in 100-yr flood zones
newly revealed by AI
(+69% vs FEMA alone)
inadequately mapped
Every 100-year flood zone FEMA has ever published, against every zone the model generated — the entire contiguous United States at 30-meter resolution. Drag the divider to compare. Amber is FEMA; cyan is the AI.
1 — Terrain
The only nationwide input is elevation: the USGS 3DEP digital elevation model at 30-meter resolution, rendered with hillshades and color gradients so the terrain's structure — valleys, fans, floodplains — is visually explicit.
2 — Tiling
Terrain and FEMA's existing flood maps are cut into ~300,000 aligned square tiles on the standard web-map grid, at multiple scales. Every place FEMA has ever mapped becomes a training example: this terrain produced this flood map.
3 — The model
A conditional GAN — the image-translation architecture behind pix2pixHD — learns to draw flood zones from terrain alone. Three discriminators judge its output at three zoom levels; training ends when they can no longer tell generated flood maps from FEMA's.
4 — Judged against reality
Where FEMA maps exist, the model's output can be scored directly. Out of sample, the national model reaches 0.81 pixel precision in Texas and New Jersey — and unlike locally trained models, it holds up in terrain it has never seen.
5 — The whole country
The trained model then runs over all of CONUS — including the two-thirds of river miles FEMA never modeled. The tiles are stitched and vectorized into a single continuous flood layer, in the same format as the NFHL itself.
Laying the AI layer over the NFHL nearly doubles the exposure count. These are people and buildings inside 100-year flood zones that no regulatory map currently shows.
Validation
Against held-out FEMA maps in three geomorphologically distinct states, the single national model trades a little in-sample precision for markedly better generalization:
| Region | Local model, in-sample | National model, out-of-sample | mIoU gain | ||||
|---|---|---|---|---|---|---|---|
| Prec | Rec | mIoU | Prec | Rec | mIoU | vs local | |
- These maps show fluvial and coastal 100-year flood extents. They largely exclude pluvial (rainfall-driven) flooding, because the FEMA maps the model learned from exclude it.
- They are a research product, not a replacement for regulatory FEMA flood zones. For insurance, lending, or permitting decisions, consult the FEMA Map Service Center.
- Out-of-sample accuracy varies by terrain (mIoU 0.48–0.54 across validation states); treat any single location as an indication, not a determination.