Photo: Wesoree · CC BY-SA 4.0Few places are as safe from hazards as Thornlea: it beats 88% of Canadian towns
Fire has left almost no mark near Thornlea: 0% of the land within 25 km since 1986, 0.001% a year. NRCan expects $0.034 of shaking damage a year per $1,000 of buildings in Thornlea, near the typical $0.030. Fewer homes than usual carry radon here, 0% over the guideline where the typical town has 6.6%. Hazard risk gives Thornlea a grade of A; its wildfire band pulls it down.
What stands out about Thornlea’s hazards
For Thornlea, from NRCan’s seismic model, Health Canada’s radon survey, the national burned-area record and the flood map inventory.
What Thornlea faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Thornlea grades A for hazard risk
The grade weighs Thornlea’s seismic risk and radon equally, and wildfire is one-sided: a high band counts against a town, a low one earns nothing.
Its place: #165 of 866 in Ontario and #484 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.
Wildfire is rare near Thornlea: 0% of the land within 25 km burned since 1986, 0% within 5 km
Fires mapped since 1986 around where Thornlea’s residents live, and the fuel next to their homes.
Low by Canadian standards: 0.001% of the land a year around Thornlea, 0.000% for the typical Canadian town.
The closest burn since 1986 lies 19 km from Thornlea’s homes, none within 5 km.
Forest makes up 0.2% of the land within 5 km of Thornlea and 4% within 25 km, little for a forest fire to run through.
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
Sioux Lookout burns fastest in Ontario at 0.16% a year; Thornlea, at 0.001%, ranks 83rd of 871.
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 Thornlea 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.
A flood study covers Thornlea, from Toronto Regional Conservation Authority: 1 on the inventory
Flood studies whose area touches Thornlea, from NRCan’s inventory, each linked to its owner.
One study on the inventory touches Thornlea, 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%; Thornlea has one too.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
The grade leaves flood out, since a study area says nothing about how many of Thornlea’s homes are at risk.
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.
Expected shaking damage in Thornlea: $0.034 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.
Nothing unusual about Thornlea’s ground: $0.034 against a typical $0.030, 1.1 times.
Shaking damage a year per $1,000 of building value
The typical town in Ontario expects $0.043 a year in shaking damage; Thornlea expects less, $0.034, and Alexandria the most, $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: 46% of Canada’s 2,611 towns have more earthquake risk than Thornlea.
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 Thornlea 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). · Data for earthquake risk covers the city of Markham
Little radon around Thornlea: 0% of area homes over the guideline
Health Canada’s survey of long-term home tests: the share above the 200 Bq/m³ guideline.
Where the typical Canadian town has 6.6% of homes over the guideline, Thornlea’s area has fewer, 0%.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Against the typical town in Ontario (4%), the area around Thornlea has fewer high tests: 0%.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
The quietest radon band, under 5%, holds 37% of Canada’s 2,611 towns and Thornlea; 63% sit higher.
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.
Whatever Thornlea’s area share, the reading that matters is your own home’s, over a winter.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011). · Radon tests: the York Regional Health Unit
Where to get warnings in Thornlea
Environment and Climate Change Canada issues the weather alerts for Thornlea; 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 Thornlea 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 Thornlea’s neighbours compare on hazards
The same four hazards for the places next door.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Thornlea | Low | $0.034 | 0% | Yes |
| German Mills 11,923 · 2.0 km | Low | $0.034 | 0% | Yes |
| Langstaff 8,147 · 2.3 km | Low | $0.034 | 0% | Yes |
| Steeles Corners 9,468 · 2.8 km | Low | $0.034 | 0% | Yes |
| Bayview Woods-Steeles 12,499 · 3.6 km | Low | $0.043 | 2.7% | Yes |
| Hillcrest Village 16,374 · 3.9 km | Low | $0.043 | 2.7% | Yes |
| Newtonbrook East 15,996 · 4.0 km | Low | $0.043 | 2.7% | Yes |
None of the places around has more fire nearby than Thornlea (low); German Mills comes closest (low).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Thornlea faces
What to do about the hazards Thornlea faces, and what to ask before you buy.
- 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 Thornlea is its health region’s, the survey’s design unit.
- 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 Thornlea.
- 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 Thornlea.
- Earthquakes are modelled. The earthquake figure is an expected loss, not a forecast, worked out by NRCan for each census subdivision, Thornlea’s included.
Questions about flooding and hazards in Thornlea
Is Thornlea at risk of wildfire?
Less than most of Canada: 0% of the land within 25 km of Thornlea has burned since 1986, the last in 2001, a low band that leaves Risk alone.
How is Thornlea’s Hazard risk Grade worked out?
Thornlea’s Hazard risk grade is A, built on earthquakes and radon with a one-sided wildfire input.
How big is the earthquake risk in Thornlea?
About $0.034 a year per $1,000 of building value, NRCan’s long-run expectation for Thornlea.
Is radon a problem in Thornlea?
In Health Canada’s survey, 0% of 95 homes tested in Thornlea’s area were above 200 Bq/m³, though only a test tells you about one house.
Does Thornlea flood?
There is flood mapping for Thornlea on the national inventory, each study linked to its owner’s map, none of them graded.
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).