Redding Fire Summit April 17 2019 1.Diablo winds - Climatology - Numerical simulations 2. Extreme Cases: Camp and Carr Fires
3. Extreme Fire in Canyons Fire-Atmosphere Coupling: Plume vs. Wind Driven
Analytical and Conceptual Framework
Byram (1954): Convective (Froude) Number 2 Fc < 1, fire is plume-driven and wind speed flow responds strongly to = buoyancy heat of fire 2 Fc > 1, fire becomes wind-driven and fire-atmosphere coupling decreases
No Wind / No Spread Wind-Driven Spread
Fire-Induced Flow Weak indrafts The Diablo Wind of Northern California: Climatology and Numerical Simulations
Coffee Park, Tubbs Fire Photo by Cal CHP Carrie Bowers (2018) Climatology Methods
Diablo Wind Criteria • Sustained winds 6 m s-1 or greater from NE • Persisting 6+ hours • Min RH ≤ 20% • 4+ stations impacted
17-year climatology • 42 NWS stations and RAWS initially • 18 stations with 14-17 yrs data and 2 or more events • Monthly avg live fuel moisture from 3 sites (old and new) Synoptic Composite • 43 events • 32 km NARR at closest hour to time of max wind speed Event Frequency
• 2.5 events/yr on average
• 6 events in 2014
• No recorded events in 2016
• October has highest frequency - minimum fuel moisture
• Very infrequent in summer Numerical Simulation of Diablo Winds during the Tubbs Fire
Hydraulic Jump Numerical Simulation of Diablo Wind Event during Tubbs Fire 2017-10-09 0300 PDT
Critical layer Winds lift from surface
• 3AM is time when fire spread stopped spreading at Coffee Park Rapid Onset of Downslope Wind Events
Surface weather conditions during Santa Ana wind, Oxnard Carr Fire Tornado (EF-3) Redding, California 26 July 2018
We really don’t understand the dynamics of how wildfires create their own weather, and what role this has on fire behavior. Carr Fire Analysis from Lareau et al. (2018)
HRRR Reanalysis Camp Fire: Observations of Doppler Lidar Winds
Mobile Profiling System
• Wind-driven fire • Smoke remains within 1-1.5 km AGL (8 Nov 2018) • Vertical profile indicates winds above the ground much stronger than at surface. Camp Fire: Meteorological Conditions and Fuels
• Critical FMC: 4-7%
• Strong downslope and gap winds
• Ambient RH = 14%
• Indices dominated by wind
NFDRS 2016 Dead Fuels Fire Behavior in Canyons Eruptive Fire Behavior Viegas (2005) proposed the term ‘fire eruption’ given the similarity between volcanic eruptions and wildfire as it accelerates. Also known as “blow-up” fire behavior. Fires on steep slopes and in canyons have behavior where ROS increases continuously—producing a fire eruption. Fire eruption in canyons is not rare! Fatalities from Wildfire in Canyons
Viegas and Simeoni (2010) Fire Behavior in Canyon Lab Experiments
Slide courtesy of Prof. D. X. Viegas, ADAI/CEIF Fire Behavior in Canyon Lab Experiments
Slide courtesy of Prof. D. X. Viegas, ADAI/CEIF Wind and Slope effects on Fire Behavior FIRETEC Simulations Pimont et al. (2012) (Low wind: 1 m/s) (High Wind: 10 m/s) narrow wide Extreme Fire Behavior in Canyons
Simulated area growth in a canyon fire for different canyon geometries using analytical model.
Forcing mechanisms
Enhanced convection and flame contact
Fire-Induced Flow
Slope limits entrainment
α Slope angle (Viegas and Pita 2004) A research-grade network of field sites for testing and evaluating wildfire science.
- New monitoring and sensor technologies for updating RAWS.
- Network covers a range of fuel and climatological conditions.
- Extensive fuels sampling (FMC).
- FWIs, FPI, NFDRS test sites Profiling Network for Extreme Fire Weather Monitoring
• Wind profiles up to 6 km (~ 3 miles)
• High-frequency: every 2 seconds
• Data integration into weather prediction models.
Doppler Lidar and Radars
Lidar/Radar Network Summary
Diablo Winds • Diablo winds are downslope winds that form in the lee of the Coastal Ranges.
• Frequency is 2.5 year-1 with a maximum frequency occurring in October when Live Fuel Moisture is at its lowest.
• Numerical simulations of the Tubb’s Fire indicate that the surface winds decreased due to flow detachment.
• Downslope winds associated with rapid onset and changes to surface conditions. Summary Cont.
California Wildfire Case Studies
• Carr Fire: an extreme event associated with ambient wind shear and critical 100-hr fuel moisture.
• Camp Fire: an extreme event associated with strong downslope winds and very dry air and critical fuel moisture.
• Rapid-response monitoring provides critical data for emergency response.
Wildfire in Canyons: “canyons are killers” • Fire spread in canyons is not steady state.
• Fire eruption associated with terrain and plume attachment.
• More research needed on topic (Spain 2022). Thank you!