Photo: Raysonho @ Open Grid Scheduler / Grid Engine · CC0Markham is on Canada’s flood inventory: 3 listed, led by Toronto Regional Conservation Authority
No wildfire is mapped within 25 km of Markham’s homes since 1986 (0% of the land, 0.000% a year). Seismic risk in Markham sits near the middle: $0.034 of expected damage per $1,000 of buildings a year, the typical town $0.030. In Health Canada’s survey, just 0% of homes tested in the area exceeded 200 Bq/m³ (6.6% typical).
What stands out about Markham’s hazards
For Markham, from NRCan’s seismic model, Health Canada’s radon survey, the national burned-area record and the flood map inventory.
What Markham faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Markham isn’t graded for hazard risk yet
Seismic risk and radon set Markham’s grade, wildfire can drag it down, and flood mapping stays out of it.
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.
Little of the land around Markham has burned: 0% within 5 km, 0% within 25 km since 1986
Fires mapped since 1986 around where Markham’s residents live, and the fuel next to their homes.
Next to the typical Canadian town (0.000% a year), Markham’s 0.000% is in the low band.
Fire has stayed at least 5.4 km from Markham’s homes since 1986.
The forest starts beyond town: 2.2% of the land within 5 km of Markham’s homes is forest fuel, against 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 Ontario · highest of 872
Among the 872 towns in Ontario, Sioux Lookout burns fastest (0.16% a year); Markham is with the 639 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.
Markham shares the low band with 92% of Canada’s 2,610 towns, its burn rate rounding to nothing; 7.5% burn faster.
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.
Flooding around Markham is mapped in 3 studies, the newest by Toronto Regional Conservation Authority
Flood studies whose area touches Markham, from NRCan’s inventory, each linked to its owner.
For Markham the inventory points to 3 studies, most recently Toronto Regional Conservation Authority’s in 2021.
| Study | By | Year | Status |
|---|---|---|---|
| Toronto Floodline Consolidation | Toronto Regional Conservation Authority | 2021 | final |
| Duffins Creek | Toronto and Region Conservation Authority | 2020 | final |
| Unionville Special Policy Area | Toronto and Region Conservation Authority | 2019 | final |
Towns with a flood study on file
69% of towns in Ontario have a flood study, more than Canada’s 58%; Markham has one too.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Mapping around Markham goes back to the 2010s and peaks in the 2020s, with 2 of its 3 studies.
Study dates as the NRCan inventory lists them, one count per study touching Markham.
The grade leaves flood out, since a study area says nothing about how many of Markham’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 Markham: $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.
With $0.034 of shaking damage a year per $1,000, Markham is about even with the 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; Markham 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.
Markham sits mid-range among Canada’s 2,611 towns: 46% 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).
Only shaking damage to buildings in Markham 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).
Radon runs low around Markham: 0% of tested homes over the guideline
Health Canada’s survey of long-term home tests: the share above the 200 Bq/m³ guideline. · Radon tests for the York Regional Health Unit
Markham’s survey area reads 0% over the guideline, under the typical Canadian town’s 6.6%.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Fewer homes top the guideline around Markham (0%) than in the typical town in Ontario (4%).
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
Few tests over the guideline: Markham 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.
Radon varies from house to house in Markham, so the survey is a reason to test, not a result for yours.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Where to get warnings in Markham
Environment and Climate Change Canada issues the weather alerts for Markham; 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 Markham 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 Markham’s neighbours compare on hazards
The same four hazards for the places next door.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Markham | Low | $0.034 | 0% | Yes |
| Unionville 17,632 · 1.5 km | Low | $0.034 | 0% | Yes |
| Hagerman's Corners 43,555 · 2.1 km | Low | $0.034 | 0% | Yes |
| Quantztown 13,146 · 2.1 km | Low | $0.034 | 0% | Yes |
| Berczy Village 22,149 · 3.2 km | Low | $0.034 | 0% | Yes |
| Underwood 5,972 · 3.3 km | Low | $0.034 | 0% | None listed |
| Brown's Corners 7,228 · 3.3 km | Low | $0.034 | 0% | Yes |
The fire record around Unionville is a touch heavier than Markham’s, but the band is the same: low (here low).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Markham faces
Practical steps for Markham’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?
- 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. Health Canada’s survey tested some 14,000 homes over three months; until postal-area boundaries are loaded, Markham takes its 2007 health region’s share.
- Earthquakes are modelled. The earthquake figure is an expected loss, not a forecast, worked out by NRCan for each census subdivision, Markham’s included.
- 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 Markham.
- Flood studies aren’t flood zones. The flood inventory points to maps; it is incomplete and not the official source, so ask the municipality about any street in Markham.
Questions about flooding and hazards in Markham
Is Markham at risk of wildfire?
Some, but Markham’s low band (0% of nearby land burned since 1986, latest 2001) is short of the level that counts.
Is radon a problem in Markham?
The area’s survey found 0% of 95 tested homes above Health Canada’s guideline, so a three-month test is worth doing in Markham.
How is Markham’s Hazard risk Grade worked out?
Not yet: Canada’s grades come with its first grading run, when Risk will weigh earthquakes and radon in Markham, with wildfire able only to lower it.
Does Markham flood?
The inventory lists a study touching Markham; whether a given street floods is on that map, not in the grade.
How big is the earthquake risk in Markham?
Expected earthquake damage in Markham comes to $0.034 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).