Risk-assessment baseline packet. County FIPS 46109. Release 2026-10, data as of 2026-09-30.
Summary
Plan status as of 2026-09-30: Approved, expires 2030-07-02. Plan: Roberts County, SD Hazard Mitigation Plan 2025 (FEMA plan 110416), approved 2025-07-03.
Since the plan was approved on 2025-07-03: no new hazard declaration and 40 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): Inland Flooding ($3,301,270 a year), Cold Wave ($2,670,929) and Tornado ($919,522).
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): Inland Flooding, Cold Wave 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 10 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 in hail, 1997-07-19
- Thunderstorm Wind: 83 kt (96 mph) measured gust, Thunderstorm Wind, 2020-06-04
- Tornado: F2 tornado, 1951-07-08, 33 yd wide, damage not recorded (pre-1996 record), 1 direct injury
Supports FEMA checklist item B1-d Previous occurrences
Federal declarations for this area: 24 declarations covering 21 separate hazard incidents counted in this packet; each with type, dates and county Public Assistance dollars.
New since the last plan (approved 2025-07-03): none.
3 statewide declarations listed separately.
Hazards with no Storm Events record and no federal declaration are stated as such (9 of 18).
Storm Events history: 683 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, Strong Wind and Winter Weather
- Likely: Cold Wave, Drought, Heat Wave, Ice Storm, Inland Flooding, Landslide and Tornado
- Unlikely: Earthquake and Wildfire
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 (4 tracts; rated tracts only).
10 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 offices and boards filed under their own names, such as a sheriff's office or a conservation board, 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 2025-07-03: $0 in county-coded records (16 records); $0 reported for the zone (24 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 10,217; building value $2,895,850,619 and agriculture value $263,245,283 (total, not at risk).
National Risk Index rating Very Low; social vulnerability Relatively High; community resilience Relatively Low.
Supports FEMA checklist item B2-c Repetitive loss properties
Repetitive-loss properties, FMA definition (44 CFR 77.2): 1 repetitive loss, 0 severe repetitive loss. NFIP insurance definition: 5 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.