Casa de Tableta · Photo: W Nowicki · CC BY 3.0FEMA puts Portola Valley’s expected hazard damage per building above that of 95% of U.S. towns, mostly from earthquakes
On FEMA’s National Risk Index, Portola Valley gets a D for hazard risk: higher expected damage per building than 95% of U.S. towns, #536 of 847 in California. Most of that expected damage is earthquakes (64%), then river and rain flooding (26%). Flood insurance has paid 12 claims here since 1979.
Graded on FEMA’s expected yearly building damage per dollar of building value (NRI v1.20, December 2025), weighted by where residents live; flood claims are shown, not graded. How hazard risk is graded
What Portola Valley faces
Each hazard’s share of the building damage FEMA expects here, and how its rate compares with the rest of the country.
Earthquakes
River and rain flooding
Wildfire
Shares are of FEMA’s expected building damage, the measure the grade uses; ranks compare each hazard’s building-damage rate with all 85,154 U.S. census tracts. In FEMA’s terms, river and rain flooding is FEMA’s “Inland Flooding” (rivers and streams overflowing their banks, or rain overwhelming drainage). FEMA defines coastal flooding as high or rising tides and storm surge, so surge damage is counted there. Drought isn’t listed: FEMA counts its losses in crops only.
What’s behind Portola Valley’s grade
Earthquakes are 64% of the building damage FEMA expects in Portola Valley, and Portola Valley’s rate of earthquakes damage is in the top 2% of U.S. census tracts. Wildfire adds 6%, at a rate in the top 4% of U.S. census tracts.
D #536 of 847 in California; higher expected damage per building than 95% of U.S. towns (21,298).
All of Portola Valley’s residents live in one census tract; the figures are that tract’s.
The typical California town has higher expected damage than 92% of U.S. towns; within the state, Portola Valley has more expected damage per building than 63% of California towns.
In dollars, FEMA expects about $7.1M a year in losses across Portola Valley: $6.0M to buildings, the rest to people and crops.
Does Portola Valley flood? Sometimes: 12 flood claims since 1979
Every paid claim on a federal flood insurance policy in Portola Valley, from FEMA’s records: 6.3 per 1,000 homes, more than 65% of the 13,809 U.S. towns with a flood insurance record.
- The Pineapple Express - Southern5 claims · $484K
- The California Atmospheric River1 claim · $25K
Portola Valley isn’t in FEMA’s Community Rating System, which cuts flood insurance up to 45% in towns that do extra flood-proofing.
Insurance rates: San Mateo County.4 federal disasters brought FEMA money to Portola Valley
Disasters that paid out in Portola Valley itself (aid to households or repair grants to the Town of Portola Valley), newest first, with that year’s flood claims.
- 2022Severe Winter Storms, Flooding, Landslides, and Mudslides16 households applied for aid$111K aid approved$112K to the Town of Portola Valley for repairs1 flood claim paid that year
- 2020Wildfires20 households applied for aid$19K aid approved
- 2017Severe Winter Storms, Flooding, and Mudslides$25K to the Town of Portola Valley for repairs
- 2005Severe Storms, Flooding, Mudslides, and Landslides$29K to the Town of Portola Valley for repairs1 flood claim paid that year
San Mateo County has had 19 natural disasters declared by the President since 1953, most often severe storms, then floods. Not counted: the 2005 Hurricane Katrina evacuee emergency, which covered counties that took in evacuees.
Also 2 FEMA wildfire suppression grants (Fire Management Assistance, not a disaster declaration) for fires in San Mateo County, 2010–2020.
Old photos of Portola Valley after a storm or flood belong in the town’s history. Add one, or share what you remember below.
Add to the Portola Valley archive →Portola Valley and its neighbors
Portola Valley is 3rd of the 4 graded towns here, from least expected damage per building to most. Tap a town to see its hazards.
Hazard risk = FEMA’s expected yearly building damage per dollar of building value, vs. the 21,298 U.S. towns we grade; the map is shaded by fifths of the same scale. Flood claims = paid federal flood insurance claims on record.
Get ready for what Portola Valley faces
A short kit for the hazards that drive the building damage here, what to check before you buy, and where neighbors get alerts.
- Drop, cover and hold on.
- Strap tall furniture and the water heater to the wall.
- Know how to shut off the gas.
- Turn around at flooded roads: a foot of moving water can carry off a car.
- Flood insurance usually takes 30 days to start, so buy it before the forecast.
- Keep papers and medicines up high, in a grab-and-go bag.
- Clear dead leaves and brush within 5 feet of the house.
- Sign up for local alerts and know two ways out.
- Keep N95 masks for smoky days.
- Look up the address on FEMA’s flood map.
- Ask the seller or landlord whether it has ever flooded, and what flood insurance costs there.
- Get a flood insurance quote early: policies usually start 30 days after you buy.
Know where neighbors sign up for alerts? Add it to the Handbook so everyone has it.
Questions about natural hazards in Portola Valley
Is Portola Valley at risk for natural disasters?
On FEMA’s National Risk Index, Portola Valley has higher expected damage per building than 95% of U.S. towns: D for hazard risk, #536 of 847 in California. Most of the expected damage is earthquakes (64%) and river and rain flooding (26%). The figures are for the one census tract the town shares with its neighbors. This is FEMA’s model of an average year for today’s buildings, not a forecast.
Does Portola Valley flood?
Flood insurance has paid 12 claims in Portola Valley since 1979, $650K in all, or 6.3 per 1,000 homes, more than 65% of U.S. towns with a flood insurance record. 2 properties have flooded more than once. The most claims came from Pineapple Express - Southern (5).
Is Portola Valley in a flood zone?
Flood zones are drawn street by street, so the answer depends on the address: look it up on FEMA’s flood map. In San Mateo County, 31% of homes in mapped flood zones carry federal flood insurance, and 1.8% of all homes do.
How much is flood insurance in Portola Valley?
FEMA’s Community Rating System list shows no discount for Portola Valley’s flood program. Premiums depend on the building; policies usually start 30 days after you buy, so get a quote early.
What was the biggest storm in Portola Valley?
By FEMA money that reached Portola Valley, Severe Winter Storms, Flooding, Landslides, and Mudslides (2022): 16 households applied for aid, $111K approved, and $112K to the Town of Portola Valley for repairs. By flood claims, Pineapple Express - Southern: 5 paid, $484K.
Is Portola Valley at risk from earthquakes?
It is the largest share of the building damage FEMA expects here (64%), and Portola Valley’s rate for it is in the top 2% of U.S. census tracts.
Storm stories
Memories, warnings and help from neighbors in Portola Valley.
Sources: FEMA National Risk Index v1.20 (December 2025), census-tract table, combined by where Portola Valley’s residents lived in the 2020 census; OpenFEMA: NFIP redacted claims, multiple-loss properties, community status book and residential penetration rates, housing assistance (owners and renters), public assistance funded projects, hazard mitigation properties and disaster declarations. Homes: Census ACS 2020–24. Preparedness tips: Ready.gov. FEMA’s model is an average of expected damage, not a forecast. How hazard risk is graded.