FEMA puts San Lorenzo’s expected hazard damage per building above that of 95% of U.S. towns, mostly from earthquakes
On FEMA’s National Risk Index, San Lorenzo gets a D for hazard risk: higher expected damage per building than 95% of U.S. towns, #558 of 847 in California. Most of that expected damage is earthquakes (62%), then river and rain flooding (38%). Flood insurance has paid 2 claims here since 2002.
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 San Lorenzo 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
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 San Lorenzo’s grade
Earthquakes are 62% of the building damage FEMA expects in San Lorenzo, and San Lorenzo’s rate of earthquakes damage is in the top 2% of U.S. census tracts. Next is river and rain flooding at 38% (higher than 82% of U.S. census tracts).
D #558 of 847 in California; higher expected damage per building than 95% of U.S. towns (21,298).
San Lorenzo’s residents live in 6 census tracts; FEMA’s figures are combined by where they live.
The typical California town has higher expected damage than 92% of U.S. towns; within the state, San Lorenzo has more expected damage per building than 66% of California towns.
In dollars, FEMA expects about $20.3M a year in losses across San Lorenzo: $13.7M to buildings, the rest to people and crops.
Does San Lorenzo flood? Rarely: 2 flood claims since 2002
Every paid claim on a federal flood insurance policy in San Lorenzo, from FEMA’s records: 0.2 per 1,000 homes, fewer than 97% of the 13,809 U.S. towns with a flood insurance record.
- The California Atmospheric River1 claim · $10K
San Lorenzo isn’t in FEMA’s Community Rating System, which cuts flood insurance up to 45% in towns that do extra flood-proofing.
Insurance rates: Alameda County.The storms San Lorenzo remembers
None of the 20 disasters declared for Alameda County shows FEMA aid or repair money reaching San Lorenzo itself in FEMA’s records, so these are its biggest flood-claim years.
- 20021 flood claims paidNo declaration for the county that year
- 20231 flood claims paidThe year of Severe Winter Storms, Straight-line Winds, Flooding, Landslides, and Mudslides, declared for Alameda County
Alameda County has had 20 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.
Old photos of San Lorenzo after a storm or flood belong in the town’s history. Add one, or share what you remember below.
Add to the San Lorenzo archive →San Lorenzo and its neighbors
San Lorenzo is 3rd of the 5 graded towns here, from least expected damage per building to most. Tap a town to see its hazards.
| Town | Hazard risk | Mostly (buildings) | Flood claims |
|---|---|---|---|
| Ashland | Dmore damage than 93% | earthquakes | 1 |
| Cherryland | Dmore damage than 94% | earthquakes | — |
| San Lorenzo | Dmore damage than 95% | earthquakes | 2 |
| Hayward | Dmore damage than 95% | earthquakes | 16 |
| San Leandro | D−more damage than 97% | earthquakes | 5 |
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 San Lorenzo 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.
- 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 San Lorenzo
Is San Lorenzo at risk for natural disasters?
On FEMA’s National Risk Index, San Lorenzo has higher expected damage per building than 95% of U.S. towns: D for hazard risk, #558 of 847 in California. Most of the expected damage is earthquakes (62%) and river and rain flooding (38%). This is FEMA’s model of an average year for today’s buildings, not a forecast.
Does San Lorenzo flood?
Flood insurance has paid 2 claims in San Lorenzo since 2002, $32K in all, or 0.2 per 1,000 homes, fewer than 97% of U.S. towns with a flood insurance record. The most claims came from California Atmospheric River (1).
Is San Lorenzo 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 Alameda County, 36% of homes in mapped flood zones carry federal flood insurance, and 0.8% of all homes do.
How much is flood insurance in San Lorenzo?
FEMA’s Community Rating System list shows no discount for San Lorenzo’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 San Lorenzo?
By flood claims, California Atmospheric River: 1 paid, $10K.
Is San Lorenzo at risk from earthquakes?
It is the largest share of the building damage FEMA expects here (62%), and San Lorenzo’s rate for it is in the top 2% of U.S. census tracts.
Storm stories
Memories, warnings and help from neighbors in San Lorenzo.
Sources: FEMA National Risk Index v1.20 (December 2025), census-tract table, combined by where San Lorenzo’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.