Risk-assessment baseline packet. County FIPS 46013. Release 2026-10, data as of 2026-09-30.
Summary
Plan status as of 2026-09-30: Approved, expires 2027-02-07. Plan: Brown County, SD Hazard Mitigation Plan 2022 (FEMA plan 107917), approved 2022-02-08.
Since the plan was approved on 2022-02-08: 1 new hazard declaration (1 incident) and 207 NOAA Storm Events records; details under "What changed since your last plan".
Highest expected annual loss (FEMA National Risk Index, modeled total; see B1-a): Cold Wave ($16,354,723 a year), Inland Flooding ($11,281,939) and Tornado ($2,877,156).
The packet's tables are organized by the items of FEMA's Local Mitigation Plan Review Tool, Element B (B1-a to B2-c); the summaries below follow the same order.
What the packet contains
Sections in FEMA checklist order; each heading names the review item its tables support. Full tables are in the downloads above.
Supports FEMA checklist item B1-a Hazard identification
13 of the 18 National Risk Index hazards apply here.
Not applicable to this county per NRI, with no federal declaration and no Storm Events record since 1996: avalanche, coastal flooding, tsunami and volcanic activity. That is the evidence for leaving them out of the plan.
Highest expected annual loss (NRI, modeled): Cold Wave, Inland Flooding and Tornado.
Not covered by NRI (local data needed): dam failure (incl. upstream dams); levee failure; flash flood as its own subtype; ice jams; debris flows; erosion (riverine and coastal); land subsidence and sinkholes; expansive soils.
The state hazard mitigation plan also lists hazards for this county; FEMA asks the plan to explain any hazard it leaves out.
Supports FEMA checklist item B1-b Hazard location
- Cold Wave, Drought, Hail, Heat Wave, Ice Storm, Lightning, Strong Wind and Winter Weather: affects the whole county; national data give no location within it.
- Earthquake, Hurricane, Landslide, Tornado and Wildfire vary within the county; the packet lists the highest-rated census tracts for each.
- Inland Flooding: the FEMA Flood Insurance Rate Map (FIRM) is the required location source for flooding. See the FEMA Flood Map Service Center (https://msc.fema.gov) for this county.
Supports FEMA checklist item B1-c Hazard extent
Storm Events records for 12 of the 20 NOAA event-type groups mapped to the 18 hazards, with the scale, observed range and worst recorded event for each; the others say which local data are needed.
Worst recorded tornado, hail and thunderstorm wind (the three event types on record since the 1950s; the packet has every group):
- Hail: 4.5 in hail, 2002-06-23; same size also recorded on 1987-08-15
- Thunderstorm Wind: 113 kt (130 mph) estimated gust, Thunderstorm Wind, 2022-06-14
- Tornado: F4 tornado, 2002-06-23, 9 mi within this county, 900 yd wide, damage not reported
Supports FEMA checklist item B1-d Previous occurrences
Federal declarations for this area: 19 declarations covering 16 separate hazard incidents counted in this packet; each with type, dates and county Public Assistance dollars.
New since the last plan (approved 2022-02-08): DR-4718-SD.
3 statewide declarations listed separately.
Hazards with no Storm Events record and no federal declaration are stated as such (7 of 18).
Storm Events history: 1,417 records (notable ones in the PDF, all of them in the Excel file).
Supports FEMA checklist item B1-e Probability of future events
FEMA annualized frequency (modeled) for each hazard, with a descriptor from a scale defined in the packet.
- Highly likely: Hail, Lightning and Strong Wind
- Likely: Cold Wave, Drought, Heat Wave, Ice Storm, Inland Flooding, Landslide, Tornado, Wildfire and Winter Weather
- Unlikely: Earthquake
Historical frequency by intensity band (tornado, hail, wind): 9 bands from Storm Events.
Supports FEMA checklist item B1-f Hazards that vary across jurisdictions
Range of census tract risk scores within the area for 14 of the 18 hazards (8 tracts; rated tracts only).
5 jurisdictions: plan clock, repeat-flood count, Public Assistance dollars and event records naming the place (starting figures from federal data).
County Public Assistance in B1-d also includes applicants filed under the county that are not matched to a jurisdiction row here (for example county departments filed under their own names, such as a highway department or emergency management agency, and state agencies, special districts and nonprofits), so the jurisdiction rows add up to less.
Supports FEMA checklist items B2-a and B2-b Vulnerability and potential impacts
The packet's table gives county-level starting figures; the plan describes impacts for each jurisdiction and its own assets.
Storm Events damage since 2022-02-08: $349,000 in county-coded records (139 records); $35,000 reported for the zone (68 zone records). Data through 2026-06-30; nominal dollars.
Local data needed
To gather:
- Critical facilities and lifelines per hazard
- A problem statement per jurisdiction per hazard
- Changes in development in hazard-prone areas since the last approval, or a statement of none (E1-a)
- Future assets
Supports FEMA checklist item B2-a Vulnerability (county context)
Population 38,265; building value $12,683,541,999 and agriculture value $486,006,398 (total, not at risk).
National Risk Index rating Relatively Low; social vulnerability Relatively Low; community resilience Very High.
Supports FEMA checklist item B2-c Repetitive loss properties
Repetitive-loss properties, FMA definition (44 CFR 77.2): 0 repetitive loss, 0 severe repetitive loss. NFIP insurance definition: 14 and 0.
Mitigated 0; insured 1; NFIP data as of 2026-08-02. Counts by occupancy group and for each jurisdiction are in the packet.