Flood Risk in San Mateo, CA: 124 FEMA Claims
San Mateo has significant flood risk — 80% of ZIP codes are in FEMA flood zones.
80% of ZIPs in flood zones · 124 FEMA claims · Updated 2026-05-03
Data: FEMA National Flood Insurance Program (NFIP), FEMA Hazard Mitigation Last verified: 2026-05-03
Historically, FEMA has documented 124 flood claims for San Mateo. Each of those claims was paid out under a dedicated flood policy — not a home insurance policy, which does not include flood coverage.
What are FEMA flood zones?
FEMA classifies areas into flood zones based on the probability of flooding. High-risk zones (A and V) have a 1% annual chance of flooding and require flood insurance for federally-backed mortgages. Moderate-risk zones (B/X shaded) have a 0.2% annual chance. Even in low-risk zones, about 25% of all flood claims come from areas outside designated high-risk zones. San Mateo has 80% of ZIP codes in designated flood zones.
How are flood insurance claims calculated?
FEMA tracks every claim filed through the National Flood Insurance Program (NFIP). Claims data includes payouts for building damage and contents loss. High claim counts in an area indicate actual flood events, not just theoretical risk. San Mateo has 124 recorded claims — this real-world history is often a better risk indicator than flood zone maps alone.
Flood Risk Overview
San Mateo, California has 80% of its ZIP codes located in FEMA-designated flood zones. A total of 124 flood insurance claims have been filed through the National Flood Insurance Program (NFIP), with $931K in total payouts.
The average payout per claim is $8K, reflecting the typical cost of flood damage in the San Mateo area.
Understanding Flood Zones
FEMA classifies areas into flood zones based on risk:
| Zone | Risk Level | Description |
|---|---|---|
| A, AE, AH, AO | High | 1% annual chance of flooding (100-year floodplain) |
| V, VE | Very High | Coastal areas with wave action |
| B, X (shaded) | Moderate | 0.2% annual chance (500-year floodplain) |
| C, X (unshaded) | Low | Minimal flood risk |
Important: Even "low risk" areas experience flooding. Over 40% of NFIP claims come from outside high-risk zones.
Flood Insurance in San Mateo
Standard homeowner's insurance does not cover flood damage. Options include:
National Flood Insurance Program (NFIP)
- Available through any insurance agent
- Maximum coverage: $250,000 for building, $100,000 for contents
- Average annual premium: $700–$1,500
- 30-day waiting period before coverage begins
Private Flood Insurance
- Often more coverage at lower premiums
- Faster claims processing
- May offer replacement cost coverage (NFIP pays actual cash value)
Required? If you have a federally backed mortgage and are in a Special Flood Hazard Area (SFHA), flood insurance is mandatory.
How Flooding Affects Drinking Water
Flooding poses direct threats to drinking water quality:
- Water treatment plant overflow — systems can be overwhelmed, leading to untreated or partially treated water
- Sewage contamination — floodwater mixes with sewage systems, introducing bacteria and pathogens
- Agricultural runoff — pesticides, fertilizers, and animal waste enter water supplies
- Well contamination — private wells are especially vulnerable to floodwater infiltration
- Infrastructure damage — pipes can break, creating entry points for contaminants
After a flood event, always follow local boil water advisories and avoid using tap water until the all-clear is given.
FEMA Flood Map for San Mateo
To check your exact flood zone designation in San Mateo, use the official FEMA Flood Map Service Center:
- FEMA Flood Map Service Center — enter your address to see your flood zone
- FEMA National Flood Hazard Layer — interactive map viewer
Flood zone distribution of claims in San Mateo:
| FEMA Zone | Claims | Risk Level |
|---|---|---|
| X | 40 | Moderate-Low |
| A | 25 | High (100-yr floodplain) |
| AE | 18 | High (100-yr floodplain) |
| C | 15 | Minimal |
| AO | 5 | High (100-yr floodplain) |
| A99 | 3 | High (100-yr floodplain) |
NFIP Claims History
| Metric | Value |
|---|---|
| Total claims filed | 124 |
| Total payouts | $931K |
| Average per claim | $8K |
| Recent claims (last 5 years) | 49 |
| Recent payouts | $729K |
| ZIP codes monitored | 5 |
| Population | 157 |
40% of all claims were filed in the last 5 years.
Financial Impact of Flooding in San Mateo
Flooding in San Mateo has resulted in $931K in total FEMA payouts across 124 claims.
| Impact Metric | Value |
|---|---|
| Average claim amount | $8K |
| Total FEMA payouts | $931K |
| Claims per 1,000 residents | 789.8 |
| Payouts per capita | $6K |
Property value impact: Homes in FEMA-designated flood zones typically sell for 4–7% less than comparable homes outside flood zones. Mandatory flood insurance requirements add $700–$1,500/year in carrying costs.
Weather Alerts & Flood Warnings
The National Weather Service (NWS) issues flood watches and warnings for the San Mateo area. Monitor these resources:
- NWS Weather Alerts — real-time severe weather alerts by location
- Weather.gov California — state-level active alerts
- FEMA Emergency Alerts — IPAWS integrated alerts
Alert types for San Mateo area:
| Alert Type | Meaning | Action |
|---|---|---|
| Flood Watch | Flooding is possible | Prepare to move to higher ground |
| Flood Warning | Flooding is occurring or imminent | Take action immediately |
| Flash Flood Warning | Flash flooding within hours | Move to high ground now |
| Coastal Flood Advisory | Minor coastal flooding | Monitor conditions |
Set up Wireless Emergency Alerts (WEA) on your phone to receive automatic flood warnings for San Mateo.
Protecting Your Home from Flooding
Before a flood:
- Know your flood zone — check FEMA's map
- Install sump pump with battery backup
- Elevate electrical systems, furnace, and water heater above potential flood levels
- Apply waterproof sealant to basement walls and floors
- Keep gutters and downspouts clear
During a flood:
- Move to higher ground immediately
- Do not walk or drive through floodwater
- Turn off utilities if instructed
- Monitor local emergency alerts
After a flood:
- Do not drink tap water until the boil water advisory is lifted
- Document damage with photos for insurance claims
- Watch for mold growth in the following weeks
- Have your water tested before resuming normal use
Flood Risk by ZIP Code
Flood claims and zone designations vary across San Mateo's ZIP codes:
| ZIP Code | FEMA Claims | Total Paid | Zone |
|---|---|---|---|
| 94401 | 48 | $87K | A |
| 94403 | 43 | $334K | X |
| 94404 | 20 | $374K | X |
| 94402 | 13 | $135K | X |
ZIP code 94401 has the most flood claims (48) with $87K in total payouts.
ZIP Codes in San Mateo
San Mateo covers 5 ZIP codes. Flood risk varies by ZIP code based on elevation, proximity to water bodies, and drainage infrastructure. Check your specific ZIP code for detailed flood zone mapping.
Data Sources
- Flood claims: FEMA National Flood Insurance Program (NFIP)
- Flood zones: FEMA Flood Map Service Center
- Water quality impact: EPA Emergency Response guidance
Updated daily.
Water Quality Map: San Mateo, CA
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Flood Risk by ZIP Code in San Mateo
Flood risk varies across San Mateo's 5 ZIP codes based on elevation, proximity to water bodies, and drainage infrastructure.
| ZIP Code | Grade | Score | Violations | |
|---|---|---|---|---|
| 94401 | C | 66/100 | 4 | View report → |
| 94402 | C | 66/100 | 4 | View report → |
| 94403 | C | 66/100 | 4 | View report → |
| 94404 | C | 66/100 | 4 | View report → |
| 94497 | C | 68/100 | 4 | View report → |