Johnson County, Iowa Natural Disaster Risk
FEMA National Risk Index assessment · IA
MediumComposite Risk Score
National percentile: 87th
Johnson County faces medium composite natural disaster risk (NRI Risk Index score 87.4, 87th national percentile), driven primarily by strong wind and tornado exposure. Expected annual loss across all 18 hazard types is $96M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
Overall natural disaster risk in Johnson County is medium, with a National Risk Index score of 87.4 out of 100 — placing it in the 87th 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.
Risk here concentrates in strong wind (damaging straight-line winds outside of tornadoes and hurricanes) at Very High risk — $10M in expected annual loss and about 6.41 events per year; tornado (violently rotating columns of air capable of catastrophic local damage) at High risk — $36M in expected annual loss and about 0.59 events per year; and hail (ice stones from severe thunderstorms that damage property and crops) at High risk — $4M in expected annual loss and about 4.44 events per year. Across all hazards, FEMA estimates $96M in expected annual loss for a population of 153K.
Beyond physical exposure, Johnson 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: Johnson County has received 24 federal disaster declarations since 1965, including 12 for flood events and 7 for severe storm events. The most recent was Severe Storms (severe storm), declared in August 2020.
Among 99 Iowa counties, Johnson County ranks #2 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Strong Wind | Very High | 6.41 / yr | $10M |
| Tornado | High | 0.59 / yr | $36M |
| Hail | High | 4.44 / yr | $4M |
| Cold Wave | High | 7.16 / yr | $10M |
| Winter Weather | High | 15.53 / yr | $492K |
| Heat Wave | Medium | 7.00 / yr | $4M |
| Drought | Medium | 12.89 / yr | $1M |
| Riverine Flood | Medium | 1.96 / yr | $27M |
| Landslide | Low | 0.20 / yr | $20K |
| Ice Storm | Medium | 0.46 / yr | $428K |
| Lightning | Medium | 44.31 / yr | $830K |
| Wildfire | Low | 0.00 / yr | $164K |
| Earthquake | Very Low | 0.00 / yr | $294K |
| Hurricane | Very Low | 0.01 / yr | $5K |
| Avalanche | Very Low | 0.00 / yr | $0 |
| 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
Johnson County has received 24 federal disaster declarations since 1965, most recently Severe Storms in August 2020. Most frequent causes: Flood (12), Severe Storm (7), Biological (2).
| Declared | Type | Disaster |
|---|---|---|
| August 2020 | Severe Storm | Severe Storms |
| March 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| August 2014 | Severe Storm | Severe Storms, Tornadoes, Straight-Line Winds, and Flooding |
| July 2013 | Severe Storm | Severe Storms, Tornadoes, and Flooding |
| May 2013 | Flood | Severe Storms, Straight-Line Winds, and Flooding |
| May 2008 | Severe Storm | Severe Storms, Tornadoes, and Flooding |
| January 2008 | Severe Ice Storm | Severe Winter Storm |
| March 2007 | Severe Storm | Severe Winter Storms |
| September 2005 | Hurricane | Hurricane Katrina Evacuation |
Showing the 10 most recent of 24 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for Johnson County?
Johnson County has a composite FEMA National Risk Index score of 87.4 out of 100, placing it in the Medium category and the 87th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Johnson County?
The three highest-rated hazards are Strong Wind (Very High, $10M EAL), Tornado (High, $36M EAL), Hail (High, $4M EAL). These account for most of the county's expected annual losses.
How does Johnson County compare to other Iowa counties?
Johnson County ranks #2 of 99 Iowa counties for overall natural disaster risk, with a medium rating.
How many federally declared disasters has Johnson County had?
FEMA records 24 federal disaster declarations for Johnson County since 1965, most often 12 for flood events and 7 for severe storm events. The most recent was Severe Storms, declared in August 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. Johnson County's $96M EAL is a statistical average, not a guarantee for any specific year or address.