Mercer County, Pennsylvania Natural Disaster Risk
FEMA National Risk Index assessment · PA
LowComposite Risk Score
National percentile: 78th
Mercer County faces low composite natural disaster risk (NRI Risk Index score 77.7, 78th national percentile), driven primarily by riverine flood and lightning exposure. Expected annual loss across all 18 hazard types is $34M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
FEMA's National Risk Index rates Mercer County at low composite risk, with a National Risk Index score of 77.7 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.
Most of Mercer County's expected losses come from riverine flood (rivers and streams overflowing their banks after heavy rain or snowmelt) at Medium risk — $29M in expected annual loss and about 2.50 events per year; lightning (electrical discharges from storms that ignite fires and cause casualties) at High risk — $926K in expected annual loss and about 39.56 events per year; and winter weather (heavy snow, blizzards, and hazardous winter conditions) at Medium risk — $168K in expected annual loss and about 16.84 events per year. Across all hazards, FEMA estimates $34M in expected annual loss for a population of 111K.
Beyond physical exposure, Mercer County has a medium social vulnerability rating (how susceptible the population is to harm) and a 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.
The federal record bears this out: Mercer County has received 13 federal disaster declarations since 1972, including 3 for hurricane events and 3 for flood events. The most recent was Covid-19 Pandemic (biological), declared in March 2020.
Among 67 Pennsylvania counties, Mercer County ranks #27 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Riverine Flood | Medium | 2.50 / yr | $29M |
| Lightning | High | 39.56 / yr | $926K |
| Winter Weather | Medium | 16.84 / yr | $168K |
| Hail | Medium | 3.79 / yr | $647K |
| Strong Wind | Medium | 2.28 / yr | $981K |
| Hurricane | Low | 0.02 / yr | $306K |
| Tornado | Low | 0.28 / yr | $1M |
| Earthquake | Very Low | 0.00 / yr | $269K |
| Landslide | Very Low | 0.20 / yr | $737 |
| Ice Storm | Low | 0.45 / yr | $53K |
| Wildfire | Very Low | 0.00 / yr | $19K |
| Heat Wave | Very Low | 1.05 / yr | $110K |
| Cold Wave | Very Low | 3.63 / yr | $255K |
| Avalanche | Very Low | 0.00 / yr | $0 |
| Coastal Flood | Very Low | 0.00 / yr | $0 |
| Drought | Very Low | 0.00 / yr | $0 |
| Tsunami | Very Low | 0.00 / yr | $0 |
| Volcanic Activity | Very Low | 0.00 / yr | $0 |
Disaster History
Mercer County has received 13 federal disaster declarations since 1972, most recently Covid-19 Pandemic in March 2020. Most frequent causes: Hurricane (3), Flood (3), Biological (2).
| Declared | Type | Disaster |
|---|---|---|
| March 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| October 2012 | Hurricane | Hurricane Sandy |
| September 2005 | Hurricane | Hurricane Katrina |
| September 2004 | Severe Storm | Severe Storms and Flooding Associated with Tropical Depression Frances |
| September 2004 | Hurricane | Tropical Depression Ivan |
| August 2003 | Severe Storm | Severe Storms, Tornadoes, and Flooding |
| January 1996 | Flood | Severe Storms and Flooding |
| March 1993 | Snowstorm | Severe Snowfall & Winter Storm |
| June 1985 | Tornado | Severe Storms, High Winds & Tornadoes |
Showing the 10 most recent of 13 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for Mercer County?
Mercer County has a composite FEMA National Risk Index score of 77.7 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 Mercer County?
The three highest-rated hazards are Riverine Flood (Medium, $29M EAL), Lightning (High, $926K EAL), Winter Weather (Medium, $168K EAL). These account for most of the county's expected annual losses.
How does Mercer County compare to other Pennsylvania counties?
Mercer County ranks #27 of 67 Pennsylvania counties for overall natural disaster risk, with a low rating.
How many federally declared disasters has Mercer County had?
FEMA records 13 federal disaster declarations for Mercer County since 1972, most often 3 for hurricane events and 3 for flood events. The most recent was Covid-19 Pandemic, declared in March 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. Mercer County's $34M EAL is a statistical average, not a guarantee for any specific year or address.