Photo: Roncanada · CC BY 4.0Flood mapping exists for Saint-Thomas: 1 on record, latest by MRC Joliette
Fire seldom reaches Saint-Thomas: since 1986, 0% of the land within 25 km has burned (0.001% a year). Seismic risk runs high: $0.15 of expected damage per $1,000 of buildings a year, the typical town $0.030. Radon is lower than usual: 3.9% of tested homes in the survey area topped the guideline, against 6.6% for the typical town. Saint-Thomas grades B− for hazard risk; wildfire is low here, so it earns no credit.
What stands out about Saint-Thomas’s hazards
For Saint-Thomas, from NRCan’s seismic model, Health Canada’s radon survey, the national burned-area record and the flood map inventory.
What Saint-Thomas faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Saint-Thomas grades B− for hazard risk
The grade weighs Saint-Thomas’ seismic risk and radon equally, and wildfire is one-sided: a high band counts against a town, a low one earns nothing.
Its place: #88 of 507 in Quebec and #1,639 of 2,589 Canadian towns.
How sure: The seismic figure is a long-run average from NRCan’s model, not a prediction. The radon share rests on 77 home tests in the survey area, so a few homes move it. The burned-area record misses fires under about 10 ha and most grass and farm fires.
Few fires near Saint-Thomas: 0% within 5 km, 0% within 25 km
Fires mapped since 1986 around where Saint-Thomas’ residents live, and the fuel next to their homes.
Next to the typical Canadian town (0.000% a year), Saint-Thomas’ 0.001% is in the low band.
5.3% of the land within 5 km of Saint-Thomas is forest fuel, close to the 7.8% 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 Quebec · highest of 513
Saint-Thomas burns at 0.001% a year, 136th of 513 towns in Quebec; the leader, Mistissini, reaches 0.31%.
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.
7.5% of Canada’s 2,610 towns burn fast enough to rank moderate or above; Saint-Thomas stays low, with 92%.
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.
MRC Joliette has mapped flooding for Saint-Thomas (1 study)
Flood studies whose area touches Saint-Thomas, from NRCan’s inventory, each linked to its owner.
MRC Joliette holds the flood mapping that covers Saint-Thomas (2016), linked below.
| Study | By | Year | Status |
|---|---|---|---|
| Joliette-Notre-Dame-des-Prairies-Notre-Dame-de-Lourdes-St-Paul-St-Thomas-St-Charles-Borromée | MRC Joliette | 2016 | final |
Towns with a flood study on file
Saint-Thomas is one of the 45% of towns in Quebec with a flood study on file, fewer than Canada’s 58%.
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 Saint-Thomas 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.”
Natural Resources Canada, Canada Flood Map Inventory; links go to each study’s owner.
Shaking is Saint-Thomas’ costliest hazard: $0.15 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.
At $0.15 per $1,000, Saint-Thomas carries roughly 4.9 times the typical Canadian town’s earthquake risk ($0.030).
Shaking damage a year per $1,000 of building value
Shaking damage around Saint-Thomas runs at $0.15 a year, near the $0.14 of the typical town in Quebec; La Pocatière has $0.48.
NRCan seismic risk model (2022): mean yearly building loss per $1,000 of value; medians of towns of 2,500 people or more.
More earthquake risk than most: only 19% of Canada’s 2,611 towns are above Saint-Thomas.
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 Saint-Thomas 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).
3.9% of homes tested around Saint-Thomas are over the radon guideline
Health Canada’s survey of long-term home tests: the share above the 200 Bq/m³ guideline. · Shared with the rest of the Lanaudiere health region: radon tests
At 3.9% over the guideline, the area around Saint-Thomas is under the typical Canadian town’s 6.6%.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Saint-Thomas’ area, at 3.9%, is below the median in Quebec (8.2%).
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 Saint-Thomas; 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.
Health Canada advises testing every home, Saint-Thomas’ included, whatever the area’s figure.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Where to get warnings in Saint-Thomas
Alerts for Saint-Thomas 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 Saint-Thomas 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 Saint-Thomas
The same four hazards for the places next door.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Saint-Thomas | Low | $0.15 | 3.9% | Yes |
| Joliette 22,408 · 7.2 km | Low | $0.17 | 3.9% | Yes |
| Saint-Paul 7,208 · 7.3 km | Low | $0.17 | 3.9% | Yes |
| Notre-Dame-des-Prairies 9,622 · 7.9 km | Low | $0.16 | 3.9% | Yes |
| Saint-Charles-Borromée 16,904 · 9.8 km | Low | $0.16 | 3.9% | Yes |
| Sainte-Élisabeth 1,473 · 11 km | Low | $0.14 | 3.9% | None listed |
| Lanoraie 5,694 · 11 km | Low | $0.13 | 3.9% | Yes |
Fire is no heavier anywhere nearby than around Saint-Thomas (low), with Joliette next at low.
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Saint-Thomas faces
What to do about the hazards Saint-Thomas 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.
- Drop, cover and hold on.
- Strap the water heater down.
- Keep 72 hours of supplies.
- Has it had a radon test?
- Check the address on the flood map.
- Are flood and wildfire insured?
- Is earthquake cover included?
What this data can and can’t tell you
- 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 Saint-Thomas.
- Flood studies aren’t flood zones. Flood studies cover areas of every size, which is why the page lists them for Saint-Thomas without grading them.
- 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 Saint-Thomas until then.
- Earthquakes are modelled. The earthquake figure is an expected loss, not a forecast, worked out by NRCan for each census subdivision, Saint-Thomas’ included.
Questions about flooding and hazards in Saint-Thomas
Is Saint-Thomas at risk of wildfire?
Less than most of Canada: 0% of the land within 25 km of Saint-Thomas has burned since 1986, the last in 2025, a low band that leaves Risk alone.
Does Saint-Thomas flood?
A flood study covers Saint-Thomas on Canada’s Flood Map Inventory; open the owner’s map to check a street, since flood isn’t graded.
How is Saint-Thomas’s Hazard risk Grade worked out?
Hazard risk gives Saint-Thomas B−, weighing earthquakes and radon and counting wildfire only against it.
Is radon a problem in Saint-Thomas?
In Health Canada’s survey, 3.9% of 77 homes tested in Saint-Thomas’ area were above 200 Bq/m³, though only a test tells you about one house.
How big is the earthquake risk in Saint-Thomas?
Expected earthquake damage in Saint-Thomas comes to $0.15 a year for each $1,000 that buildings are worth.
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).