Across parts of Massachusetts, flood exposure shows up in the same ZIP codes as one of two other measurements. Here is exactly what each of the three measurements is, what kind of instrument produced it, and what reference level it does — and does not — have.
Flood exposureFEMA flood mapMapped · not modeled
This is how much of a ZIP code's land sits inside the 1% annual-chance floodplain — the area FEMA maps as the Special Flood Hazard Area, often nicknamed the "100-year floodplain." Despite that nickname it does not mean one flood per century: the 1% chance applies every single year, so such floods can strike in back-to-back years. It is read off FEMA's published flood maps rather than modeled, and it describes land, not any particular home.
FEMA National Flood Hazard Layer — the Special Flood Hazard Area (1% annual chance). A federal flood-map designation of land; it is not a health limit, and no ZIP on this page is described as having crossed a safety line.
Households with no vehicleCensus survey estimateACS · ZCTA-native
This is the share of households in a ZIP code with no vehicle available, from the Census Bureau's American Community Survey. It counts households rather than people, it is an estimate drawn from a sample rather than a full census, and it says nothing about why a household has no car. Next to flood exposure it is a logistical fact and nothing more: an evacuation that assumes a car is harder without one.
US Census Bureau, American Community Survey — a survey estimate carrying sampling error. There is no federal reference level for this measure, and none is implied.
Humid-heat daysModeled heat stressOccupational reference — not federal
This is the average number of days a year when the daily-high wet-bulb globe temperature reaches 28 °C — a heat-stress measure that combines temperature, humidity, sun and wind. Humidity matters because it slows the body's main way of cooling itself, sweat evaporating from the skin, so the same air temperature is harder on the body when the air is humid. The count is modeled across a 2011–2020 climatology, not measured at your address.
Cornell wet-bulb globe temperature data. The 28 °C line comes from NIOSH/ACGIH occupational heat-stress guidance written for workplaces — it is not a federal environmental limit, and reaching it is not a regulatory exceedance.
What this is — and isn't. These are separate exposures recorded for the same place. This page does not claim one causes another, does not combine them into a single risk number, does not rank areas by how pronounced an overlap is, and does not connect any of them to a health outcome. It reports where two figures are elevated together, and nothing more.