Preparedness means practicing for the outliers and reducing vulnerabilities in advance, not just reacting after a once-in-a-generation storm. The July 1 event and others give concrete local examples to build on.
**The July 1, 2026 flooding (up to ~167 mm in a few hours in places like Britannia, city-labeled roughly a 1-in-200-year event in spots, thousands of basement floods, major insured losses concentrated in Nepean/southwest Ottawa as part of a broader Ontario-Quebec thunderstorm event later estimated around $491 million) is a clear real-world example of the “expect the unexpected” theme in my 2023 unpublished.ca piece.** It showed how intense short-duration rainfall can overwhelm drainage, cause widespread property damage, disrupt services, and leave people dealing with insurance gaps, cleanup, and long-term fallout (some apartment residents reported months of issues).
Drawing from recent years of news, official climate assessments (including Ottawa’s Climate Ready work and vulnerability studies), and events that have already hit the National Capital Region or nearby, here are other plausible high-impact scenarios that are possible even if not the most probable in any given year. These align with the piece’s call to imagine and prepare for outliers beyond routine asset-focused planning.
### Extreme convective storms, tornadoes, and derecho-style wind events
Ottawa has already seen these. The 2018 EF3 tornado path from Dunrobin into Gatineau caused major structural damage, power outages, and injuries. The May 2022 derecho brought estimated gusts up to ~190 km/h in parts of the city, widespread tree and infrastructure destruction, power outages affecting hundreds of thousands (Hydro Ottawa described some impacts as worse than the 1998 ice storm or 2018 tornadoes in scale), fatalities regionally, and roughly $1 billion in damages across Ontario and Quebec. Smaller tornadoes have occurred more recently (e.g., Barrhaven area in 2023; EF0 near Kemptville in August 2026). Climate projections and recent patterns support more favorable conditions for severe winds, tornadoes, and long-lived thunderstorm lines. A stronger or more urban-centered event, or a sequence of them, remains possible and could combine with flooding or power loss.
### Ice storms, freezing rain, and severe winter events
The 1998 ice storm remains a regional benchmark for prolonged outages and infrastructure damage. A late-March 2025 ice storm in Ontario and Quebec was one of the costliest events of that year for insurers (~$466 million). Projections note more days near 0°C and potential increases in freezing rain under climate change, with recent warnings (e.g., around El Niño influences) of more freeze-thaw cycles and ice accumulation. Extended outages in extreme cold (or followed by thaw/flooding) stress heating, water systems, and vulnerable populations. Record snowfalls have also disrupted the city in recent years.
### Prolonged or intense heat waves
Ottawa has experienced multi-day heat events with high humidex values (near or at records around 46–47). 2025 already featured multiple heat warnings and a high number of days over 30°C. Official projections point to roughly four times as many very hot days by the 2050s under higher-emission scenarios, plus more humidity. Impacts include health system strain (emergency visits, hospitalizations), power demand spikes that risk outages, and amplified effects on seniors, outdoor workers, and those without adequate cooling. Compounding with wildfire smoke or infrastructure issues raises the stakes.
### Major riverine flooding or compound flood events
2017 and 2019 Ottawa River floods caused extensive property damage, access issues, and stress on critical infrastructure (including the Britannia water purification plant, which has required sandbagging and contingency planning for access and operations). Climate trends favor heavier precipitation and more intense spring freshets. A flood exceeding recent peaks, or one coinciding with urban pluvial flooding like July 1, 2026, could threaten water treatment, transportation, and low-lying neighborhoods. Permanent flood defenses have been discussed for the plants.
### Wildfire smoke, drought-related fires, or a larger conflagration in the Gatineau/Ottawa Valley area
Distant wildfires have already pushed Ottawa’s Air Quality Health Index to extreme levels (2023, 2025). Locally, Gatineau Park and Ottawa Valley areas see periodic high or extreme fire danger, open-fire bans, and occasional small blazes. Dry spells combined with climate factors, pests (e.g., pine beetles), and abundant fuels make a larger, harder-to-control fire possible, with smoke, evacuation, and ecological impacts—even if current risk is often moderate-to-low. The 2022 derecho already showed how wind events can devastate tree cover and create more fuel.
### Water supply contamination or disruption (including nuclear-waste related concerns)
The ongoing Near Surface Disposal Facility (NSDF) project at Chalk River (Deep River area, upstream on the Ottawa River) for low-level radioactive waste has faced legal challenges from Algonquin First Nations, opposition from downstream municipalities (including concerns for Ottawa, Gatineau, and Montreal drinking water), and debate over design, leakage potential, seismic activity, and extreme weather resilience. Official assessments have found limited expected impact with mitigations, but the controversy highlights a low-probability, high-consequence risk to the river that supplies the city. Accidental releases, extreme flooding/erosion interacting with waste sites, or other contamination events remain in the “possible” category. Access or operational issues at Britannia or Lemieux plants during floods add another layer.
### Cascading or compound failures
Recent years show the risk of overlapping stresses: power outages during heat or ice events; multiple extremes in one season (2026’s record-wet summer with the July 1 deluge); infrastructure strain on the 417/Queensway (hazmat or multi-vehicle incidents during weather); or social/service disruptions amplifying natural events. The city’s own climate resiliency work identifies priorities around flooding, heat, severe winds, freezing rain, invasive species/pests, and service continuity, with notes on reduced response capacity during repeated or simultaneous events.
These are grounded in events that have already occurred or are flagged in local climate vulnerability work—not pure speculation. Many are becoming somewhat less “unexpected” as patterns shift, which strengthens the case for proactive practice, community-level mitigation, and imagining worst-case overlaps rather than relying solely on process and asset inventories. Nuclear detonation or exotic scenarios from the piece remain far lower probability but illustrate the same logic of thinking beyond the routine.
MY piece’s core point holds: preparedness means practicing for the outliers and reducing vulnerabilities in advance, not just reacting after a once-in-a-generation storm. The July 1 event and the others above give concrete local examples to build on.
i
Illustrative Risk Probabilities for Ottawa
2026–2030 Term of
Council
Estimated chance of at least one notable / impactful event during the four-year term. These are rough, qualitative judgments based on recent history, observed trends, and City of Ottawa / NCC climate projections — not formal actuarial or scientific forecasts.
| Risk | Estimated Probability (for 2026–2030) | Rationale / Recent Context |
|---|---|---|
| Intense short-duration rainfall / urban (pluvial)
flooding (July 1 2026 style) |
High 70–85% |
2026 already produced a near-record event; climate projections show increased extreme precipitation intensity. Multiple damaging urban floods possible. |
| Prolonged or
intense heat waves (multi-day, high humidex) |
Very
High 90%+ |
Multiple heat events already common. Projections indicate roughly 2–4× as many days >30 °C by the 2030s–2050s. Near-certain each summer. |
| Significant wildfire smoke
impacts (AQHI ≥7–10+ for multiple days) |
High 60–75% | Repeated heavy smoke episodes in 2023 and 2025. Large western and northern fire seasons remain likely under current climate trends. |
| Major ice storm / prolonged freezing rain | Moderate 35–50% |
1998 remains the benchmark; 2025 Ontario–Quebec ice storm was costly. More days near 0 °C increase the risk of freezing rain. |
| Severe convective storms / tornadoes / derecho-type winds | Moderate 25–40% |
2018 EF3 (Dunrobin–Gatineau), 2022 derecho (estimated 190 km/h gusts, massive outages), plus smaller recent tornadoes. Favourable conditions expected to persist or increase. |
| Major Ottawa River (riverine) flooding | Moderate 25–40% |
2017 and 2019 were significant. Heavier spring precipitation and freshets raise the chance of another large event, including potential impacts on water-treatment access. |
| Cascading infrastructure
failures (power + heat/cold/flood overlap) |
Moderate 30–45% |
Already observed when storms or ice coincide with extreme temperatures. Higher likelihood as individual extreme-event frequency rises. |
| Significant civil unrest / large-scale sustained protests | Low–Moderate 15–30% |
2022 trucker convoy demonstrated the possibility of multi-week disruption. Labour, housing, or political flashpoints remain possible but not the baseline expectation. |
| Local significant wildfire |
Low 10–20% |
Periodic high fire danger and small blazes occur; large, hard-to-control local fires remain uncommon but become more plausible in dry periods. |
| Major water-supply contamination
event (including nuclear-waste-related scenarios at Chalk River) |
Very Low <5% |
Ongoing controversy and residual risk around the Near Surface Disposal Facility and historical waste. Designed and regulated to very low probability of significant release affecting Ottawa’s drinking water. |
