Check flood insurance requirements

The different areas of flood risk on the FIRM are represented by zone designations. These zone designations are used for flood insurance rating purposes. The zones are defined as follows:

Areas with high flood risk (Special Flood Hazard Areas)

• Zone AE – this zone, a SFHA shown in blue on the FIRM, is the area that is subject to flooding during the 1-percent-annual chance flood. For San Francisco, Zone AE areas are associated with the Bay and Pacific Ocean shorelines. These Zone AE areas may be affected by waves up to 3 feet in height.
• Zone VE – this SHFA, also shown in blue, is subject to flooding during the 1-percent-annual chance flood but is also affected by waves that are greater than 3 feet in height. FEMA refers to these zones as “coastal high hazard areas” due to the additional risk posed by such waves.
• Zone AO – this SFHA, also shown in blue, is subject to flooding that is 1 to 3 feet deep.

Areas of undetermined flood risk

• Zone D – this is an area of possible, but undefined, flood hazard. In San Francisco, this zone is used exclusively for the waterfront piers operated by the Port of San Francisco. Zone D areas are shown in yellow on the FIRM.

Areas of low or minimal flood risk

• Zone X (“shaded”) – these areas, shown in brown on the FIRM, are subject to flooding during the 0.2-percent-annual-chance (“500-year”) flood, or are expected to experience flooding less than 1 foot during the 1-percent annual event. This flood is less likely, but more severe, than the 1-percent-annual-chance flood.
• Zone X (“unshaded”) – these areas are shown without color on the FIRM. This zone is used for all other areas, including areas of minimal flood risk as well as areas that FEMA did not study or map. For San Francisco, FEMA did not study or map areas where street flooding occurs during heavy rains; these areas are shown in Zone X.

100-year flood or base flood

The FIRM shows areas that are at risk of flooding due to a flood that has a 1-percent chance of occurring in any year (also called the “100-year flood” and “base flood”). These areas are referred to as Special Flood Hazard Areas (SFHAs), and they are the primary feature for flood insurance and floodplain management purposes.

“100-year” floods do not occur only once in a hundred years. Such a flood can occur in any year. A 100‐year flood or storm event is less likely to happen than a typical storm, but they can and do happen sometimes within just a few years of each other or even within the same year.

500-year flood

The FIRM also shows areas at risk from a less likely but more severe flood (the 0.2-percent annual-chance or “500-year” flood), as well as areas that are at a lesser risk of flooding. The different areas of flood risk have “zone” designations. These zone designations are used for flood insurance rating purposes. See the response to question B.4 below for definitions of these zones.

For SFHAs, the FIRM shows Base Flood Elevations (BFEs), which are represented numerically on the map. The BFE is the expected level of the flood during the occurrence of the 1-percent annual-chance flood (that is, the 100-year flood or base flood). The BFE is used for flood insurance rating and floodplain management purposes.

Base Flood Elevation (BFE)

The BFE is the level of the flood during the occurrence of the 1-percent-annual-chance flood (that is, the “100-year flood” or “base flood”). This elevation is tied to a datum that is roughly equivalent to sea level. For example, if the FIRM shows a BFE of 10 feet at a given location, this means that the surface of the flood at that location reaches a level of 10 feet above the datum (approximately sea level); it does not mean that the flood is 10 feet deep there. There are some SFHAs, designated Zone AO, that represent more shallow flooding. These zones are accompanied by a number (1, 2, or 3) that represents the average depth of flooding in feet above the ground surface at these locations.

SFPUC’s 100-Year Storm Flood Risk Map

The SFPUC 100‐Year Storm Flood Risk Map shows flood risk from storm runoff only. It does not consider flood risk in San Francisco from other causes, such as inundation from the San Francisco Bay nor Pacific Ocean, which are shown on the FIRM that FEMA has prepared for San Francisco.

The FIRM does not show flooding from storm runoff in San Francisco, because our historical creeks and other inland waterbodies have been built over and are no longer open waterways. In most areas, the flood hazards identified by SFPUC and FEMA are separate. There are a few areas near the shoreline of San Francisco where SFPUC’s Flood Risk Zones overlap with the FEMA‐designated floodplains.

Learn more about the 100-Year Storm Flood Risk Map

Areas affected by sea-level rise

FEMA has prepared the FIRM using data for current conditions. FEMA’s analyses do not consider what may happen in the future due to sea-level rise. The SFHAs shown on the FIRM are generally in the areas that may be flooded under future sea-level rise conditions. However, there are areas outside of the SFHAs that may also be at risk of flooding in the future. The City is addressing these areas through other planning and regulatory mechanisms.

For information on flood risk from sea level rise, see the Sea Level Rise data viewer.