Photo: Canmenwalker · CC BY 4.0Mount Dennis is on Canada’s flood inventory: 2 listed, led by Toronto Regional Conservation Authority
Wildfire barely registers for Mount Dennis, at 0% of the land within 25 km since 1986 (0.000% a year). Seismic risk in Mount Dennis sits near the middle: $0.043 of expected damage per $1,000 of buildings a year, the typical town $0.030. In Health Canada’s survey, just 2.7% of homes tested in the area exceeded 200 Bq/m³ (6.6% typical). Hazard risk gives Mount Dennis a grade of A−, from earthquakes and radon alone.
What stands out about Mount Dennis’s hazards
For Mount Dennis, from NRCan’s seismic model, Health Canada’s radon survey, the national burned-area record and the flood map inventory.
What Mount Dennis faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Mount Dennis grades A− for hazard risk
For Mount Dennis, Risk will be the average of earthquakes and radon, with wildfire added only if it makes the average worse.
Its place: #285 of 866 in Ontario and #700 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 74 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.
Wildfire is rare near Mount Dennis: 0% of the land within 25 km burned since 1986, 0% within 5 km
Fires mapped since 1986 around where Mount Dennis’ residents live, and the fuel next to their homes.
In a typical year 0.000% of the land near Mount Dennis burns; the typical Canadian town sees 0.000%, and both are low.
Land that isn’t forest covers nearly all the ground around Mount Dennis: forest fuel is 0.5% within 5 km and 0.8% 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 Ontario · highest of 871
Among the 871 towns in Ontario, Sioux Lookout burns fastest (0.16% a year); Mount Dennis 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.
Only 7.5% of Canada’s 2,610 towns are above the low band, which holds 92%; Mount Dennis, at a rounded zero, is far from them.
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.
Mount Dennis is on the flood map inventory: 2 studies, latest by Toronto Regional Conservation Authority
Flood studies whose area touches Mount Dennis, from NRCan’s inventory, each linked to its owner.
For Mount Dennis the inventory points to 2 studies, most recently Toronto Regional Conservation Authority’s in 2021.
| Study | By | Year | Status |
|---|---|---|---|
| Toronto Floodline Consolidation | Toronto Regional Conservation Authority | 2021 | final |
| Rockcliffe Special Policy Area | Toronto and Region Conservation Authority | 2020 | final |
Towns with a flood study on file
Its flood study puts Mount Dennis with 69% of towns in Ontario; Canada’s share is 58%.
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 Mount Dennis.
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 Mount Dennis: $0.043 per $1,000 of buildings a year
NRCan’s seismic risk model: the damage shaking is expected to do to buildings each year, on average over many years.
At $0.043 per $1,000, Mount Dennis’ earthquake risk is about the typical Canadian town’s ($0.030; 1.4 times).
Shaking damage a year per $1,000 of building value
Shaking damage around Mount Dennis runs at $0.043 a year, near the $0.043 of the typical town in Ontario; 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.
Mount Dennis’ earthquake risk lands near the centre of Canada’s range; 36% 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).
For Mount Dennis the model prices shaking damage to buildings, nothing more.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean). · Not measured by town: earthquake risk (the city of Toronto)
Little radon around Mount Dennis: 2.7% of area homes over the guideline
Health Canada’s survey of long-term home tests: the share above the 200 Bq/m³ guideline. · Area-wide: radon tests, counted over the City of Toronto Health Unit
At 2.7% over the guideline, the area around Mount Dennis is under the typical Canadian town’s 6.6%.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Against the typical town in Ontario (4%), the area around Mount Dennis has fewer high tests: 2.7%.
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 Mount Dennis’ 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.
Whatever Mount Dennis’ 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).
Where to get warnings in Mount Dennis
Environment and Climate Change Canada issues the weather alerts for Mount Dennis; 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. |
For fires near Mount Dennis, the national fire information system maps danger and active fires daily; local authorities give any evacuation order.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
Hazards in the places around Mount Dennis
The same four hazards for the places next door.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Mount Dennis | Low | $0.043 | 2.7% | Yes |
| Rockcliffe-Smythe 22,242 · 1.3 km | Low | $0.043 | 2.7% | Yes |
| Brookhaven-Amesbury 17,541 · 1.5 km | Low | $0.043 | 2.7% | Yes |
| Humber Heights-Westmount 10,427 · 2.1 km | Low | $0.043 | 2.7% | Yes |
| Beechborough-Greenbrook 6,419 · 2.1 km | Low | $0.043 | 2.7% | Yes |
| Weston 18,896 · 2.3 km | Low | $0.043 | 2.7% | Yes |
| Keelesdale-Eglinton West 11,407 · 2.3 km | Low | $0.043 | 2.7% | Yes |
None of the places around has more fire nearby than Mount Dennis (low); Rockcliffe-Smythe comes closest (low).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Mount Dennis faces
Practical steps for Mount Dennis’ 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
- Earthquakes are modelled. Seismic risk is NRCan’s model of yearly building losses from shaking, averaged over many years and given for Mount Dennis’ census subdivision (a neighbourhood shows its city’s).
- 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 Mount Dennis until then.
- Flood studies aren’t flood zones. Flood studies cover areas of every size, which is why the page lists them for Mount Dennis without grading them.
- Wildfire counts one way. For Mount Dennis, 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 Mount Dennis
How is Mount Dennis’s Hazard risk Grade worked out?
Hazard risk gives Mount Dennis A−, weighing earthquakes and radon and counting wildfire only against it.
Is radon a problem in Mount Dennis?
The area’s survey found 2.7% of 74 tested homes above Health Canada’s guideline, so a three-month test is worth doing in Mount Dennis.
Is Mount Dennis at risk of wildfire?
The burned-area record shows next to nothing around Mount Dennis (0% within 25 km since 1986), so its band is low.
Does Mount Dennis flood?
A flood study covers Mount Dennis on Canada’s Flood Map Inventory; open the owner’s map to check a street, since flood isn’t graded.
How big is the earthquake risk in Mount Dennis?
About $0.043 a year per $1,000 of building value, NRCan’s long-run expectation for Mount Dennis.
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).