 1% Annual Flood Risk zones have a 1-in-100 chance of being flooded in a given year and represent high-risk zones for development; over a 30-year mortgage, 1% Annual Flood Risk zones have a 26% probability of experiencing flooding. 0.2% Annual Flood Risk zones have a 1-in-500 chance of experiencing a flood in a given year.

Across the Region, the total amount of acreage having some form of flood risk has increased by 14,099 acres when comparing the old FIRMS to the new Preliminary FIRMS. The most significant changes between the datasets are increases in land determined to having a 0.2% or 1% Annual Flood Risk, which increased by approximately 10,000 and 8,000 acres respectively. While these areas increased, the amount of land categorized as a floodway decreased by 3,728 acres. These floodway changes happened primarily along the Ashuelot and Connecticut Rivers, and to a lesser extent, the Contoocook River. Some of the floodway areas were reclassified as new 0.2% Annual Flood Hazard areas, however, this was not universal.

Despite a significant increase in the total amount of Flood Hazard Area overall in the Preliminary FIRMs, the amount of Preliminary FIRM overlap with assets such as roads, bridges, community anchor institutions, and buildings in the Monadnock Region remains relatively similar with the public data. In some cases, there is less overlap. The trends are inconsistent across the range of assets. For example, more bridges were determined to fall within the Preliminary FIRMs, as were a larger number of individual buildings. This is also true for Community Anchor Institutions. However, there is a greater amount of road mileage overlapping with the Public FIRMs than the Preliminary FIRMs.

Investigating the trends regarding the assets datasets becomes more complicated when considering the relationships established with specific Flood Zones. The Preliminary FIRMs have nearly 10,000 additional acres of area considered a 0.2% Annual Flood Risk (a 3.1x increase from the Public dataset) as well as approximately 8,000 more acres of 1% Annual Flood Risk area (1.2x increase), so it is unsurprising that the degree of overlap with these zones is greater, particularly for the 0.2% Annual Zone. For roadways, bridges, buildings, and community anchor institutions, overlap with the 0.2% Annual Flood Risk zone was found to be greater for all assets. The only exception was the building area as opposed to individual buildings. Confoundingly, despite the Preliminary FIRMs containing 1.2 times more 1% Annual Flood Risk Area, the number of assets of overlapping with this zone is greater in the Public dataset. Further analysis will be conducted to better understand this discrepancy.

For more information about FEMA’s Preliminary Flood Hazard Zones, or about this GIS analysis, please contact Jason Cooper of SWRPC staff at [email protected].