Lyman County, South Dakota Natural Disaster Risk
FEMA National Risk Index assessment · SD
Very LowComposite Risk Score
National percentile: 26th
Lyman County faces very low composite natural disaster risk (NRI Risk Index score 26.5, 26th national percentile), driven primarily by cold wave and wildfire exposure. Expected annual loss across all 18 hazard types is $6M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
Overall natural disaster risk in Lyman County is very low, with a National Risk Index score of 26.5 out of 100 — placing it in the 26th 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 cold wave (prolonged spells of dangerously low temperatures) at Medium risk — $2M in expected annual loss and about 5.74 events per year; wildfire (uncontrolled fires that spread across wildland and into communities) at Low risk — $115K in expected annual loss and about 0.00 events per year; and winter weather (heavy snow, blizzards, and hazardous winter conditions) at Medium risk — $86K in expected annual loss and about 16.42 events per year. Across all hazards, FEMA estimates $6M in expected annual loss for a population of 4K.
Beyond physical exposure, Lyman County has a very high social vulnerability rating (how susceptible the population is to harm) and a 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.
History supports the rating: Lyman County has received 16 federal disaster declarations since 1976, including 7 for flood events and 4 for severe storm events. The most recent was Covid-19 Pandemic (biological), declared in April 2020.
Among 66 South Dakota counties, Lyman County ranks #28 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Cold Wave | Medium | 5.74 / yr | $2M |
| Wildfire | Low | 0.00 / yr | $115K |
| Winter Weather | Medium | 16.42 / yr | $86K |
| Hail | Low | 3.69 / yr | $367K |
| Drought | Low | 33.48 / yr | $144K |
| Ice Storm | Low | 0.38 / yr | $32K |
| Riverine Flood | Very Low | 1.14 / yr | $2M |
| Tornado | Low | 0.57 / yr | $297K |
| Heat Wave | Very Low | 4.89 / yr | $53K |
| Landslide | Very Low | 0.51 / yr | $98 |
| Strong Wind | Very Low | 2.76 / yr | $91K |
| Earthquake | Very Low | 0.00 / yr | $9K |
| Lightning | Very Low | 35.73 / yr | $24K |
| 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
Lyman County has received 16 federal disaster declarations since 1976, most recently Covid-19 Pandemic in April 2020. Most frequent causes: Flood (7), Severe Storm (4), Biological (2).
| Declared | Type | Disaster |
|---|---|---|
| April 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| September 2019 | Flood | Severe Storms and Flooding |
| June 2019 | Flood | Severe Winter Storm, Snowstorm, and Flooding |
| July 2015 | Severe Storm | Severe Storms, Tornadoes, Straight-Line Winds, and Flooding |
| May 2011 | Flood | Flooding |
| May 2010 | Flood | Flooding |
| March 2010 | Severe Storm | Severe Winter Storm and Snowstorm |
| July 2008 | Severe Storm | Severe Storms and Flooding |
| September 2005 | Coastal Storm | Hurricane Katrina Evacuation |
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 Lyman County?
Lyman County has a composite FEMA National Risk Index score of 26.5 out of 100, placing it in the Very Low category and the 26th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in Lyman County?
The three highest-rated hazards are Cold Wave (Medium, $2M EAL), Wildfire (Low, $115K EAL), Winter Weather (Medium, $86K EAL). These account for most of the county's expected annual losses.
How does Lyman County compare to other South Dakota counties?
Lyman County ranks #28 of 66 South Dakota counties for overall natural disaster risk, with a very low rating.
How many federally declared disasters has Lyman County had?
FEMA records 16 federal disaster declarations for Lyman County since 1976, most often 7 for flood events and 4 for severe storm 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. Lyman County's $6M EAL is a statistical average, not a guarantee for any specific year or address.