Mariposa County, CA: home risks and climate
FEMA’s National Risk Index rates Mariposa County “Relatively Moderate” for overall risk relative to other US counties, 43rd of 58 counties in California by risk score. The hazards rated Relatively High or Very High here are landslide, wildfire and heat wave. These are relative ratings, not probabilities.
Mariposa County, CA
- Clear dead leaves and needles from gutters, the roof and under decks.
- Keep the first 5 feet around the house free of anything that burns (mulch, firewood, plants).
- Cover vents with 1/8-inch metal mesh to keep embers out.
- Service the AC before the hot season and clear the outdoor unit of debris.
- Change the AC filter; a clogged filter cuts cooling.
- Plan a cool place to go if the power or AC fails.
- Watch for new cracks in the ground, tilting trees or fences, and doors that stick.
- Keep gutters and drains directing water away from slopes.
- Know the signs of a debris flow during heavy rain.
- Use surge protection for electronics; ask an electrician about a whole-home surge protector.
- Keep trees near the house healthy and trimmed.
- Unplug sensitive electronics before a storm if you can.
- Clean gutters so melting snow drains instead of forming ice dams.
- Check attic insulation and air sealing; warm attics cause ice dams.
- Keep a snow shovel, ice melt and a backup heat plan.
- Watch for new cracks in foundations, walls and door frames; drought shrinks clay soils.
- Fix running toilets and dripping faucets.
- If you have a well, know its depth and recent yield.
- Look up your FEMA flood zone, and remember that "minimal hazard" zones still flood.
- Raise or move valuables, the furnace and the water heater off a basement floor where you can.
- Test the sump pump and its backup before the wet season.
- Strap the water heater to the wall with two straps.
- Secure tall furniture and TVs to studs.
- Know how to shut off gas at the meter, and only do it if you smell gas.
- Pick the safe room: lowest floor, interior, no windows. Tell everyone in the house.
- Keep shoes, a flashlight and a helmet for each person there.
- Turn on wireless emergency alerts on every phone.
- Trim dead or overhanging branches before storm season.
- Check that gutters, siding and roof edges are fastened tight.
- Tie down or store outdoor furniture, grills and trampolines.
- Photograph the roof and siding now, so you have a dated before picture.
- Ask about impact-rated (UL 2218 Class 4) shingles when the roof is replaced.
- Know your policy’s wind and hail deductible in dollars.
- Know if you are in a lahar or ashfall zone.
- Keep N95 masks and goggles for ash.
- Have a plan to protect the HVAC system from ash.
- Know whether your home or access road crosses avalanche paths.
- Follow local avalanche center forecasts in winter.
- Keep supplies for being snowed in for several days.
Winterize outdoor faucets before ~Nov 1. Typical first 32°F night (50% date) at Yosemite Village 12 W, 22 km away. Last freeze ~May 12.
Radon Zone 2: moderate predicted indoor radon. EPA recommends testing every home, whatever the zone.
- This monthPress the test button on every smoke and CO alarm.
- This monthCheck the date on the back of every smoke and CO alarm.
- This monthLook under every sink and around toilets and the water heater for drips.
- WatchLook in the attic with a flashlight after the first big storm of the season.
- WatchStock a power-outage kit: flashlights, batteries, water, a battery radio.
What the records say
Plain-language summary of the numbers below, compared with California and the US.
By FEMA’s hazard scores (0 to 100, the share of US counties scoring lower), landslide scores 99.5, wildfire scores 99.0 and heat wave scores 98.4 in Mariposa County, and modeled expected annual losses from all hazards come to about $38.1 million a year across 17,060 residents.
There have been 24 federal disaster declarations covering Mariposa County in the OpenFEMA record, close to the California county median of 24 and above the national county median of 20; 13 came in the last ten years. The most recent was french fire (2024-07-05).
Mariposa County sits in climate zone 4B (mixed-dry) in the mixed-dry Building America region and EPA radon zone 2.
At Yosemite Village 12 W (22 km from the county’s center), the typical first 32°F night is around Nov 1 and the last around May 12 (50% dates, 1991–2020), which sets when to winterize outdoor faucets.
All 18 hazards
FEMA National Risk Index December 2025. Ratings and scores are relative to other US counties, not probabilities. Expected annual loss is FEMA’s modeled average across buildings, people and agriculture.
| Hazard | Risk rating | Risk score | Expected annual loss | Recorded events | Prepare |
|---|---|---|---|---|---|
| Landslide | Relatively High | 99.5 | $1.7M | — | Checklist |
| Wildfire | Relatively High | 99.0 | $15.4M | — | Checklist |
| Heat wave | Relatively High | 98.4 | $11.2M | 62 | Checklist |
| Winter weather | Relatively Moderate | 77.1 | $113,167 | 239 | Checklist |
| Drought | Relatively Moderate | 75.5 | $447,672 | 2,324 | Checklist |
| Lightning | Relatively Moderate | 69.2 | $302,329 | 22,115 | Checklist |
| Inland flooding | Relatively Low | 70.8 | $8.4M | 58 | Checklist |
| Earthquake | Relatively Low | 67.5 | $432,731 | — | Checklist |
| Volcanic activity | Very Low | 58.6 | $17 | 4 | Checklist |
| Avalanche | Very Low | 40.5 | $171 | 0 | Checklist |
| Strong wind | Very Low | 10.8 | $49,836 | 2 | Checklist |
| Hail | Very Low | 6.6 | $11,836 | 6 | Checklist |
| Tornado | Very Low | 6.4 | $18,388 | 2 | Checklist |
| Cold wave | No Rating | 0.0 | $0 | 0 | Checklist |
| Hurricane | Not Applicable | — | — | — | Checklist |
| Coastal flooding | Not Applicable | — | — | — | Checklist |
| Ice storm | Not Applicable | — | — | — | Checklist |
| Tsunami | Not Applicable | — | — | — | Checklist |
Federal disaster declarations
Each county-level declaration in OpenFEMA DisasterDeclarationsSummaries v2, counted once per disaster number.
| Declared | Event | Type |
|---|---|---|
| 2024-07-05 | French fire | FM · Fire |
| 2023-04-03 | Severe winter storms, straight-line winds, flooding, landslides, and mudslides | DR · Severe Storm |
| 2023-03-10 | Severe winter storms, flooding, landslides, and mudslides | EM · Flood |
| 2023-01-14 | Severe winter storms, flooding, landslides, and mudslides | DR · Flood |
| 2023-01-09 | Severe winter storms, flooding, and mudslides | EM · Flood |
| 2022-07-23 | Oak fire | FM · Fire |
| 2020-03-22 | COVID-19 pandemic | DR · Biological |
| 2020-03-13 | COVID-19 | EM · Biological |
| 2019-05-17 | Severe winter storms, flooding, landslides, and mudslides | DR · Severe Storm |
| 2019-05-01 | Severe winter storms, flooding, landslides, and mudslides | DR · Severe Storm |
| 2017-09-02 | Railroad fire | FM · Fire |
| 2017-07-17 | Detwiler fire | FM · Fire |
Showing the 12 most recent of 24.
Flood-insurance claims (NFIP)
Claims filed under the National Flood Insurance Program, from FEMA’s NfipClaims v3 dataset (all years on file), by year of loss.
Climate, radon and freeze
This month’s plan for Mariposa County
Region tasks plus this county’s hazard ratings and freeze dates. Add your ZIP and systems on the Home Plan page to subscribe in your calendar.
November5 tasks
- This monthPress the test button on every smoke and CO alarm.
An alarm you have not heard in months may have a dead battery or sensor. NFPA recommends testing smoke alarms at least once a month.
How
Hold the test button until it sounds. Anything silent or chirping: replace the battery, or the whole alarm if it is past its date.
- This monthCheck the date on the back of every smoke and CO alarm.
Smoke alarms wear out: NFPA advises replacing them 10 years after the manufacture date. CO alarms have their own end-of-life date printed on them.
How
Twist each alarm off its base and read the date. Replace any past its life; swap batteries in alarms that take them.
- This monthLook under every sink and around toilets and the water heater for drips.
Slow leaks rot cabinets and subfloors long before they show. Catching one early is a washer, not a floor.
How
Use a flashlight: feel supply lines and the shutoff valves, look for stains, warped cabinet floors or a toilet that rocks.
- WatchLook in the attic with a flashlight after the first big storm of the season.
Stains on the roof deck, wet insulation or daylight around vents show leaks early, and droppings show pests.
How
Stay on the joists. Look around chimneys, vent pipes and valleys, the places most leaks start.
- WatchStock a power-outage kit: flashlights, batteries, water, a battery radio.
Winter storms bring multi-day outages.
How
Keep it in one bin. Add a phone power bank and a list of medicines that need power or refrigeration.
December2 tasks
- This monthPress the test button on every smoke and CO alarm.
An alarm you have not heard in months may have a dead battery or sensor. NFPA recommends testing smoke alarms at least once a month.
How
Hold the test button until it sounds. Anything silent or chirping: replace the battery, or the whole alarm if it is past its date.
- WatchDegrease the range-hood filter.
Grease-clogged hood filters stop pulling smoke and grease out of the kitchen and can feed a stovetop fire.
How
Pop the metal filter out and soak it in hot water with dish soap and baking soda, or run it through the dishwasher if the maker allows.
Neighbouring counties
Information, not insurance, legal or engineering advice. Ratings describe the county as a whole; your address can differ. Found an error? Send a correction.