Dewey County, South Dakota Natural Disaster Risk
FEMA National Risk Index assessment · SD
LowComposite Risk Score
National percentile: 79th
Dewey County faces low composite natural disaster risk (NRI Risk Index score 78.7, 79th national percentile), driven primarily by cold wave and winter weather exposure. Expected annual loss across all 18 hazard types is $22M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
Dewey County carries a low composite natural disaster risk, with a National Risk Index score of 78.7 out of 100 — placing it in the 79th 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.
The county's risk is driven primarily by cold wave (prolonged spells of dangerously low temperatures) at Very High risk — $20M in expected annual loss and about 9.21 events per year; winter weather (heavy snow, blizzards, and hazardous winter conditions) at High risk — $159K in expected annual loss and about 16.58 events per year; and wildfire (uncontrolled fires that spread across wildland and into communities) at Low risk — $318K in expected annual loss and about 0.00 events per year. Across all hazards, FEMA estimates $22M in expected annual loss for a population of 5K.
Beyond physical exposure, Dewey County has a very high social vulnerability rating (how susceptible the population is to harm) and a very low community resilience rating (its capacity to prepare for and recover from disasters). That combination — a more vulnerable population with limited resilience — can amplify the human cost of any given event.
The federal record bears this out: Dewey County has received 16 federal disaster declarations since 1976, including 7 for severe storm events and 3 for flood events. The most recent was Covid-19 Pandemic (biological), declared in April 2020.
Among 66 South Dakota counties, Dewey County ranks #2 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Cold Wave | Very High | 9.21 / yr | $20M |
| Winter Weather | High | 16.58 / yr | $159K |
| Wildfire | Low | 0.00 / yr | $318K |
| Ice Storm | Medium | 0.55 / yr | $94K |
| Hail | Low | 2.85 / yr | $195K |
| Landslide | Very Low | 1.04 / yr | $201 |
| Drought | Very Low | 50.02 / yr | $11K |
| Tornado | Very Low | 0.54 / yr | $192K |
| Heat Wave | Very Low | 2.84 / yr | $47K |
| Strong Wind | Low | 2.32 / yr | $119K |
| Riverine Flood | Very Low | 0.96 / yr | $1M |
| Lightning | Very Low | 32.69 / yr | $31K |
| Earthquake | Very Low | 0.00 / yr | $7K |
| Avalanche | Very Low | 0.00 / yr | $0 |
| Coastal Flood | Very Low | 0.00 / yr | $0 |
| Hurricane | Very Low | 0.00 / yr | $0 |
| Tsunami | Very Low | 0.00 / yr | $0 |
| Volcanic Activity | Very Low | 0.00 / yr | $0 |
Disaster History
Dewey County has received 16 federal disaster declarations since 1976, most recently Covid-19 Pandemic in April 2020. Most frequent causes: Severe Storm (7), Flood (3), Biological (2).
| Declared | Type | Disaster |
|---|---|---|
| April 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| June 2019 | Flood | Severe Winter Storm, Snowstorm, and Flooding |
| February 2017 | Severe Storm | Severe Winter Storm |
| July 2014 | Flood | Severe Storms, Tornadoes, and Flooding |
| November 2013 | Severe Storm | Severe Winter Storm, Snowstorm, and Flooding |
| July 2010 | Severe Storm | Severe Storms, Tornadoes, and Flooding |
| March 2010 | Severe Storm | Severe Winter Storm |
| June 2009 | Severe Storm | Severe Storms and Flooding |
| December 2008 | Snowstorm | Severe Winter Storm and Record and Near Record Snow |
Showing the 10 most recent of 16 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for Dewey County?
Dewey County has a composite FEMA National Risk Index score of 78.7 out of 100, placing it in the Low category and the 79th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Dewey County?
The three highest-rated hazards are Cold Wave (Very High, $20M EAL), Winter Weather (High, $159K EAL), Wildfire (Low, $318K EAL). These account for most of the county's expected annual losses.
How does Dewey County compare to other South Dakota counties?
Dewey County ranks #2 of 66 South Dakota counties for overall natural disaster risk, with a low rating.
How many federally declared disasters has Dewey County had?
FEMA records 16 federal disaster declarations for Dewey County since 1976, most often 7 for severe storm events and 3 for flood 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. Dewey County's $22M EAL is a statistical average, not a guarantee for any specific year or address.