Merrimack County, New Hampshire Natural Disaster Risk
FEMA National Risk Index assessment · NH
LowComposite Risk Score
National percentile: 78th
Merrimack County faces low composite natural disaster risk (NRI Risk Index score 78.2, 78th national percentile), driven primarily by ice storm and lightning exposure. Expected annual loss across all 18 hazard types is $49M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
FEMA's National Risk Index rates Merrimack County at low composite risk, with a National Risk Index score of 78.2 out of 100 — placing it in the 78th national percentile and below the national average for natural-disaster risk. The score blends Expected Annual Loss, Social Vulnerability, and Community Resilience across all 18 FEMA hazard types.
Risk here concentrates in ice storm (freezing rain that coats surfaces in heavy, damaging ice) at High risk — $1M in expected annual loss and about 1.84 events per year; lightning (electrical discharges from storms that ignite fires and cause casualties) at High risk — $1M in expected annual loss and about 20.57 events per year; and riverine flood (rivers and streams overflowing their banks after heavy rain or snowmelt) at Medium risk — $34M in expected annual loss and about 2.61 events per year. Across all hazards, FEMA estimates $49M in expected annual loss for a population of 154K.
Beyond physical exposure, Merrimack County has a very low social vulnerability rating (how susceptible the population is to harm) and a very high community resilience rating (its capacity to prepare for and recover from disasters). A less vulnerable population paired with strong resilience helps the community absorb and recover from events.
History supports the rating: Merrimack County has received 29 federal disaster declarations since 1973, including 12 for severe storm events and 5 for snowstorm events. The most recent was Covid-19 Pandemic (biological), declared in April 2020.
Among 10 New Hampshire counties, Merrimack County ranks #4 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Ice Storm | High | 1.84 / yr | $1M |
| Lightning | High | 20.57 / yr | $1M |
| Riverine Flood | Medium | 2.61 / yr | $34M |
| Hurricane | Medium | 0.09 / yr | $4M |
| Landslide | Low | 1.29 / yr | $23K |
| Winter Weather | Medium | 19.13 / yr | $268K |
| Earthquake | Low | 0.00 / yr | $2M |
| Heat Wave | Low | 3.42 / yr | $1M |
| Drought | Low | 2.15 / yr | $329K |
| Tornado | Low | 0.13 / yr | $2M |
| Cold Wave | Low | 1.74 / yr | $1M |
| Strong Wind | Medium | 0.91 / yr | $748K |
| Hail | Low | 2.12 / yr | $202K |
| Wildfire | Very Low | 0.00 / yr | $24K |
| Avalanche | Very Low | 0.01 / yr | $119 |
| Coastal Flood | Very Low | 0.00 / yr | $0 |
| Tsunami | Very Low | 0.00 / yr | $0 |
| Volcanic Activity | Very Low | 0.00 / yr | $0 |
Disaster History
Merrimack County has received 29 federal disaster declarations since 1973, most recently Covid-19 Pandemic in April 2020. Most frequent causes: Severe Storm (12), Snowstorm (5), Flood (5).
| Declared | Type | Disaster |
|---|---|---|
| April 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| January 2018 | Severe Storm | Severe Storm and Flooding |
| March 2013 | Severe Storm | Severe Winter Storm and Snowstorm |
| October 2012 | Hurricane | Hurricane Sandy |
| November 2011 | Severe Storm | Severe Storm |
| September 2011 | Hurricane | Tropical Storm Irene |
| August 2011 | Hurricane | Hurricane Irene |
| March 2010 | Severe Storm | Severe Winter Storm |
| January 2009 | Severe Ice Storm | Severe Winter Storm |
Showing the 10 most recent of 29 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for Merrimack County?
Merrimack County has a composite FEMA National Risk Index score of 78.2 out of 100, placing it in the Low category and the 78th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Merrimack County?
The three highest-rated hazards are Ice Storm (High, $1M EAL), Lightning (High, $1M EAL), Riverine Flood (Medium, $34M EAL). These account for most of the county's expected annual losses.
How does Merrimack County compare to other New Hampshire counties?
Merrimack County ranks #4 of 10 New Hampshire counties for overall natural disaster risk, with a low rating.
How many federally declared disasters has Merrimack County had?
FEMA records 29 federal disaster declarations for Merrimack County since 1973, most often 12 for severe storm events and 5 for snowstorm events. The most recent was Covid-19 Pandemic, declared in April 2020.
What does Expected Annual Loss (EAL) mean?
EAL is FEMA's estimate of average annual dollar losses from natural hazards, calculated from historical event data and exposure models. Merrimack County's $49M EAL is a statistical average, not a guarantee for any specific year or address.