Methodology · component
Climate / Disaster Risk — how we measure it
One component of the ZipVitals Score. This page covers only this component — what it is built from, how those sources reach your ZIP, where they stop, and how it enters the composite. For the full recipe and the whole weight table, see the main methodology page.
Effective weight 0.0526 of the composite · higher = worse
Where this sits in the Score
The two climate exposures we can measure honestly at ZIP level: dangerous heat, and mapped flood hazard. Deliberately narrower than the domain name suggests — and we say so rather than scoring perils we cannot reach.
Feeds domain
Climate / Disaster Risk
0.0526
effective weight · nominal 0.05 · higher = worse
Climate / Disaster Risk is 1 of 9 scoring domains. Life expectancy is held out of the composite as an independent validator, so the nine renormalize to sum to 1.00 and this domain’s share lands at 0.0526.
It is built from 3 sources, listed below with what each one contributes and what it cannot tell you.
The sources feeding Climate / Disaster Risk
Each source is labeled with what kind of number it is — observed, model-based, or administrative — because a modeled risk surface and a counted facility are not the same kind of fact. We name which is which.
Cornell humid-heat exposure (WBGT)
Model-basedCornell University (published research dataset)
The average number of days a year of dangerous humid heat — days whose peak wet-bulb globe temperature reaches the recognized occupational danger band, averaged over a ten-year window.
The honest limit: A ten-year average, not this year’s weather. Continental US only: Alaska, Hawaii and the territories are left unavailable rather than estimated.
CDC EPHT extreme-heat days
Model-basedCDC Environmental Public Health Tracking
The average number of days a year at or above 95 °F — the dry-heat pathway, complementary to humid heat.
The honest limit: Continental US only, on the same terms as the humid-heat measure. A year absent from the source is treated as missing, never as a year with zero hot days.
FEMA National Flood Hazard Layer
AdministrativeFederal Emergency Management Agency
The share of the ZIP's land area that sits inside a FEMA-designated flood zone.
The honest limit: A regulatory map boundary — the line insurance and building rules are drawn from — not a forecast that those areas will flood and not a determination about any individual property. It is area, not population, so it does not tell you what share of residents live in the zone. Where FEMA has not mapped a ZIP we publish nothing, which must never be read as "no flood risk."
How these reach your ZIP
Every value is a fact about the ZIP itself. A source that is not published at ZIP level is rolled up against a published Census boundary file, weighted by population or land area as appropriate — never inherited from the county or state and rebranded as the ZIP’s. Where a legitimate ZIP value cannot be produced, the metric is shown as unavailable.
- Cornell humid-heat exposure (WBGT)
- Census tract → ZIP, population-weighted.
- CDC EPHT extreme-heat days
- Census tract → ZIP, population-weighted.
- FEMA National Flood Hazard Layer
- An exact overlay of FEMA's flood-hazard polygons on the ZIP boundary.
Coverage & limitations — for this component
This is the honest part. Every limit below is a published, named limit of this component specifically, so you can judge how far to trust one of its numbers. We treat limitations as a trust signal, not fine print.
What these numbers actually are
- Flood-zone share
- The share of the ZIP's land AREA inside a FEMA-designated flood zone. That is a regulatory map boundary — the line insurance and building rules are drawn from — not a forecast that those areas will flood and not a determination about any individual property. It is area, not population: it does not tell you what share of residents live in the zone. Resolution: An exact overlay of FEMA's flood-hazard polygons on the ZIP boundary. Where FEMA has not mapped a ZIP, we publish nothing (see the coverage table above).
Where this component’s data stops
- Flood-zone share (NFHL)
- ~16.5% of ZCTAs sit on unmapped flood panels and carry no value. coverage-incomplete Framed as "not mapped," never as "no flood risk."
How it enters the Score
Every metric in this component goes through the same pipeline as the rest of the Score, then contributes to the Climate / Disaster Risk sub-score — which contributes its 0.0526 to the composite.
- Standardize. Each metric becomes a z-score against the national distribution of ZIP codes, so a concentration, a rate and a distance become comparable.
- Cap outliers. Each z-score is capped, so one extreme ZIP cannot dominate the scale.
- Build the sub-score. The capped metrics combine into the Climate / Disaster Risk sub-score, weighted by source and then equally within a source — so a source that publishes many metrics cannot swamp one that publishes few.
- Weight into the composite. Climate / Disaster Risk contributes 0.0526 to the domain-weighted sum, which is rescaled to the 0–100 Score.
Go deeper
This is one component of the method. Follow any of these for the whole picture, or for this component in context.