Photo: Skeezix1000 · CC BY-SA 3.0Hazard risk in Gravenhurst is lower than in 89% of Canadian towns
Wildfire isn’t Gravenhurst’s worry: 0% of the land within 25 km burned since 1986 (0.000% a year). Seismic risk in Gravenhurst sits near the middle: $0.024 of expected damage per $1,000 of buildings a year, the typical town $0.030. Radon is lower than usual: 0.9% of tested homes in the survey area topped the guideline, against 6.6% for the typical town. Hazard risk gives Gravenhurst a grade of A, from earthquakes and radon alone.
What stands out about Gravenhurst’s hazards
Four national sources, each read for Gravenhurst: earthquakes, radon, past fires and flood studies.
What Gravenhurst faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Hazard risk in Gravenhurst: A
Seismic risk and radon set Gravenhurst’s grade, wildfire can drag it down, and flood mapping stays out of it.
Its place: #104 of 866 in Ontario and #414 of 2,589 Canadian towns.
How sure: Earthquake losses are a model’s expectation over many years, not a forecast for any one. Small fires and grass fires are largely missing from the national burned-area record.
Wildfire is rare near Gravenhurst: 0% of the land within 25 km burned since 1986, 0% within 5 km
Fires mapped since 1986 around where Gravenhurst’s residents live, and the fuel next to their homes.
Around Gravenhurst fire takes 0.000% of the land in a typical year, the typical Canadian town 0.000%, which is low.
No fire has burned within 5 km of Gravenhurst’s homes since 1986; the nearest burn is 13 km away.
Forest fuel is denser close to Gravenhurst (39% within 5 km) than further out (25% within 25 km).
Shares of land within 5 and 25 km of populated blocks: burned at least once in 1986–2025 (CWFIS burned-area composite), forest fuel and grass (fire behaviour fuel types, 2026, 250 m grid).
Burn rate a year, towns in Ontario · highest of 871
Among the 871 towns in Ontario, Sioux Lookout burns fastest (0.16% a year); Gravenhurst is with the 638 near zero.
Each bar: the yearly average share of land within 25 km of a town’s homes that burned, 1986–2025 (CWFIS); the seven highest towns of 2,500 people or more.
Like most of Canada’s 2,610 towns (92%), Gravenhurst is in the low band, with a burn rate of zero to three decimals; 7.5% rank higher.
Bands of the yearly burn rate: low under 0.05%, moderate under 0.25%, high under 1%, very high 1% or more; towns of 2,500 people or more.
Fire danger and active fires (CWFIS)
Canadian Wildland Fire Information System: National Burned Area Composite 1986–2025 and fire behaviour fuel types (2026), Natural Resources Canada. Measured within 25 km and 5 km of each populated dissemination area; past fire, not a forecast.
A flood study covers Gravenhurst, from District Municipality of Muskoka: 1 on the inventory
Flood studies whose area touches Gravenhurst, from NRCan’s inventory, each linked to its owner.
District Municipality of Muskoka studied flooding in an area that includes Gravenhurst (2024); open its map to see which streets lie in a flood zone.
| Study | By | Year | Status |
|---|---|---|---|
| District of Muskoka Floodplain Mapping | District Municipality of Muskoka | 2024 | final |
Towns with a flood study on file
Gravenhurst is one of the 69% of towns in Ontario with a flood study on file; across Canada it is 58%.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Listed, not scored: a flood study proves a map exists, not that Gravenhurst floods.
The inventory’s own caution (NRCan): “The Canada Flood Map (CFM) does not include every flood hazard map in Canada and may be incomplete or contain inaccuracies. It should not be relied upon as the official source of flood mapping information. Furthermore, if a map appears to be missing, this does not necessarily mean that the area has never been mapped. For the official version of a map, updated information, or confirmation of applicable regulations, please contact the local authority responsible for flood mapping.”
Natural Resources Canada, Canada Flood Map Inventory; links go to each study’s owner.
Earthquakes cost buildings in Gravenhurst $0.024 per $1,000 a year
NRCan’s seismic risk model: the damage shaking is expected to do to buildings each year, on average over many years.
Gravenhurst’s $0.024 is close to the typical town’s $0.030 (0.8 times as much).
Shaking damage a year per $1,000 of building value
Gravenhurst’s $0.024 sits under the median in Ontario, $0.043, and well under Alexandria’s $0.21.
NRCan seismic risk model (2022): mean yearly building loss per $1,000 of value; medians of towns of 2,500 people or more.
Neither high nor low for Canada: 54% of the 2,611 towns expect more damage than Gravenhurst.
Each column: the share of Canada’s towns of 2,500 people or more in that range of yearly loss per $1,000 (NRCan, 2022).
The model counts damage to Gravenhurst’s buildings and their occupants from shaking only: not liquefaction, landslides, tsunami or fires after a quake.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
Radon runs low around Gravenhurst: 0.9% of tested homes over the guideline
Health Canada’s survey of long-term home tests: the share above the 200 Bq/m³ guideline.
Radon runs below the typical Canadian town (6.6%) in Gravenhurst’s area, at 0.9%. Gravenhurst doesn’t get its own radon tests figures; the ones here come from the Simcoe Muskoka District Health Unit.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
The median in Ontario is 4% over 200 Bq/m³; around Gravenhurst it is 0.9%.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
Few tests over the guideline: Gravenhurst shares the bottom band with 37% of Canada’s 2,611 towns, below the other 63%.
Each bar: the share of Canada’s towns of 2,500 people or more whose survey area had that share of tests over 200 Bq/m³.
One home in Gravenhurst can be high while next door is low; a three-month test settles it.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Weather and fire alerts for Gravenhurst
Alerts for Gravenhurst come from Environment and Climate Change Canada and, for emergencies, Alert Ready.
| Alert | What it means |
|---|---|
| Warning | Severe weather is happening or about to: act now. |
| Watch | Conditions favour severe weather: be ready. |
| Advisory | Weather that is less severe but could disrupt the day. |
| Special weather statement | Unusual weather worth knowing about. |
| Special air quality statement | Poor air, often wildfire smoke. |
Fire danger and active fires near Gravenhurst are mapped daily by the Canadian Wildland Fire Information System; evacuation orders come from the municipality or province.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
How Gravenhurst’s neighbours compare on hazards
The same four hazards for the places next door.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Gravenhurst | Low | $0.024 | 0.9% | Yes |
| Bracebridge 18,676 · 16 km | Low | $0.023 | 0.9% | Yes |
Nowhere around Gravenhurst burns more: Bracebridge, the closest rival, is low to its low.
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Gravenhurst faces
Practical steps for Gravenhurst’s hazards, most pressing first.
- Test for three months in winter.
- Over 200 Bq/m³: fix it.
- Kits are cheap; pros test too.
- Never drive through floodwater.
- Move papers and medicines upstairs.
- Ask whether your street is mapped.
- Clear needles and wood nearby.
- Keep a grab-and-go bag ready.
- In smoke, stay in; filter air.
- Has it had a radon test?
- Check the address on the flood map.
- Are flood and wildfire insured?
What this data can and can’t tell you
- Radon is a survey. About 14,000 homes were tested across Canada in 2009–2011, and the share over the guideline for Gravenhurst is its health region’s, the survey’s design unit.
- Wildfire counts one way. Wildfire is read from the national burned-area record around Gravenhurst’s homes since 1986, a history of fire that may lower Risk but never raises it.
- Flood studies aren’t flood zones. NRCan’s inventory says where flood mapping exists, not where water goes; the map’s owner is the authority for Gravenhurst.
- Earthquakes are modelled. NRCan models what earthquakes would cost buildings each year on average, subdivision by subdivision; Gravenhurst’s figure is its subdivision’s.
Questions about flooding and hazards in Gravenhurst
Is Gravenhurst at risk of wildfire?
Not much by Canadian standards: Gravenhurst’s band is low, with 0% of the land within 25 km burned since 1986 (last in 2016), so wildfire doesn’t change its grade.
Does Gravenhurst flood?
There is flood mapping for Gravenhurst on the national inventory, each study linked to its owner’s map, none of them graded.
How is Gravenhurst’s Hazard risk Grade worked out?
Gravenhurst grades A for hazard risk, from earthquakes and radon, with wildfire counted only where it lowers the grade.
How big is the earthquake risk in Gravenhurst?
About $0.024 a year per $1,000 of building value, NRCan’s long-run expectation for Gravenhurst.
Is radon a problem in Gravenhurst?
0.9% of the 109 homes Health Canada tested around Gravenhurst topped the guideline; your own house needs its own test.
Seismic risk: Natural Resources Canada. Radon: Health Canada. Wildfire: Canadian Wildland Fire Information System. Flood studies: Natural Resources Canada, Canada Flood Map Inventory. Contains information licensed under the Open Government Licence – Canada.
Sources: NRCan, Canada’s Seismic Risk Model 2022 · Health Canada, Cross-Canada Survey of Radon Concentrations in Homes · CWFIS, National Burned Area Composite and FBP fuel types · NRCan, Canada Flood Map Inventory. Under the Statistics Canada Open Licence.
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).