Photo: Canmenwalker · CC BY 4.0Hazard risk in Thornhill is lower than in 90% of Canadian towns
Since 1986 almost nothing has burned near Thornhill: 0% of the land within 25 km, or 0.001% a year. NRCan expects $0.028 of shaking damage a year per $1,000 of buildings in Thornhill, near the typical $0.030. In Health Canada’s survey, just 0% of homes tested in the area exceeded 200 Bq/m³ (6.6% typical). Thornhill grades A for hazard risk, with wildfire counted against it.
What stands out about Thornhill’s hazards
For Thornhill, from NRCan’s seismic model, Health Canada’s radon survey, the national burned-area record and the flood map inventory.
What Thornhill faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Thornhill grades A for hazard risk
Seismic risk and radon set Thornhill’s grade, wildfire can drag it down, and flood mapping stays out of it.
Its place: #74 of 866 in Ontario and #383 of 2,589 Canadian towns.
How sure: The seismic figure is a long-run average from NRCan’s model, not a prediction. The burned-area record misses fires under about 10 ha and most grass and farm fires.
Little of the land around Thornhill has burned: 0% within 5 km, 0% within 25 km since 1986
Past fire around Thornhill’s homes, from the national burned-area record, with the fuel within 5 km.
The land within 25 km of Thornhill burns at 0.001% a year on average, the low band; the typical Canadian town: 0.000%.
Fire has stayed at least 23 km from Thornhill’s homes since 1986.
With 0.3% forest fuel within 5 km and 3.5% within 25 km, the land around Thornhill gives a fire little to burn.
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
In the top quarter in Ontario: Thornhill ranks 83rd of 871 at 0.001% a year, with Sioux Lookout first at 0.16%.
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.
Low, like 92% of the country’s 2,610 towns: the land around Thornhill burns, but slower than in the 7.5% above it.
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.
Toronto Regional Conservation Authority has mapped flooding for Thornhill (1 study)
What Canada’s Flood Map Inventory lists for Thornhill: who studied flooding and where to see their maps.
One study on the inventory touches Thornhill, Toronto Regional Conservation Authority’s from 2021, and its area can be large, so it says a map exists, not that the town floods.
| Study | By | Year | Status |
|---|---|---|---|
| Toronto Floodline Consolidation | Toronto Regional Conservation Authority | 2021 | final |
Towns with a flood study on file
69% of towns in Ontario have a flood study, more than Canada’s 58%; Thornhill has one too.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Nothing here counts toward Risk; the studies are pointers to the maps their owners keep for Thornhill.
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.
Ordinary seismic risk in Thornhill: $0.028 per $1,000 of buildings a year
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
Nothing unusual about Thornhill’s ground: $0.028 against a typical $0.030, 0.9 times.
Figures for earthquake risk are published for the city of Vaughan as a whole, not for Thornhill alone.
Shaking damage a year per $1,000 of building value
At $0.028, Thornhill is below the typical town in Ontario ($0.043); Alexandria is highest at $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.
Middle of the pack: 51% of Canada’s 2,611 towns have more earthquake risk than Thornhill.
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 Thornhill 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).
Little radon around Thornhill: 0% of area homes over the guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
At 0% over the guideline, the area around Thornhill is under the typical Canadian town’s 6.6%. Thornhill doesn’t get its own radon tests figures; the ones here come from the York Regional Health Unit.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Fewer homes top the guideline around Thornhill (0%) than in the typical town in Ontario (4%).
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
63% of Canada’s 2,611 towns have a higher share of homes over 200 Bq/m³ than Thornhill’s band, which holds 37%.
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.
Radon varies from house to house in Thornhill, so the survey is a reason to test, not a result for yours.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Where to get warnings in Thornhill
Environment and Climate Change Canada issues the weather alerts for Thornhill; Alert Ready carries the urgent ones to phones, radio and TV.
| 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. |
Smoke and fire warnings for Thornhill come through Environment Canada and Alert Ready; the fire map is CWFIS’s.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
How Thornhill’s neighbours compare on hazards
Wildfire band, earthquake risk, radon and flood studies for each place nearby.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Thornhill | Low | $0.028 | 0% | Yes |
| Steeles Corners 9,468 · 1.5 km | Low | $0.034 | 0% | Yes |
| Beverley Glen 38,720 · 1.8 km | Low | $0.028 | 0% | Yes |
| Newtonbrook West 23,978 · 2.3 km | Low | $0.043 | 2.7% | Yes |
| Langstaff 8,147 · 2.4 km | Low | $0.034 | 0% | Yes |
| Newtonbrook East 15,996 · 2.5 km | Low | $0.043 | 2.7% | Yes |
| Westminster-Branson 26,027 · 2.9 km | Low | $0.043 | 2.7% | Yes |
Fire is no heavier anywhere nearby than around Thornhill (low), with Steeles Corners next at low.
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Thornhill faces
Practical steps for Thornhill’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. Radon figures pool the survey’s home tests by area: postal areas once their boundaries arrive, the 2007 health region around Thornhill until then.
- Earthquakes are modelled. Seismic risk is NRCan’s model of yearly building losses from shaking, averaged over many years and given for Thornhill’s census subdivision (a neighbourhood shows its city’s).
- Flood studies aren’t flood zones. Flood studies cover areas of every size, which is why the page lists them for Thornhill without grading them.
- Wildfire counts one way. For Thornhill, wildfire means how much nearby land burned in the past forty years, a one-way input that can pull Risk down and nothing more.
Questions about flooding and hazards in Thornhill
Does Thornhill flood?
A flood study covers Thornhill on Canada’s Flood Map Inventory; open the owner’s map to check a street, since flood isn’t graded.
Is radon a problem in Thornhill?
The area’s survey found 0% of 95 tested homes above Health Canada’s guideline, so a three-month test is worth doing in Thornhill.
How is Thornhill’s Hazard risk Grade worked out?
Thornhill grades A for hazard risk, from earthquakes and radon, with wildfire counted only where it lowers the grade.
Is Thornhill at risk of wildfire?
Some, but Thornhill’s low band (0% of nearby land burned since 1986, latest 2001) is short of the level that counts.
How big is the earthquake risk in Thornhill?
NRCan’s model expects shaking to cost buildings in Thornhill $0.028 a year for every $1,000 of their value, on average over many years.
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).