Methodology
Philosophy
UnzipRisk presents historical disaster data — what happened, when, and how severe it was. We do not compute predictive risk scores or make forecasts. We show historical facts: event counts, damage totals, severity breakdowns, and trends. You draw your own conclusions.
Data Sources
| Source | Hazard Types | Coverage |
|---|---|---|
| NOAA Storm Events Database | Tornado, hail, wind, hurricane, blizzard, extreme cold, heat, and selected flood/storm records | 1950–present |
| USGS Earthquake Catalog | Earthquakes | 1950–present in the active dataset |
| USGS wildfire perimeter records | Wildfire perimeters & acres burned | Primarily 1900–present; some source records contain older or approximate historical years |
ZIP Code Attribution Algorithm
Each disaster event is attributed to one or more ZIP codes based on its geographic footprint:
- Point events (exact coordinates known): Assigned to the ZIP containing that point, plus nearby ZIPs within a category-specific radius.
- Area events (polygon/track): All ZIPs whose boundaries intersect the event polygon are included.
- County-level or low-precision events (when a source lacks precise event geometry): Attributed using county/ZCTA spatial matching or county-centroid distance, and treated as approximate.
Attribution radii vary by hazard type — tornado events use a smaller radius than hurricane events, reflecting their different geographic footprints. Events attributed from nearby areas are marked with their distance from the ZIP centroid.
Severity Normalization
All events are normalized to a 1–5 severity scale for consistent comparison across hazard types:
| Category | Sev 1 | Sev 2 | Sev 3 | Sev 4 | Sev 5 |
|---|---|---|---|---|---|
| Tornado | EF0 | EF1 | EF2 | EF3 | EF4-5 |
| Hurricane | — | Cat 1 | Cat 2-3 | Cat 4 | Cat 5 |
| Earthquake | <3.0 | 3-4 | 4-5 | 5-6 | 6+ |
| Flood | Minor | Moderate | Major | Severe | Catastrophic |
| Wildfire | <100ac | 100-1K ac | 1K-10K ac | 10K-50K ac | 50K+ ac |
| Hail | <1" | 1-2" | 2-3" | 3-4" | 4"+ |
Time Windows
Data can be filtered by time window: 1 year, 5 years, 10 years, 20 years, and all-time. The default ZIP-page view shows the last 20 years. The "all-time" window includes source records back to 1950 for NOAA storms and USGS earthquakes, plus USGS wildfire records that may include older or approximate historical years.
Limitations
- Approximately 5,000 PO-box-only ZIPs have no geographic area and are excluded.
- County-level events are attributed to all ZIPs in the county — this may overcount for very large counties.
- Historical data before 1990 is less complete, especially for smaller events.
- Damage figures are nominal (not inflation-adjusted).
- Data is refreshed periodically as federal agencies publish updates.
Geographic Boundaries
ZIP code boundaries are based on ZIP Code Tabulation Areas (ZCTAs) as defined by the U.S. Census Bureau. ZCTA boundaries don't perfectly align with USPS ZIP codes — this is a known limitation of all ZIP-level geographic analysis.