About the Northern Virginia Climate Resilience Atlas

Why this exists

Northern Virginia's jurisdictions plan for floods, heat, and storms with data scattered across a dozen federal portals. This atlas puts the region's hazard, vulnerability, and demographic record on one map, so a planner, an emergency manager, or a resident can answer a concrete question in minutes: where does water go, who gets hottest, what has storm damage cost, and who has the least capacity to cope.

Click any census tract and the atlas returns one combined readout: social vulnerability, the demographic flags that matter in an emergency, and the tract's hazard exposure. That cross-layer view, not any single dataset, is the point.

What each layer is for

Flooding

FEMA flood zones. Check any parcel or corridor against the regulatory floodplain before you zone it, buy it, or build on it.

Sea level rise scenarios. See which shoreline blocks stop draining as the tidal Potomac rises, and set setbacks and outfall designs before the water arrives.

Projected inland flood exposure. Compare how often each tract will see two-inch rain days by mid-century, and size culverts and detention where the increase is steepest.

Extreme heat

Observed urban heat. Find the Arlington blocks that ran hottest on a July afternoon, and target tree canopy and cooling centers block by block.

Projected extreme heat days. Overlay projected days at or above 95 °F on the SVI to find neighborhoods that are both hot and vulnerable, and put cooling investment there first.

Impervious surface. Spot the tracts where pavement drives both heat and runoff, and write redevelopment standards that pay down both risks at once.

Severe weather

Historical storm events. Filter 77 years of tornado, hail, wind, and flood reports by type and decade to brief responders on what actually hits each corridor.

Storm damage intensity. Rank jurisdictions by inflation-adjusted storm losses to argue mitigation budgets with evidence instead of anecdotes.

People and vulnerability

Social Vulnerability Index. Layer any hazard over the SVI to see who has the least capacity to prepare and recover, then aim outreach there first.

Demographic exposure. Switch the lens to seniors, young children, poverty, or car-free households, and plan evacuation and shelter capacity around the people who actually live there.

Data sources and credits

Every layer comes from a federal public-domain source or an attribution-only open source, snapshotted into this atlas's own files. Nothing here hot-links a government server at view time.

Dataset	Publisher	Used for	License / credit
National Flood Hazard Layer (snapshot)	FEMA	Flood zone layer, tract SFHA shares	U.S. Government work. Credit: FEMA. Loudoun County polygons come from the county's published regulatory floodplain service (major/minor floodplain), used because FEMA's export service would not deliver Loudoun; credit Loudoun County GIS.
Sea Level Rise viewer vectors, VA Northern region	NOAA Office for Coastal Management, Digital Coast	+1/+2/+3 ft inundation scenarios	U.S. Government work. Credit: NOAA OCM.
CMRA Screening Data (tract summaries)	Interagency (resilience.climate.gov / USGCRP)	Projected heat days, 2-inch rain days	U.S. Government work. Credit: CMRA.
Urban Heat Watch, Arlington VA, July 15 2021	NOAA NIHHIS + CAPA Strategies (VFIC cohort)	Observed heat traverse points	Public campaign data. Credit: NIHHIS / CAPA Strategies. Arlington is the NoVA locality with a campaign; Fairfax and Alexandria have none to date.
Storm Events Database, 1950–2026	NOAA NCEI	Event points, damage choropleth, loss model	U.S. Government work. Credit: NOAA NCEI.
Social Vulnerability Index 2022	CDC / ATSDR	SVI layer, readout, equity weighting	Public domain. Credit: CDC/ATSDR.
TIGER/Line cartographic boundaries 2024	U.S. Census Bureau	Tracts, county, place outlines	Public domain. Credit: U.S. Census Bureau.
ACS 5-year estimates 2018–2022	U.S. Census Bureau	Demographic layer, exposure model	Public domain. Credit: U.S. Census Bureau.
NLCD 2021 impervious surface	USGS / MRLC	Impervious layer	Public domain. Credit: USGS/MRLC.
GlobalMLBuildingFootprints (2026-07-24 release)	Microsoft (Bing Maps)	Building footprints layer, 2D and 3D views, ML height estimates	CDLA Permissive 2.0. Credit: Microsoft GlobalMLBuildingFootprints. Heights are model estimates from imagery, not survey data.
Protomaps basemap (build 2026-07-23)	Protomaps, from OpenStreetMap	Basemap ("Streets")	Open style; data ODbL. © OpenStreetMap contributors.
World Imagery tile service (view-time)	Esri	Optional "Satellite" basemap	Tiles © Esri — Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community. Streamed at view time, not snapshotted; the only layer that needs the network.
CPI-U (CPIAUCSL)	U.S. BLS via FRED	Inflation adjustment of storm damages	Public data. Credit: BLS / FRED.

Excluded by license: Virginia's statewide Fathom flood model (state sublicense only), First Street / Risk Factor (proprietary), Esri-hosted basemaps, and Google Maps data.

Methodology & assumptions (mitigation analytics)

The analytics panel and the companion workbook (analytics/loss_model.xlsx) price mitigation with public, citable methods. Every number they show is illustrative, built for ranking places and hazards, not for appraising a specific project.

Annualized loss. NCEI Storm Events damages (property plus crops), each year converted to current dollars with annual-average CPI-U (FRED CPIAUCSL), divided by the 77-year record.
Discount rate: 7%. The OMB Circular A-94 (1992) rate, which FEMA reinstated for Hazard Mitigation Assistance benefit-cost analysis effective April 8, 2025. The workbook exposes it as an input.
Project life: 30 years, a common FEMA BCA default for building projects. Also an input.
Benefit-cost ratios. NIBS, Natural Hazard Mitigation Saves (2019 report, Table 1, federal-grants row): riverine flood 7:1, wind 5:1, earthquake 3:1, wildland-urban fire 3:1, 6:1 across all hazards. The 2019 study remains the institute's latest full report as of this build (July 2026). No headline ratio is hardcoded from memory; the workbook reads these values from a labeled table with the citation attached.
Exposure. Property exposure multiplies each tract's housing units by its median home value by its share inside the special flood hazard area. Vulnerable population counts residents of tracts at or above the 75th SVI percentile that also touch the SFHA or fall in the top quartile of projected heat days.

Storm Events undercounts small losses and geocodes damage to the reporting jurisdiction, so treat jurisdiction totals as floors. Commission a project-level FEMA BCA before committing funds.

Geographic scope

The beta covers the Northern Virginia Regional Commission core: Arlington, Fairfax, Loudoun, and Prince William counties, the cities of Alexandria, Fairfax, Falls Church, Manassas, and Manassas Park, and the incorporated towns within those counties. The pipeline clips to a single list of FIPS codes in config.py; edit that list and re-run to cover more of Virginia.