Photo: Doug Hay derivative work: MrPanyGoff · CC BY 2.0Earthquake risk in Duncan runs 44 times the typical Canadian town’s: $1.33 per $1,000 a year
Fire seldom reaches Duncan: since 1986, 0.1% of the land within 25 km has burned (0.003% a year). In Health Canada’s survey, just 0.9% of homes tested in the area exceeded 200 Bq/m³ (6.6% typical). Hazard risk gives Duncan a grade of B−; its wildfire band pulls it down.
What stands out about Duncan’s hazards
Four national sources, each read for Duncan: earthquakes, radon, past fires and flood studies.
What Duncan faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Hazard risk in Duncan: B−
Risk averages earthquakes and radon; wildfire joins only where it pulls the average down, so a town like Duncan with little fire nearby would get no credit for it.
Its place: #169 of 254 in British Columbia and #1,710 of 2,589 Canadian towns.
How sure: The seismic figure is a long-run average from NRCan’s model, not a prediction. Small fires and grass fires are largely missing from the national burned-area record.
Wildfire is rare near Duncan: 0.1% of the land within 25 km burned since 1986, 0.1% within 5 km
Past fire around Duncan’s homes, from the national burned-area record, with the fuel within 5 km.
With 0.003% burned a year, Duncan is among the many low-band places (the typical Canadian town 0.000%).
The nearer ring around Duncan is less wooded (26% forest fuel) than the land out to 25 km (75%).
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 British Columbia · highest of 255
Duncan ranks 191st of the 255 towns in British Columbia for burn rate (0.003% a year), in the lower half; Oliver leads at 0.98%.
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.
The low band takes in 92% of Canada’s 2,610 towns, Duncan among them, though its rate is above zero; 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.
2 flood studies cover Duncan, the newest from Cowichan Valley Regional District
What Canada’s Flood Map Inventory lists for Duncan: who studied flooding and where to see their maps.
2 studies on the inventory touch Duncan, the newest Cowichan Valley Regional District’s from 2009, and their areas can be large, so they say maps exist, not that the town floods.
| Study | By | Year | Status |
|---|---|---|---|
| Lower Cowichan/Koksilah River Integrated Flood Management Plan | Cowichan Valley Regional District | 2009 | final |
| Cowichan and Koksilah Rivers at Duncan Floodplain Mapping | Ministry of Environment and Climate Change Strategy | 1997 | final |
Towns with a flood study on file
Its flood study puts Duncan with 76% of towns in British Columbia; 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.
No single decade dominates: 2 studies for Duncan between the 1990s and the 2000s.
Study dates as the NRCan inventory lists them, one count per study touching Duncan.
Listed, not scored: a flood study proves a map exists, not that Duncan floods.
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 Duncan’s costliest hazard: $1.33 a year per $1,000
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
At $1.33 per $1,000, Duncan carries roughly 44.4 times the typical Canadian town’s earthquake risk ($0.030).
Shaking damage a year per $1,000 of building value
Duncan has the highest shaking-damage figure in British Columbia, $1.33 a year per $1,000; the median is $0.36.
NRCan seismic risk model (2022): mean yearly building loss per $1,000 of value; medians of towns of 2,500 people or more.
Duncan is in the top tenth of Canada’s 2,611 towns for earthquake risk; 0% rank 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).
Roads, pipes and bridges aren’t in Duncan’s figure, nor landslides or tsunami: it is buildings and shaking.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
0.9% of homes tested around Duncan are over the radon guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
Duncan’s area, at 0.9%, is below the 6.6% of the typical Canadian town, though any one home can still be high.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Duncan’s area, at 0.9%, is below the median in British Columbia (1.8%).
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
Radon rarely tops the guideline around Duncan, as for 37% of Canada’s 2,611 towns; 63% see more.
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.
One home in Duncan can be high while next door is low; a three-month test settles it.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011). · Area behind the radon tests figures: the Central Vancouver Island health region
Weather and fire alerts for Duncan
Alerts for Duncan 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 Duncan 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)
How Duncan’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 |
|---|---|---|---|---|
| Duncan | Low | $1.33 | 0.9% | Yes |
| Electoral Area E, Cowichan Valley 4,482 · 1.5 km | Low | $0.83 | 0.9% | Yes |
| Cowichan 2,509 · 1.5 km | Low | $0.72 | 0.9% | Yes |
| North Cowichan 34,525 · 3.6 km | Low | $0.76 | 0.9% | Yes |
| Cowichan Bay 3,713 · 7.8 km | Low | $1.08 | 0.9% | Yes |
| Cobble Hill 5,074 · 13 km | Low | $0.68 | 0.9% | None listed |
| Shawnigan 9,903 · 15 km | Low | $0.57 | 0.9% | Yes |
Shawnigan burns a little more than Duncan, in the same low band (low here).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Duncan faces
What to do about the hazards Duncan 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
- Earthquakes are modelled. Shaking damage is modelled from the ground, the buildings and the odds of each quake, and published for whole subdivisions such as Duncan’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 Duncan until then.
- Flood studies aren’t flood zones. Flood studies cover areas of every size, which is why the page lists them for Duncan without grading them.
- Wildfire counts one way. The wildfire figure is the share of land within 25 km of Duncan’s homes burned each year from 1986 to 2025, past fire rather than a forecast, and it can only lower Risk.
Questions about flooding and hazards in Duncan
Does Duncan flood?
A flood study covers Duncan 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 Duncan?
In NRCan’s seismic model, Duncan’s buildings lose $1.33 per $1,000 of value in an average year.
Is Duncan at risk of wildfire?
Less than most of Canada: 0.1% of the land within 25 km of Duncan has burned since 1986, the last in 2022, a low band that leaves Risk alone.
How is Duncan’s Hazard risk Grade worked out?
Duncan grades B− for hazard risk, from earthquakes and radon, with wildfire counted only where it lowers the grade.
Is radon a problem in Duncan?
In Health Canada’s survey, 0.9% of 109 homes tested in Duncan’s area were above 200 Bq/m³, though only a test tells you about one house.
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).