Fire/atmosphere interactions

1. Towards more accurate predictions of wildfire behavior Modeling surface/atmosphere interactions Mélanie ROCHOUX, Ph.D. Postdoctoral fellow Meteorological Research Division Introductory seminar 13 June 2014 Environnement Canada Environment Canada

2. ①➀ INTRODUCTION: Regional-scale modeling viewpoint • Fire danger • Multi-physics multi-scale problem • Regional-scale modeling viewpoint ➁ Ph.D. RESEARCH: How to address modeling uncertainties? • Data assimilation at regional scale • Multi-physics simulation at flame scale ➂ STATE-OF-THE-ART: Fire/atmosphere coupling • Coupling strategy • Atmospheric emissions • Offline simulation case OUTLINE Introductory seminar 2 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX

3. INTRODUCTION ● ● ● Fire danger at operational level • Global viewpoint: about 400 million hectares burnt every year ➙3 % of the Earth’s vegetation area © NASA Active fire map by MODIS over a 10-day period 9-18 August 2013 • Canadian Forest Fire Weather Index System • Fire Weather Index (FWI) ➙ numerical rating of fire potential intensity • Daily maps of fire weather • Main limitation ➙ meteorological index Canadian Wildland Fire Information System, NRCan INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX ➙ modis-fire.umd.edu/ 3

4. INTRODUCTION ● ● ● Fire danger at operational level Fine fuel moisture code (FFMC) Duff moisture code (DMC) Drought Code (DC) FUEL MOISTURE CODES FIRE WEATHER OBSERVATION S FIRE BEHAVIOR INDICES Air temperature and humidity, wind, 24-h rainfall Wind Air temperature and humidity, 24- h rainfall Air temperature, 24-h rainfall Initial spread index (ISI) Buildup index (BUI) Fire weather index (FWI) 4 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX • Canadian Forest Fire Weather Index System • Fire Weather Index (FWI) ➙ numerical rating of fire potential intensity • Daily maps of fire weather • Main limitation ➙ meteorological index ➙ cwfis.cfs.nrcan.gc.ca/home

5. INTRODUCTION ● ● ● Fire danger at operational level Fine fuel moisture code (FFMC) Duff moisture code (DMC) Drought Code (DC) FUEL MOISTURE CODES FIRE WEATHER OBSERVATION S FIRE BEHAVIOR INDICES Air temperature and humidity, wind, 24-h rainfall Wind Air temperature and humidity, 24- h rainfall Air temperature, 24-h rainfall Initial spread index (ISI) Buildup index (BUI) Fire weather index (FWI) 5 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX • Canadian Forest Fire Weather Index System • Fire Weather Index (FWI) ➙ numerical rating of fire potential intensity • Daily maps of fire weather • Main limitation ➙ meteorological index DMC: loosely compacted decomposing matter -nominal depth 7 cm DC: deep compact organic matter -nominal depth 18 cm FFMC: litter and other fine fuels -nominal depth 1.2 cm From Chelene Krezek-Hanes, Great Lakes Forestry Centre, Canadian Forest Service ➙ cwfis.cfs.nrcan.gc.ca/home

6. INTRODUCTION ● ● ● Multi-physics multi-scale problem 2009 Black Saturday bushfires ▶ 450 000 ha (1/3 of the annual burnt area in Australia) ▶ 173 people died ▶ strong fire/atmosphere coupling 300 km © NASA Fire/Surface ➙ Vegetation ➙ Topography Fire/Atmosphere ➙ Dynamics ➙ Chemistry Turbulence Gases & Aerosols Wind Biomass combustion Surface- to-canopy • Complexity of wildfire behavior • Wide range of length-scale (from mm to km) • Poorly-defined biomass fuels • Atmospheric external forcing • Climate change (megafires) ➙ CHALLENGE: How to accurately represent surface/atmosphere interactions in wildfires? 6 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX

7. INTRODUCTION ● ● ● Multi-physics multi-scale problem • Complexity of wildfire behavior • Wide range of length-scale (from mm to km) • Poorly-defined biomass fuels • Atmospheric external forcing • Climate change (megafires) ➙ CHALLENGE: How to accurately represent surface/atmosphere interactions in wildfires? Radiation Wind Flame Pyrolysis Heat/mass fluxes Terrain topography EMISSIONS PYROLYSI S COMBUSTION FLUID DYNAMICS HEAT TRANSFER ATMOSPHERIC PHYSICS 7 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX

8. INTRODUCTION ● ● ● Regional-scale modeling viewpoint © FOREFIRE, Favone wildfire (30 ha)© FOREFIRE, Favone wildfire (30 ha) Regional-scale viewpoint FIRE FRONT Burnt area Fire front Unburnt vegetation TOPOGRA PHY Terrain slope BIOMASS FUEL Moisture content Packing ratio Layer thickness WEATHER Wind magnitude Wind direction Rate Of spread • Front-tracking simulator • Prediction of the location of the surface fire front on horizontal plane • Local evaluation of the ROS along the normal direction to the fire front ➙ ROTHERMEL [1] ➙ BALBI [2] • Examples of simulator ➙ FOREFIRE [3], asynchronous Lagrangian solver ➙ FIREFLY [4], level-set solver [1] Rothermel, USDA Forest Service (1972) [2] Balbi et al. Comb. Flame (2004) [3] Filippi et al. Proc. Comb. Inst. (2013) [4] Rochoux, Ph.D. Ecole Centrale Paris (2014) 8 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX

10. PH.D. RESEARCH ● ● ● Modeling limitations INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX • ISSUE: How to accurately describe wildfire spread? 10 Rochoux M.C., Ph.D. Ecole Centrale Paris (2014) • OBJECTIVE: Quantify and reduce uncertainty in ROS modeling Data assimilation for REGIONAL-SCALE wildfire spread forecast Environmental conditions Fire front locationPhysics-based modeling FLAME-SCALE multi-physics CFD simulations

11. PH.D. RESEARCH ● ● ● Data assimilation for regional-scale forecast INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX 11 Environmental conditions Fire front location • Anisotropy in wildfire spread ➙ complex spatial correlations along the fireline • Highly non-linear observation operator ➙ complex relationship between ROS model parameters and model counterparts of observations Simulated front Observed front (x1 , y1 ) (x2 , y2 ) (x3 ,y3 ) (x4 , y4 ) (x1 O ,y1 O ) (x2 O ,y2 O ) Distance between fronts FIREFLY wildfire spread simulator Parameters Initial condition Boundary conditions Comparison Simulated fronts Observations

12. PH.D. RESEARCH ● ● ● Data assimilation for regional-scale forecast INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX 12 Environmental conditions Fire front location • Parameter estimation ➙ temporal variability of the errors in the ROS model parameters (mid- to long-term) ➙ reduced-cost approach (Polynomial Chaos) • State estimation ➙ persistence of the correction of the model initial condition (short-term) Simulated front Observed front (x1 , y1 ) (x2 , y2 ) (x3 ,y3 ) (x4 , y4 ) (x1 O ,y1 O ) (x2 O ,y2 O ) FIREFLY wildfire spread simulator Parameters Initial condition Boundary conditions Comparison Simulated fronts Observations Ensemble Kalman filter Parameter estimation State estimation Analysis

13. PH.D. RESEARCH ● ● ● Data assimilation for regional-scale forecast INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX 13 EnKF analysis of synthetic observations + of fire front FORECAST True location Ensemble members ANALYSIS True location Ensemble members observations Ensemble generation for state estimation ➙ Anisotropy in wildfire spread ➙ Selection of spatially-distributed biomass fuel properties and distinct wind conditions between the ensemble members. Approach relevant for incomplete observations due to: ➙ opacity of the thermal plume ➙ limited monitoring

14. PH.D. RESEARCH ● ● ● Data assimilation for regional-scale forecast INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX 14 Controlled grassland fire experiment x [m] y [m] Extraction of the 600 K iso-temperature at 14-s time intervals 1min32s50s 1min46s1min04s 1min28s Time FRONT Wind 1m/s

15. PH.D. RESEARCH ● ● ● Data assimilation for regional-scale forecast INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX 15 Controlled grassland fire experiment state parameter state parameter state parameter • STATE ESTIMATION: non-uniform correction of the fire front • PARAMETER ESTIMATION: mean correction along the fireline ANALYSIS PERFORMANCE ANALYSIS FORECAST

17. ➙ anridea.univ-corse.fr/ ➙ OBJECTIVE: develop a coupled fire-atmosphere simulation prototype Biomass thermal degradation VEGETATION SCALES Combustion processes Surface/atmosphe re interactions FLAME SCALE ATMOSPHERIC SCALES Atmospheric dynamics and emissions FIRE/ATMOSPHERE MODEL ● ● ● Coupling strategy 17 INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX

18. INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX FIRE/ATMOSPHERE MODEL ● ● ● Coupling strategy 18 • Lagrangian representation of the subgrid-scale fire front Atmospheric model grid size (∼ 50 m) VEGETATION • Terrain data • Distribution: using CORINE ESA database and forest inventory (BDForêt) ➙ Sensible heat flux ➙ Water vapor flux ➙ Radiant temperature ➙WIND •Interpolation at the front markers •assumed constant over one model time step •1-D boundary layer model (mid- grid)

19. INTRODUCTORY SEMINAR May 2014Mélanie ROCHOUX FIRE/ATMOSPHERE MODEL ● ● ● Coupling strategy 19 • Introduction of a burning matrix • Burning ratio Rb = ratio of the burning area over the atmospheric grid area, ranging from 0 (no fire) to 1 (all burning). • 1 value of burning ratio per atmospheric model grid box SURFACE FLUXES REQUIRE: • Nominal convection heat flux • Nominal water loading • Nominal flame temperature Tn (1000 K) • Soil temperature from the atmospheric model Ts ➙ Sensible heat flux ➙ Water vapor flux ➙ Radiant temperature FORMULATION OF THE EQUIVALENT RADIANT TEMPERATURE Te: Te 4 = (1 - Rb) Ts 4 + Rb Tn 4

20. INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX FIRE/ATMOSPHERE MODEL ● ● ● Coupling strategy 20 • Limitations in surface wildfire spread modeling • Physical modeling inaccuracies ➙ Heat transfer to vegetation ➙ Local and steady-state assumption (canyons) • Absence of modeling for fire/atmosphere interactions Favone wildfire (30 ha) FOREFIRE Coupled Observed Two-way fire/atmosphere coupling FOREFIRE/MESO-NH

21. INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX FIRE/ATMOSPHERE MODEL ● ● ● Atmospheric chemistry 21 • Emission sources • Emissions during the biomass thermal degradation (e.g. soot particles) • Incomplete combustion ➙ Sensible heat flux ➙ Water vapor flux ➙ Radiant temperature ➙ Gas species emission • Species emitted in the surface layer (injection model) and mixed by the turbulence scheme (mainly CO) • Distinction of flaming and smoldering modes of combustion in the injection model • Emission factor database still incomplete, in particular for Mediterranean ecosystems

22. INTRODUCTORY SEMINAR June 13, 2014Mélanie ROCHOUX FIRE/ATMOSPHERE MODEL ● ● ● Atmospheric chemistry 22 • Transport and chemistry in the smoke plume • No parameterization of the smoke injection height ➙ explicit calculation • ReLACS chemical kinetic scheme used in MÉSO-NH (no aerosol scheme) Fire/Surface ➙ Vegetation ➙ Topography Fire/Atmosphere ➙ Dynamics ➙ Chemistry Turbulence Gases & Aerosols Wind Case study : Lançon de Provence (2005), Strada et al. 2012

23. SOURCES ➙ High-resolution biomass fuel ➙ Combustion ➙ Emission models ATMOSPHERE ➙ Dynamics of the smoke plume ➙ Chemistry (aerosols) ➙ Feedbacks on fire Overview of fire research OBSERVATIONS ➙ Detection ➙ Monitoring