Brown County, South Dakota Natural Disaster Risk
FEMA National Risk Index assessment · SD
LowComposite Risk Score
National percentile: 74th
Brown County faces low composite natural disaster risk (NRI Risk Index score 73.5, 74th national percentile), driven primarily by winter weather and cold wave exposure. Expected annual loss across all 18 hazard types is $37M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
Overall natural disaster risk in Brown County is low, with a National Risk Index score of 73.5 out of 100 — placing it in the 74th 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.
Risk here concentrates in winter weather (heavy snow, blizzards, and hazardous winter conditions) at Very High risk — $2M in expected annual loss and about 20.11 events per year; cold wave (prolonged spells of dangerously low temperatures) at High risk — $16M in expected annual loss and about 13.37 events per year; and hail (ice stones from severe thunderstorms that damage property and crops) at Medium risk — $2M in expected annual loss and about 3.88 events per year. Across all hazards, FEMA estimates $37M in expected annual loss for a population of 38K.
Beyond physical exposure, Brown County has a 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.
History supports the rating: Brown County has received 19 federal disaster declarations since 1969, including 9 for flood events and 6 for severe storm events. The most recent was Flooding (flood), declared in July 2023.
Among 66 South Dakota counties, Brown County ranks #4 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Winter Weather | Very High | 20.11 / yr | $2M |
| Cold Wave | High | 13.37 / yr | $16M |
| Hail | Medium | 3.88 / yr | $2M |
| Strong Wind | Medium | 2.61 / yr | $2M |
| Ice Storm | Medium | 0.37 / yr | $534K |
| Wildfire | Low | 0.00 / yr | $353K |
| Tornado | Medium | 0.80 / yr | $3M |
| Riverine Flood | Low | 5.18 / yr | $11M |
| Heat Wave | Low | 3.63 / yr | $402K |
| Landslide | Very Low | 0.16 / yr | $1K |
| Drought | Very Low | 2.45 / yr | $31K |
| Earthquake | Very Low | 0.00 / yr | $68K |
| Lightning | Very Low | 31.78 / yr | $27K |
| 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
Brown County has received 19 federal disaster declarations since 1969, most recently Flooding in July 2023. Most frequent causes: Flood (9), Severe Storm (6), Biological (2).
| Declared | Type | Disaster |
|---|---|---|
| July 2023 | Flood | Flooding |
| April 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| June 2019 | Flood | Severe Winter Storm, Snowstorm, and Flooding |
| May 2011 | Flood | Flooding |
| May 2010 | Flood | Flooding |
| June 2009 | Severe Storm | Severe Storms and Flooding |
| May 2007 | Severe Storm | Severe Storms, Tornadoes, and Flooding |
| December 2005 | Severe Storm | Severe Winter Storm |
| September 2005 | Coastal Storm | Hurricane Katrina Evacuation |
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 Brown County?
Brown County has a composite FEMA National Risk Index score of 73.5 out of 100, placing it in the Low category and the 74th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Brown County?
The three highest-rated hazards are Winter Weather (Very High, $2M EAL), Cold Wave (High, $16M EAL), Hail (Medium, $2M EAL). These account for most of the county's expected annual losses.
How does Brown County compare to other South Dakota counties?
Brown County ranks #4 of 66 South Dakota counties for overall natural disaster risk, with a low rating.
How many federally declared disasters has Brown County had?
FEMA records 19 federal disaster declarations for Brown County since 1969, most often 9 for flood events and 6 for severe storm events. The most recent was Flooding, declared in July 2023.
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. Brown County's $37M EAL is a statistical average, not a guarantee for any specific year or address.