Union County, South Dakota Natural Disaster Risk
FEMA National Risk Index assessment · SD
Very LowComposite Risk Score
National percentile: 37th
Union County faces very low composite natural disaster risk (NRI Risk Index score 37.1, 37th national percentile), driven primarily by wildfire and winter weather exposure. Expected annual loss across all 18 hazard types is $16M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
Overall natural disaster risk in Union County is very low, with a National Risk Index score of 37.1 out of 100 — placing it in the 37th national percentile and among the lowest-risk counties in the country. The score blends Expected Annual Loss, Social Vulnerability, and Community Resilience across all 18 FEMA hazard types.
Risk here concentrates in wildfire (uncontrolled fires that spread across wildland and into communities) at Low risk — $447K in expected annual loss and about 0.00 events per year; winter weather (heavy snow, blizzards, and hazardous winter conditions) at Medium risk — $256K in expected annual loss and about 15.42 events per year; and drought (extended dry periods that stress water supplies and agriculture) at Medium risk — $951K in expected annual loss and about 27.26 events per year. Across all hazards, FEMA estimates $16M in expected annual loss for a population of 17K.
Beyond physical exposure, Union County has a very low social vulnerability rating (how susceptible the population is to harm) and a medium community resilience rating (its capacity to prepare for and recover from disasters). Both measures sit toward the lower end, indicating relatively modest population sensitivity.
The county's disaster history tells the same story: Union County has received 19 federal disaster declarations since 1969, including 9 for flood events and 6 for severe storm events. The most recent was Severe Storms, Straight-Line Winds, and Flooding (flood), declared in August 2024.
Among 66 South Dakota counties, Union County ranks #21 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Wildfire | Low | 0.00 / yr | $447K |
| Winter Weather | Medium | 15.42 / yr | $256K |
| Drought | Medium | 27.26 / yr | $951K |
| Hail | Medium | 6.45 / yr | $917K |
| Tornado | Medium | 0.40 / yr | $3M |
| Ice Storm | Medium | 0.98 / yr | $272K |
| Riverine Flood | Low | 3.61 / yr | $9M |
| Landslide | Very Low | 0.08 / yr | $670 |
| Cold Wave | Low | 6.47 / yr | $734K |
| Heat Wave | Very Low | 6.47 / yr | $234K |
| Lightning | Low | 39.68 / yr | $164K |
| Strong Wind | Low | 4.09 / yr | $346K |
| Earthquake | Very Low | 0.00 / yr | $28K |
| 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
Union County has received 19 federal disaster declarations since 1969, most recently Severe Storms, Straight-Line Winds, and Flooding in August 2024. Most frequent causes: Flood (9), Severe Storm (6), Biological (2).
| Declared | Type | Disaster |
|---|---|---|
| August 2024 | Flood | Severe Storms, Straight-Line Winds, and Flooding |
| April 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| November 2019 | Severe Storm | Severe Storms, Tornadoes, and Flooding |
| September 2019 | Flood | Severe Storms and Flooding |
| June 2019 | Flood | Severe Winter Storm, Snowstorm, and Flooding |
| July 2014 | Flood | Severe Storms, Tornadoes, and Flooding |
| June 2013 | Severe Storm | Severe Storms, Tornado, and Flooding |
| May 2011 | Flood | Flooding |
| November 2010 | Severe Storm | Severe Storms and Flooding |
Showing the 10 most recent of 19 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for Union County?
Union County has a composite FEMA National Risk Index score of 37.1 out of 100, placing it in the Very Low category and the 37th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Union County?
The three highest-rated hazards are Wildfire (Low, $447K EAL), Winter Weather (Medium, $256K EAL), Drought (Medium, $951K EAL). These account for most of the county's expected annual losses.
How does Union County compare to other South Dakota counties?
Union County ranks #21 of 66 South Dakota counties for overall natural disaster risk, with a very low rating.
How many federally declared disasters has Union County had?
FEMA records 19 federal disaster declarations for Union County since 1969, most often 9 for flood events and 6 for severe storm events. The most recent was Severe Storms, Straight-Line Winds, and Flooding, declared in August 2024.
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. Union County's $16M EAL is a statistical average, not a guarantee for any specific year or address.