About these numbers
This is a planning tool, not an official forecast, warning, or evacuation order. Follow local emergency officials.
Flood areas come from static, modeled maps. Bay water levels use NOAA's sea level rise maps, which show everywhere connected to the Bay below a given water level and can overstate flooding behind levees and shoreline protection. FEMA zones are the official regulatory maps. Neither predicts a specific storm.
People and homes in flooded areas come from 2020 Census blocks, assuming residents are spread evenly within each block. Other figures apply American Community Survey 2020–2024 tract estimates to the flooded share of each tract, assuming flooded residents resemble their tract overall. All figures are estimates, and small groups can have wide margins of error.
Critical facilities, shelter sites, and roads are shown where the flooded area covers their mapped point or line. Hospitals, care facilities, and dialysis clinics come from California licensing lists (CDPH, and CDSS Community Care Licensing as of May 2025). Fire stations, police stations, libraries, community centers, places of worship, and roads come from OpenStreetMap and are incomplete; schools come from the California Department of Education directory. Pre-identified shelters show their capacity; other sites show an estimated capacity, the typical capacity of pre-identified shelters of the same type, which can be off by a third or more. Pre-identified shelters are sites identified in advance as possible emergency shelters; whether a site opens depends on the emergency. Potential shelters are other sites that could plausibly serve as shelters and have not been checked or confirmed. Key shelters are the dry sites, up to three per city, with the most affected residents within the chosen distance (residents without a car count twice). Distances are measured along OpenStreetMap walking paths (1 km and 2 km, at about 4 km/h) or roads (5 km), not in a straight line, and any path or road the flood layers cover is treated as closed, though bridges and tunnels stay open. Residents of flooded homes are assumed able to reach a dry path within 500 m; if none is that close, they are counted as having no shelter in range. OpenStreetMap paths can be incomplete, and routes do not account for stairs, steep hills, or mobility needs. Site size compares each site's main building, from OpenStreetMap building outlines, with other sites of the same type; it is approximate and not a measured capacity. Bridges, elevated roadway, and tunnels are not counted as flooded roads.
Sources: NOAA Office for Coastal Management Sea Level Rise data; FEMA National Flood Hazard Layer; U.S. Census Bureau (2020 Census and ACS 5-year 2020–2024); California Department of Public Health; California Department of Social Services; California Department of Education; OpenStreetMap contributors. Basemap by OpenFreeMap, © OpenMapTiles, data from OpenStreetMap contributors.