Photo: P199 · CC BY-SA 3.0Hazard risk in Dorchester is lower than in 90% of Canadian towns
Since 1986 almost nothing has burned near Dorchester: 0% of the land within 25 km, or 0.000% a year. NRCan expects $0.020 of shaking damage a year per $1,000 of buildings in Dorchester, near the typical $0.030. Radon is lower than usual: 1.8% of tested homes in the survey area topped the guideline, against 6.6% for the typical town. Dorchester grades A for hazard risk; wildfire is low here, so it earns no credit.
What stands out about Dorchester’s hazards
Four national sources, each read for Dorchester: earthquakes, radon, past fires and flood studies.
What Dorchester faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Hazard risk in Dorchester: A
Seismic risk and radon set Dorchester’s grade, wildfire can drag it down, and flood mapping stays out of it.
Its place: #43 of 866 in Ontario and #347 of 2,589 Canadian towns.
How sure: Earthquake losses are a model’s expectation over many years, not a forecast for any one. Small fires and grass fires are largely missing from the national burned-area record.
Little of the land around Dorchester has burned: 0% within 5 km, 0% within 25 km since 1986
Past fire around Dorchester’s homes, from the national burned-area record, with the fuel within 5 km.
The yearly burn rate around Dorchester is 0.000%, low beside 0.000% for the typical Canadian town.
Only 0.7% of the land within 25 km of Dorchester is forest fuel, and 0.6% close in.
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
Of the 871 towns in Ontario, 638 have a burn rate that rounds to zero, Dorchester among them; Sioux Lookout leads at 0.16% a year.
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.
Measured against 2,610 towns, Dorchester is in the largest group, low (92%), and at its floor, while 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 Dorchester
What Canada’s Flood Map Inventory lists for Dorchester: who studied flooding and where to see their maps.
An empty entry for Dorchester on the inventory isn’t proof of safety; ask locally for flood maps.
Towns with a flood study on file
Flood maps are common in Ontario, 69% of towns against 58% nationally, but none in the inventory touches Dorchester.
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 Dorchester 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.”
Earthquakes cost buildings in Dorchester $0.020 per $1,000 a year
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
At $0.020 per $1,000, Dorchester’s earthquake risk is about the typical Canadian town’s ($0.030; 0.7 times).
Shaking damage a year per $1,000 of building value
At $0.020, Dorchester 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.
Dorchester sits mid-range among Canada’s 2,611 towns: 64% expect more shaking damage.
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).
The loss is to Dorchester’s buildings alone, from ground shaking; infrastructure and secondary hazards are left out.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
1.8% of homes tested around Dorchester are over the radon guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
A lower share than most: 1.8% of tested homes around Dorchester, the typical Canadian town 6.6%.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Against the typical town in Ontario (4%), the area around Dorchester has fewer high tests: 1.8%.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
Few tests over the guideline: Dorchester shares the bottom band with 37% of Canada’s 2,611 towns, below the other 63%.
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.
Basements, soil and how a house is sealed decide its radon, so in Dorchester only a test can say.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011). · Radon tests: one figure for all of the Middlesex-London Health Unit
Weather and fire alerts for Dorchester
Alerts for Dorchester 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. |
Evacuation orders for Dorchester come from the municipality or the province, while CWFIS maps fire danger every day.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
Hazards in the places around Dorchester
Wildfire band, earthquake risk, radon and flood studies for each place nearby.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Dorchester | Low | $0.020 | 1.8% | None listed |
| Argyle 28,109 · 8.5 km | Low | $0.020 | 1.8% | None listed |
| Jackson 8,124 · 11 km | Low | $0.020 | 1.8% | None listed |
| Hamilton Road 15,283 · 11 km | Low | $0.020 | 1.8% | None listed |
| Huron Heights 20,890 · 12 km | Low | $0.020 | 1.8% | None listed |
| East London 10,972 · 12 km | Low | $0.020 | 1.8% | None listed |
| Glen Cairn 16,119 · 13 km | Low | $0.020 | 1.8% | None listed |
Dorchester’s low band tops its neighbours; Argyle is next (low).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Dorchester faces
Practical steps for Dorchester’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. About 14,000 homes were tested across Canada in 2009–2011, and the share over the guideline for Dorchester is its health region’s, the survey’s design unit.
- Earthquakes are modelled. NRCan models what earthquakes would cost buildings each year on average, subdivision by subdivision; Dorchester’s figure is its subdivision’s.
- 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 Dorchester.
- Wildfire counts one way. Wildfire is read from the national burned-area record around Dorchester’s homes since 1986, a history of fire that may lower Risk but never raises it.
Questions about flooding and hazards in Dorchester
How is Dorchester’s Hazard risk Grade worked out?
Dorchester grades A for hazard risk, from earthquakes and radon, with wildfire counted only where it lowers the grade.
Does Dorchester flood?
No study on Canada’s Flood Map Inventory covers Dorchester (0), which doesn’t mean it has never been mapped, so ask the municipality.
Is radon a problem in Dorchester?
1.8% of the 110 homes Health Canada tested around Dorchester topped the guideline; your own house needs its own test.
How big is the earthquake risk in Dorchester?
In NRCan’s seismic model, Dorchester’s buildings lose $0.020 per $1,000 of value in an average year.
Is Dorchester at risk of wildfire?
The burned-area record shows next to nothing around Dorchester (0% within 25 km since 1986), so its band is low.
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).