Risk-assessment baseline packet. County FIPS 26161. Release 2026-10, data as of 2026-09-30.
Summary
Plan status as of 2026-09-30: Expired on 2010-07-12. Plan: Washtenaw County (FEMA plan 101029), approved 2005-07-13.
Since the plan was approved on 2005-07-13: 2 new hazard declarations (2 incidents) and 515 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 ($46,633,134 a year), Tornado ($20,847,641) and Cold Wave ($10,696,760).
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
14 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, Tornado and Cold Wave.
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: 3 in hail, 2000-05-09
- Thunderstorm Wind: 80 kt (92 mph), measurement type not recorded, Thunderstorm Wind, 1990-01-25
- Tornado: F3 tornado, 1953-06-08, 11.3 mi path length (whole path, pre-1996), 70 yd wide, $25,000 property; crops not recorded (1953 dollars), 1 direct death, 5 direct injuries
Supports FEMA checklist item B1-d Previous occurrences
Federal declarations for this area: 12 declarations covering 8 separate hazard incidents counted in this packet; each with type, dates and county Public Assistance dollars.
New since the last plan (approved 2005-07-13): DR-4925-MI, DR-4607-MI, DR-4494-MI, EM-3455-MI and EM-3225-MI.
3 statewide declarations listed separately.
Hazards with no Storm Events record and no federal declaration are stated as such (8 of 18).
Storm Events history: 986 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, Heat Wave, Ice Storm, Inland Flooding, Landslide and Tornado
- Possible: Drought
- Unlikely: Hurricane
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 (107 tracts; rated tracts only).
30 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 jurisdictions in this plan (for example 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 2005-07-13: $23,221,500 in county-coded records (428 records); $57,812,500 reported for the zone (87 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 372,064; building value $89,377,883,384 and agriculture value $117,380,975 (total, not at risk).
National Risk Index rating Relatively Moderate; 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): 1 repetitive loss, 1 severe repetitive loss. NFIP insurance definition: 10 and 1.
Mitigated 0; insured 5; NFIP data as of 2026-08-02. Counts by occupancy group and for each jurisdiction are in the packet.