CSquared Prairie Fire Risk Indicator Technical Justification – Phase 1 Model
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, and humidity below ~30% rapidly dries grass fuels. Because of this, wind thresholds are the most critical trigger.
Historical prairie grass fires show rapid spread begins around 25–30 km/h, fire control difficulty increases significantly above 35 km/h, and extreme spread occurs above 40 km/h sustained wind. Relative humidity also strongly influences ignition probability: RH above 30% reduces ignition probability, while RH below 25% significantly increases fire intensity.
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 30–50 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 weather station) and forecast conditions (Environment Canada hourly forecast). 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 Conditions: Safe burning practices generally acceptable. Level 2 — Fire Advisory: Reduce ignition sources. Level 3 — Fire Restriction (Recommended): Suspend debris burning and minimize open flame. Level 4 — Fire Ban Conditions (Recommended): Avoid all ignition sources during extreme wind and drought.
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 Environment Canada 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. Below 20 km/h, fires spread slowly and are usually controllable. At 25–30 km/h, grass fires begin spreading rapidly. At 30–35 km/h, fire control becomes difficult. Above 35 km/h, rapid fire runs are likely. Above 40 km/h, extreme spread is possible. US Forest Service Stage 1 restrictions are often implemented when winds exceed ~25 mph (~40 km/h), and Australian grass fire warnings escalate above ~30 km/h.
Relative Humidity Thresholds
Above 30% RH, ignition probability is lower. At 25–30%, ignition potential is elevated. Below 25%, rapid fire growth is possible. Below 20%, extreme fire behavior is possible. These ranges appear in both the U.S. NFDRS and Canadian FWI components.
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 7 days partially moderates fuels. Less than 5 mm in 7 days indicates drying fuels. Minimal rain over 7–14 days results in cured grass fuels. Minimal rain over 14+ days indicates high drought stress.
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 consistent with wildfire operational practices used internationally. 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.