Choose a town to begin
Results show the change from today's flood exposure.
Tax revenue at risk over time
Added annual property tax revenue at risk relative to today, for each NOAA 2022 scenario. The red line is the selected scenario.
Parcel exposure map
Run an analysis to map exposure.
Shading shows modeled flood extent and depth on 1 m lidar ground for the selected scenario and year; parcel colors use the same classes, judged at each parcel's buildings.
Where the loss comes from
Selected scenario and year.
By land use
Flooded area over time
Acres of parcel land below future high tide or inside the 1% flood, by decade, for the selected scenario. The dashed box is the selected year.
Run an analysis to see flooded area over time.
Parcel ledger
Exposed parcels in the selected scenario and year. Select a column heading to sort, or a row to find the parcel on the map. Dollar values are in today's dollars.
| Parcel ID | Location | Use | Assessed | Ground (ft) | Hazard | Depth (ft) | Lost to tide | 1% flood damage | Added tax / yr |
|---|---|---|---|---|---|---|---|---|---|
| No town analyzed yet. | |||||||||
Method and sources
Parcels and values. Parcel boundaries with assessed and appraised land and building values come live from the Connecticut CAMA and Parcel Layer. Connecticut assesses property at 70% of appraised value.
Ground elevation. Each parcel is sampled at a point inside its boundary (five points in finer mode) against the USGS 3DEP lidar elevation service, in feet NAVD88. Elevations for each town's parcels are saved ahead of time and refreshed quarterly; only points missing from the saved set are requested live. Only parcels in or near a FEMA flood zone, or within reach of the coast, are sampled.
Sea level rise. NOAA 2022 Interagency relative sea level scenarios load for the nearer of the Bridgeport and New London gauges, relative to 2005. Mean higher high water is interpolated between those gauges. Land below future high tide counts as permanently lost only if it is dry today.
Coastal flooding. Parcels in FEMA VE or coastal AE zones use their base flood elevation; other parcels within reach of a VE zone use the town's coastal still-water elevation. Both rise one-for-one with sea level after 2020. This bathtub approach ignores wave attenuation and flood protection.
Inland flooding. Parcels in riverine A, AE, AO and AH zones from the FEMA National Flood Hazard Layer use the base flood elevation (or zone depth) plus a rise in flood elevation that grows with the scenario. Parcels in the 0.2% annual chance zone begin to flood once that rise exceeds their assumed margin.
Buildings. Each building in the CT 2D Building Footprints layer is placed on the parcel that contains it, and its ground elevation is sampled at the footprint. Flood depth and tidal loss for buildings use each building's own ground, with the parcel's building value split by footprint area. Land loss uses the parcel's ground points. Parcels with no mapped building fall back to the parcel point.
Flood extent and depth. The map shading and the flooded-area chart compare USGS lidar ground elevation with the same water levels used for parcels: future high tide, the coastal 1% still-water elevation or the FEMA base flood elevation, each raised for the scenario and year. This bathtub method does not model flood barriers, drainage or wave effects.
From depth to dollars. Building damage follows the USACE generic depth–damage curve for one-story homes without basements, applied to depth above the first floor. Tax at risk adds assessed value lost to permanent inundation, a market discount on newly exposed parcels, and the annualized reassessment after a design flood. All dollar figures are in today's dollars: assessments and the mill rate stay at current values, with no inflation or appreciation, so the cumulative figure uses a real discount rate.
Use with care. This is a screening tool. A point inside each parcel stands in for the building location, elevations are bare-earth, and the assumptions panel holds values to replace with local figures. Connecticut's planning standard is 0.5 m (20 in) of sea level rise by 2050 (CGS 25-68o).