CSquared Prairie Fire Risk Indicator
Technical Justification — Phase 1 Model
c2sk.ca — Silton, Saskatchewan
Purpose
The CSquared Prairie Fire Risk Indicator is a simplified public-information model designed to communicate wildfire ignition risk for the Silton / Saskatchewan Beach area. It converts complex wildfire danger factors into four clear public guidance levels. The system is informational only and does not replace municipal bylaws or provincial restrictions.
Design Principles
The model is based on operational wildfire practices used by agencies including the United States Forest Service (USFS), Bureau of Land Management (BLM), Country Fire Authority (Australia), New South Wales Rural Fire Service, and the Canadian Forest Fire Danger Rating System (CFFDRS). These agencies consistently emphasize three dominant wildfire drivers: wind speed, relative humidity, and fuel dryness (drought conditions). Temperature is considered a secondary factor because wind and humidity are the primary drivers of fire spread in grassland environments.
Prairie Fire Behavior Considerations
The Saskatchewan prairie environment behaves differently from forest wildfire systems:
- Grass fuels ignite easily when cured; fire spread is primarily wind-driven
- Large fire runs often occur on moderate temperature days with strong wind
- Humidity below approximately 30% rapidly dries grass fuels
- Wind thresholds are the most critical trigger in this environment
Historical prairie grass fire data shows rapid spread can begin at wind speeds as low as 15–20 km/h when combined with low humidity and dry fuel conditions. Fire control difficulty increases significantly as wind approaches 25 km/h and above.
Why Temperature Was Reduced as a Primary Trigger
Prairie wildfire events frequently occur under moderate temperatures when wind is high. Typical prairie fire days often have temperatures of 18–28°C, wind of 25–50 km/h, and RH of 20–35%. If temperature thresholds were required, many high-risk fire days would be incorrectly classified as low risk. For this reason temperature is treated only as a supporting drying indicator, not a primary trigger.
Forecast Integration
Unlike many public fire advisory systems, this model considers both observed conditions (local Ambient Weather station) and forecast conditions (hourly forecast via Open-Meteo). The published level equals the highest of the observed level or the forecast level over the next 24 hours. This approach mirrors operational wildfire agencies which frequently implement restrictions based on forecast wind events before they occur.
Four-Level Public Model
Level 1 — Normal:
Safe burning practices generally acceptable. No significant fire weather concerns.
Level 2 — Medium:
Conditions becoming risky. Reduce ignition sources and avoid debris burning.
Level 3 — High:
Rapid grass fire spread possible. Suspend debris burning and minimize open flame.
Level 4 — Extreme:
Avoid all ignition sources. No open flame or hot works (welding, cutting, grinding) during extreme wind and drought conditions.
Why a Recommendation Model Was Chosen
The CSquared system is designed as public guidance only — to avoid conflict with municipal authority, allow flexibility across multiple RMs and villages, and encourage voluntary risk reduction. If successful, the model could later inform formal fire restriction decisions by local authorities.
Conclusion
The CSquared Prairie Fire Risk Indicator provides a simplified, locally informed method to communicate wildfire ignition risk in prairie environments. By combining real-time weather station data with Open-Meteo forecasts, it provides early warning of wind-driven fire conditions common in southern Saskatchewan. The system prioritizes clarity, transparency, and practical public guidance while remaining consistent with wildfire risk frameworks used internationally.
Appendix A — Trigger Threshold Justification
Primary Fire Spread Drivers
Wildfire agencies consistently identify three dominant variables controlling grass fire behavior: wind speed, relative humidity, and fuel dryness (recent rainfall / drought). These variables appear in the US National Fire Danger Rating System (NFDRS), Canadian Forest Fire Danger Rating System (CFFDRS), and Australian Fire Danger Index (FDI). Temperature is included in those systems but primarily affects fuel drying rather than immediate spread rate.
Wind Thresholds
Wind speed is the single most important factor in prairie fire spread. The system uses lower wind thresholds than some forest-oriented frameworks because prairie grass fuels are more responsive to wind at lower speeds:
- Below 15 km/h: fires spread slowly and are usually controllable — Level 1 (Normal)
- At 15–19 km/h with low RH and dry fuels: ignition potential is elevated — Level 2 (Medium) may apply
- At 20–24 km/h with low RH and extended dry period: fire control becomes difficult — Level 3 (High) may apply
- At ≥25 km/h sustained or gusts ≥35 km/h under drought conditions: rapid fire runs are likely — Level 4 (Extreme) may apply
Relative Humidity Thresholds
Relative humidity directly controls fuel moisture and ignition probability:
- Above 40% RH: ignition probability is lower and fire spread is limited — Level 2 (Medium) does not trigger
- At 30–39% RH with elevated wind: ignition potential rises — Level 2 (Medium) conditions may apply
- Below 30% RH with ≥20 km/h wind and dry days: rapid fire growth possible — Level 3 (High) conditions apply
- Below 25% RH with ≥25 km/h wind and extended drought: extreme fire behavior possible — Level 4 (Extreme) conditions apply
These ranges are consistent with both the U.S. NFDRS and Canadian FWI components, adjusted downward for prairie grass fuels which respond faster than timber fuels.
Rainfall / Drought Indicators
Fuel dryness is approximated using recent rainfall totals as a practical proxy for complex fuel moisture calculations:
- Rain greater than 5 mm in the past 7 days partially moderates fuels and prevents Level 2 (Medium) from triggering
- Less than 5 mm in 7 days indicates drying fuels
- Seven or more consecutive dry days (less than 0.5 mm/day) combined with ≥20 km/h wind and RH below 30% triggers Level 3 (High)
- Fourteen or more consecutive dry days under the same wind and RH conditions triggers Level 4 (Extreme)
Trigger Thresholds Summary
All conditions within a level must be met (AND logic), except Level 4 wind/gust which is OR.
| Level | Label | Wind | Gusts | RH | Dry Days | Rain (7-day) |
|---|---|---|---|---|---|---|
| 1 | Normal | — | — | — | — | — |
| 2 | Medium | ≥ 15 km/h | — | < 40% | — | < 5 mm |
| 3 | High | ≥ 20 km/h | — | < 30% | ≥ 7 days | — |
| 4 | Extreme | ≥ 25 km/h | ≥ 35 km/h (OR) | < 25% | ≥ 14 days | — |
Forecast Integration
Wildfire agencies commonly implement restrictions before critical weather arrives — USFS and BLM issue fire restrictions prior to forecast wind events, and Australian Total Fire Ban declarations are based on predicted Fire Danger Index. For this reason the CSquared model publishes the highest of observed or forecast conditions over the next 24 hours.
Conclusion
The thresholds used in the CSquared Prairie Fire Risk Indicator are calibrated for prairie grass fuel conditions in southern Saskatchewan, where fire spread can begin at lower wind speeds than forest environments. The model simplifies complex fire danger systems while retaining the key environmental drivers responsible for prairie wildfire ignition and spread, allowing clear public communication while maintaining transparency in how risk levels are determined.
Risk model informed by wildfire restriction frameworks used by the United States Forest Service, Bureau of Land Management, and Australian Country Fire Authority.