Chester County, Pennsylvania Natural Disaster Risk
FEMA National Risk Index assessment · PA
MediumComposite Risk Score
National percentile: 92th
Chester County faces medium composite natural disaster risk (NRI Risk Index score 91.9, 92th national percentile), driven primarily by drought and winter weather exposure. Expected annual loss across all 18 hazard types is $173M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
Overall natural disaster risk in Chester County is medium, with a National Risk Index score of 91.9 out of 100 — placing it in the 92nd national percentile and near the national midpoint for natural-disaster risk. The score blends Expected Annual Loss, Social Vulnerability, and Community Resilience across all 18 FEMA hazard types.
Most of Chester County's expected losses come from drought (extended dry periods that stress water supplies and agriculture) at High risk — $10M in expected annual loss and about 4.93 events per year; winter weather (heavy snow, blizzards, and hazardous winter conditions) at Very High risk — $2M in expected annual loss and about 12.13 events per year; and heat wave (prolonged periods of extreme heat that threaten health and infrastructure) at Medium risk — $11M in expected annual loss and about 9.18 events per year. Across all hazards, FEMA estimates $173M in expected annual loss for a population of 534K.
Beyond physical exposure, Chester 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.
The county's disaster history tells the same story: Chester County has received 26 federal disaster declarations since 1965, including 7 for hurricane events and 6 for flood events. The most recent was Remnants of Hurricane Ida (hurricane), declared in September 2021.
Among 67 Pennsylvania counties, Chester County ranks #9 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Drought | High | 4.93 / yr | $10M |
| Winter Weather | Very High | 12.13 / yr | $2M |
| Heat Wave | Medium | 9.18 / yr | $11M |
| Strong Wind | High | 7.21 / yr | $5M |
| Riverine Flood | High | 5.46 / yr | $106M |
| Lightning | High | 35.75 / yr | $2M |
| Earthquake | Medium | 0.00 / yr | $8M |
| Hurricane | Medium | 0.08 / yr | $10M |
| Tornado | Medium | 0.45 / yr | $10M |
| Ice Storm | High | 1.33 / yr | $993K |
| Cold Wave | Medium | 0.92 / yr | $8M |
| Landslide | Low | 0.66 / yr | $20K |
| Hail | Low | 2.76 / yr | $618K |
| Wildfire | Very Low | 0.00 / yr | $23K |
| Avalanche | Very Low | 0.00 / yr | $0 |
| Coastal Flood | Very Low | 0.01 / yr | $0 |
| Tsunami | Very Low | 0.00 / yr | $0 |
| Volcanic Activity | Very Low | 0.00 / yr | $0 |
Disaster History
Chester County has received 26 federal disaster declarations since 1965, most recently Remnants of Hurricane Ida in September 2021. Most frequent causes: Hurricane (7), Flood (6), Severe Storm (5).
| Declared | Type | Disaster |
|---|---|---|
| September 2021 | Hurricane | Remnants of Hurricane Ida |
| March 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| March 2016 | Snowstorm | Severe Winter Storm and Snowstorm |
| February 2014 | Severe Ice Storm | Severe Winter Storm |
| October 2012 | Hurricane | Hurricane Sandy |
| September 2011 | Flood | Tropical Storm Lee |
| September 2011 | Flood | Remnants of Tropical Storm Lee |
| September 2011 | Hurricane | Hurricane Irene |
| August 2011 | Hurricane | Hurricane Irene |
Showing the 10 most recent of 26 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for Chester County?
Chester County has a composite FEMA National Risk Index score of 91.9 out of 100, placing it in the Medium category and the 92th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Chester County?
The three highest-rated hazards are Drought (High, $10M EAL), Winter Weather (Very High, $2M EAL), Heat Wave (Medium, $11M EAL). These account for most of the county's expected annual losses.
How does Chester County compare to other Pennsylvania counties?
Chester County ranks #9 of 67 Pennsylvania counties for overall natural disaster risk, with a medium rating.
How many federally declared disasters has Chester County had?
FEMA records 26 federal disaster declarations for Chester County since 1965, most often 7 for hurricane events and 6 for flood events. The most recent was Remnants of Hurricane Ida, declared in September 2021.
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. Chester County's $173M EAL is a statistical average, not a guarantee for any specific year or address.