About these numbers
This is a planning tool, not an official forecast, warning, or evacuation order. Follow local emergency officials.
Flooding uses NOAA's 3 m lidar elevation model and its high-tide surface: a spot floods when Bay water at the chosen level can reach it over ground lower than the water ("bathtub" method). It does not model pumps, drainage, waves, or how long water stays high. Results match NOAA's published flood maps at +2.0, +2.5, and +3.0 ft. Tide gates, culverts, and narrow walls or levees may be missing or understated in the elevation data.
"If embankment holds" blocks the low points where water first gets over the shoreline protection along the San Leandro Bay channel at Harbor Bay, as if that stretch were higher than the elevation data shows.
A road is impassable where water on it would be more than 6 inches deep; bridges and tunnels stay open. An area is cut off by car when its roads no longer connect to the rest of the county. For walking, a path is closed wherever any water covers it, so an area can be cut off on foot before it is cut off by car. Residents come from the 2020 Census (by block); flooded residents assume people are spread evenly within each block.
Shelter distances follow OpenStreetMap paths (on foot, at about 4 km/h) or roads (by car), not straight lines, with flooded paths closed and bridges and tunnels left open. Residents of flooded homes are assumed able to reach a dry path within 500 m. OpenStreetMap paths can be incomplete, and routes do not account for stairs, steep hills, or mobility needs.
The ART layer is the Bay Conservation and Development Commission's Adapting to Rising Tides regional flood map (CC-BY), shown at its nearest available level (24 or 36 inches). Shelter capacities and estimates are as on the main map.
Sources: NOAA Office for Coastal Management (elevation model, tidal surface, sea level rise maps); BCDC Adapting to Rising Tides; U.S. Census Bureau; California Department of Public Health; California Department of Social Services; California Department of Education; OpenStreetMap contributors.