Photo: Skytrain3514 at English Wikipedia · Public domainHazards in Thornbury: wildfire low, radon over the guideline in 11% of tested homes
The national fire record shows next to nothing around Thornbury, 0% of the land within 25 km since 1986 (0.000% a year). Shaking is less of a worry than in most places, at $0.010 a year per $1,000 of building value ($0.030 typical). Thornbury grades B+ for hazard risk; wildfire is low here, so it earns no credit.
What stands out about Thornbury’s hazards
For Thornbury, from NRCan’s seismic model, Health Canada’s radon survey, the national burned-area record and the flood map inventory.
What Thornbury faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Hazard risk in Thornbury: B+
Earthquake risk and radon make Thornbury’s grade; wildfire can only lower it, never raise it, and flood studies are listed but not scored.
Its place: #599 of 866 in Ontario and #1,362 of 2,589 Canadian towns.
How sure: Earthquake losses are a model’s expectation over many years, not a forecast for any one. The burned-area record misses fires under about 10 ha and most grass and farm fires.
Few fires near Thornbury: 0% within 5 km, 0% within 25 km
Fires mapped since 1986 around where Thornbury’s residents live, and the fuel next to their homes.
Low by Canadian standards: 0.000% of the land a year around Thornbury, 0.000% for the typical Canadian town.
About as much forest grows next to Thornbury’s homes (12% within 5 km) as across 25 km (16%).
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); Thornbury 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%), Thornbury 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.
No flood study is listed for Thornbury
Flood studies whose area touches Thornbury, from NRCan’s inventory, each linked to its owner.
Nationally, Thornbury has no listed flood study; the municipality is the place to ask.
Towns with a flood study on file
Mapping in Ontario reaches 69% of towns, beside 58% across Canada, but not Thornbury.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Flood mapping is shown for Thornbury to be opened and checked, never turned into a grade.
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.”
Little shaking expected in Thornbury: $0.010 a year per $1,000
NRCan’s seismic risk model: the damage shaking is expected to do to buildings each year, on average over many years.
Shaking costs the typical town $0.030 a year; in Thornbury it is only $0.010, 0.3 times as much.
Shaking damage a year per $1,000 of building value
Below the middle in Ontario: Thornbury’s $0.010 against a median of $0.043; Alexandria has $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.
Thornbury is in the lower part of Canada’s range for earthquake risk; 86% of the 2,611 towns are higher.
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).
Only shaking damage to buildings in Thornbury is counted; landslides, liquefaction, tsunami and fire after a quake aren’t.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
Test for radon in Thornbury: 11% of area homes were over the guideline
Health Canada’s survey of long-term home tests: the share above the 200 Bq/m³ guideline. · Measured across the Grey Bruce Health Unit: radon tests
the typical Canadian town has 6.6% over the guideline; Thornbury’s area has 11%.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Thornbury’s area, at 11%, is above the median in Ontario (4%), and 1% of its tests passed 600 Bq/m³.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
4.6% of Canada’s 2,611 towns have a higher share of homes over 200 Bq/m³ than Thornbury, in the 10–20% band with 22%.
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.
Health Canada advises testing every home, Thornbury’s included, whatever the area’s figure.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Where to get warnings in Thornbury
Alerts for Thornbury 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 Thornbury 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)
Hazards in the places around Thornbury
The same four hazards for the places next door.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Thornbury | Low | $0.010 | 11% | None listed |
| Collingwood 28,366 · 17 km | Low | $0.016 | 0.9% | None listed |
Collingwood (low) has the heaviest fire record of Thornbury’s neighbours, and Thornbury (low) matches or beats it.
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Thornbury faces
Practical steps for Thornbury’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?
- Ask the municipality for flood maps.
- Are flood and wildfire insured?
What this data can and can’t tell you
- Radon is a survey. Health Canada’s survey tested some 14,000 homes over three months; until postal-area boundaries are loaded, Thornbury takes its 2007 health region’s share.
- Wildfire counts one way. Burned land within 25 km of where people live, averaged over 1986–2025 and checked for fuel near homes, is the measure; it looks back, not ahead, and only ever counts against Thornbury.
- Earthquakes are modelled. The earthquake figure is an expected loss, not a forecast, worked out by NRCan for each census subdivision, Thornbury’s included.
- Flood studies aren’t flood zones. The flood inventory points to maps; it is incomplete and not the official source, so ask the municipality about any street in Thornbury.
Questions about flooding and hazards in Thornbury
How is Thornbury’s Hazard risk Grade worked out?
Hazard risk gives Thornbury B+, weighing earthquakes and radon and counting wildfire only against it.
Is radon a problem in Thornbury?
The area’s survey found 11% of 98 tested homes above Health Canada’s guideline, so a three-month test is worth doing in Thornbury.
How big is the earthquake risk in Thornbury?
About $0.010 a year per $1,000 of building value, NRCan’s long-run expectation for Thornbury.
Is Thornbury at risk of wildfire?
No meaningful wildfire history near Thornbury: 0% of nearby land since 1986, band low.
Does Thornbury flood?
The inventory has 0 studies for Thornbury, and an empty list isn’t a clean bill: the municipality holds any flood maps.
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).