Flooding Risk Maps: Bay Area Flood Zones

The Bay Area faces several kinds of flood risk that are easy to miss on a sunny day. The bay shoreline is exposed to high tides and rising seas, and creeks and rivers overflow during intense winter storms. Hillside neighborhoods can face debris flows after heavy rain, and low-lying areas collect water from overwhelmed storm drains. Knowing where flood risk is highest, and what kind of flooding threatens each area, matters for residents, home buyers and anyone spending time outdoors in the storm season.

This winter, the most pressing risk is along the bay shoreline. El Niño has kept San Francisco Bay about a foot above the tide tables since early October, and the king tides arrive November 24-26 and December 23-25. The live check below shows how high the bay is running right now, and the official maps and gauges after it show what the water is doing around the region.

Official Live Flood Maps and Gauges

These free tools from federal, state and local agencies show what the water is doing now and what is forecast. Check them the evening before and the morning of a king tide or a big storm. Start with the live check of NOAA's San Francisco tide gauge, which compares the measured water with the tide tables.

The NOAA tide gauges and dashboard cover the bay shoreline, and the river and creek gauges cover flooding from rain.

What to Watch When King Tides and El Niño Raise the Bay

The 2026-27 king tides arrive November 24-26, December 23-25 and January 21-22. NOAA predicts the highest, 7.23 feet at the San Francisco gauge, for 10:37 AM on December 24. Those predictions assume the ocean is at its normal level, and this fall it is not. A Kelvin wave from El Niño, a slow, wide wave of warm water, has kept the bay about a foot above the tide tables since early October. In the first days of November, the gap was about 1.3 feet.

A few numbers at the San Francisco gauge put any tide forecast in context. All are in feet above mean lower low water, the baseline that tide tables use. The National Weather Service's minor coastal flood level there is about 7.0 feet. NOAA's own flood levels are 7.7 feet for minor flooding and 8.6 feet for moderate flooding. The record is 8.66 feet, set on January 27, 1983, when a winter storm hit during a strong El Niño. If the bay is still about a foot high, this winter's king tides would reach about 8 feet, above both minor flood levels.

Before a king tide morning, or any high tide during a storm:

• Add the gap to the tide. Check how far the measured water is running above the prediction, using the live check above or NOAA's gauge page, and add it to the predicted high tide.
• Check for a storm. Strong onshore winds, low air pressure and big waves can add another foot or more. If the National Weather Service issues a coastal flood advisory or warning, take it seriously even on a sunny morning.
• Adjust the time for your shoreline. Tides peak later in the South Bay and North Bay than at the Golden Gate, so check the high tide time at the NOAA station nearest you.
• Watch for rain on a high tide. Many storm drains and creeks empty into the bay. At high tide the water has nowhere to go, so moderate rain can flood streets that stay dry on a falling tide.
• Move cars and plan your route. Move cars out of shoreline lots before high tide, such as the Manzanita park-and-ride in Mill Valley. Expect water on low routes like Miller Avenue in Mill Valley, the Embarcadero sidewalk and bike lane near Pier 14, and the Bothin Marsh path between Mill Valley and Sausalito.
• Stay out of the water. Never drive or walk into water covering a road. Bay water is salty and can damage a car's brakes and electronics as well as strand it.

The Four Types of Bay Area Flooding

Bay Area flooding does not come from a single source. Four distinct flooding types affect different parts of the region, and understanding which type threatens a given area changes what to watch for and how to prepare.

The first is creek and river flooding, when storms deliver more rain than creeks, rivers and drains can carry. In February 2017, Anderson Reservoir filled and spilled, and Coyote Creek flooded the Rock Springs neighborhood of San Jose. About 14,000 people were ordered to evacuate. Anderson has been kept nearly empty since 2020 while its dam is rebuilt. Valley Water finished a first set of flood barriers along the creek in 2025 and plans more floodwalls through 2028. San Francisquito Creek, on the line between Palo Alto and East Palo Alto, the Petaluma River, the Napa River and the Russian River at Guerneville also flood in heavy winters. You can predict where these floods happen, if not when, because the same creek corridors flood again and again. The Great Flood of 1862, the worst in California's recorded history, was river flooding on a statewide scale.

The second is tidal and coastal flooding along the bay shoreline. Low areas built on bay fill, such as Foster City, Redwood Shores and parts of the East Bay waterfront, sit only a few feet above sea level. Alviso has a different problem. Groundwater pumping in the 1900s made the land there sink, and parts of it now sit below sea level behind levees. Tidal flooding comes during king tides and other very high tides, and it is worst when a storm adds surge, onshore wind and rain. This winter's El Niño high water makes it more likely, and sea level rise is making it more frequent and more severe.

The third is urban stormwater flooding, when overwhelmed storm drains back up onto streets and into low-lying properties. It is the most common everyday flooding in dense Bay Area communities during heavy rain. In San Francisco, the low ground around 17th and Folsom streets in the Mission and the Cayuga Avenue area near Interstate 280 are known trouble spots. Low-lying parts of Oakland and older neighborhoods with undersized drains are also exposed.

The fourth is debris flows and landslides on steep slopes, where soaked hillsides send mud, rock and water downhill. This is the most dangerous kind of flooding in the Bay Area. Debris flows can move fast and in unpredictable directions, and they can be powerful enough to destroy buildings. The Santa Cruz Mountains, steep Marin County hillsides and the Oakland hills have all had damaging landslides in recent wet winters. The risk of debris flows is highest on slopes burned in the past few years, because fire strips away the plants and roots that hold soil in place.

Bay Area Communities at Highest Flood Risk

FEMA flood maps mark Special Flood Hazard Areas, places with at least a 1% chance of flooding in any year, often called the 100-year flood zone. In the Bay Area, the highest-risk zones include Alviso, one of the lowest communities in the region, and parts of East Palo Alto near the bay and San Francisquito Creek. They also include low-lying parts of San Jose along Coyote Creek and the Guadalupe River, the Napa River corridor, the Petaluma River floodplain and the lower Russian River. Homes in these zones need flood insurance to get a federally backed mortgage.

FEMA's maps do not capture every kind of flood risk. They can miss street flooding where drains are too small, future flooding from sea level rise, and debris flows on steep, soaked slopes. That is why San Francisco publishes its own stormwater flood map, and why state and federal agencies publish separate maps for sea level rise and debris flows. The address maps further down this page cover those gaps.

Sea Level Rise and Bay Shoreline Flooding

Rising seas will turn today's king tide flooding into routine flooding. In 2020, the Adapting to Rising Tides program of the Bay Conservation and Development Commission (BCDC) studied the whole bay shoreline. It found that 4 feet of flooding above today's average high tide would affect nearly 13,000 existing homes and 104,000 jobs. Nearly 28,000 socially vulnerable residents near the shoreline would face regular flooding in their neighborhoods. That much water could come from sea level rise alone, or from a smaller rise combined with a storm.

California's 2024 sea level rise guidance projects 1.6 to 3.1 feet of rise at San Francisco by 2100, compared with 2000, under its Intermediate-Low and Intermediate scenarios. Its higher scenarios reach 4.8 to 6.5 feet. This fall's extra foot of El Niño water is about the rise the Intermediate scenario projects for San Francisco by around 2060, so the shoreline flooding seen now is a preview. Low-lying shoreline communities, including parts of San Mateo, Redwood Shores, Foster City, Alviso, Richmond and Oakland, are among the first to flood as the water rises.

The risk along the shoreline is greater because many of these communities were built on bay fill, land created by filling shallow parts of the bay with soil. Bay fill often sits barely above today's sea level. It also rests on soft sediment that can amplify shaking during earthquakes and slowly sinks over time.

How to Check the Flood Risk at an Address

The starting point for checking flood risk at a specific address is FEMA's Flood Map Service Center at msc.fema.gov. Enter your address to see the official FEMA flood zone designation. Zones A and AE are high-risk areas in the 100-year floodplain, and Zone VE is a coastal high hazard area where waves add to the flooding. Shaded Zone X marks moderate risk, inside the 500-year floodplain, and unshaded Zone X is lower risk.

FEMA's zone is only part of the picture, so check the other official maps below too. San Francisco requires sellers and landlords to disclose whether a property is in the SFPUC's 100-year storm flood risk zone.

The Bay Shoreline Flood Explorer also helps during king tides. A king tide with this fall's extra foot of water would reach about 2 feet above an average high tide at the San Francisco gauge. The explorer's 12-inch and 24-inch maps give a rough sense of which shoreline areas are lowest. For tsunami zones, the California Geological Survey publishes separate hazard maps for the coast and bay shoreline, as our guide to whether a tsunami can hit San Francisco explains.

What to Do When Flood Alerts Are Issued

The National Weather Service issues two sets of flood alerts in the Bay Area. For rain, a Flood Watch means flooding is possible, a Flood Advisory means minor flooding is expected, and a Flood Warning means flooding is happening or about to. A Flash Flood Warning means fast, dangerous flooding, often from rapid creek rises or debris flows on steep or burned slopes. A Flash Flood Emergency, which is rare, means a severe threat to life. For the shoreline, Coastal Flood Advisories, Watches and Warnings cover king tides, storm surge and high water from big waves.

When flood warnings are issued, avoid crossing any flooded road or creek, even if the water looks shallow. The National Weather Service says six inches of fast-moving water can knock over an adult, 12 inches of rushing water can carry away most cars, and 2 feet can carry away most SUVs and trucks. Do not drive through flooded underpasses, which can fill quickly and trap vehicles underwater. If you live in a known flood zone, move vehicles to higher ground before a storm and know the evacuation routes that avoid flood-prone areas.

Tidal flooding rises and falls with the tide, so it usually lasts a few hours around high tide rather than all day. Plan around the high tide time at the station nearest you, and give low shoreline roads time to drain afterward. Sign up for your county's alerts through CalAlerts.org to get evacuation orders by text.