Mika Peace. August 2013

Transcription

1 Fire Advanced Forecasters Course 2013 Bushfire CRC Bureau of School of Mathematical Sciences, Adelaide University August 2013

2 Acknowledgements Fire Thanks to: Graham Mills Lachie McCaw Trent Mattner Jeff Kepert And BMTC (Monica and Duncan)

3 Recap from before lunch... Fire McArthur - focus on surface conditions Kangaroo Island ( Bay and ) and Layman fires FireCAPE Sea breeze convergence Topography Dry air entrainment Plumes and plume development Fire-atmosphere feedback Heat and moisture release Fire-modified winds Convection columns

4 Outline Fire 1 Fire 2 3

5 Fire Where did they originate? What is the difference between a fire model and a fire danger system? What do fire predict? Your thoughts...

6 Fire Originated in forestry / land management as 1D and 2D Mostly from fitting a ROS curve to empirical laboratory or field data Evolved into PC based simulators Fire systems predict elements of a fire Fire danger systems produce indices. What do they predict? ROS, flame length, fire perimeter, fire area, scorch height etc emphasis on ROS for a given wind speed

7 Fire What are the inputs to a fire Your thoughts...

8 Fire What are the inputs? Fuel type, live/dead fuel, fuel moisture, wind speed, and direction. Fuel layers (surface, canopy, understorey) Winds. Question of height of wind speed - 10m, mid-flame height etc.. Wind Wizard, Wind Ninja Slope steepness / topography Quick to run in real time for a fire Nice graphical displays BehavePlus (USA), FARSITE (USA), Phoenix (Australia)

9 BehavePlus (USA) Fire Part of the fire system that includes FARSITE, FlamMap (fire mapping) and FSPro (probability) US Forest Service, National Park Service (+ other USA land management) PC based (quick) 1 dimensional (point data) Tables, graphs and simple diagrams Used for basic fire modelling, prescribed fire planning, predicting wildfire Figure: behaveplus-introduction/behaveplusscreenshots

10 FARSITE (USA) Fire 2-dimensional fire behavior and fire growth simulator (PC based) Spatial and temporal information - topography, fuels, weather (needs GIS) Models for surface fire, crown fire, spotting, post-frontal combustion, and fire acceleration Rothermel s (1972) surface fire spread model (and a crown fire model) Used for ongoing fires and hypothetical fires Figure: bark-beetles-fuels-fire/fsatutorial/ include/overview.html

11 PHOENIX RapidFire fire-spread model (Aust) Fire Landscape fire spread scenario Fire intensity, ember density, flame height, fire size Spotting processes * McArthur MkV and CSIRO grass Used operationally in VIC, testing in other states Challenges with wind inputs Huygens spread algorithm (ellipse shape) Figure: lessons-black-saturday -extreme.html

12 summary Fire Simple weather inputs - wind speed and direction T, Td often not explicit - included as fuel moisture Fuel information - fuel categories, fuel moisture, live/dead fuel, fuel layers Question of wind speed level - 10m, mid-flame height (?) Focus on ROS and fire perimeter Underlying empirical data! Quick to run in real time for a fire Really nice graphical displays (belie the underlying science) All have a steady state assumption for wind and fire spread!

13 What is a fire Fire Includes the heat and moisture released by the fire WRF... Weather Research and Forecasting WRF solves the 5 basic equations governing motion in the atmosphere with parameterisations for sub-grid processes User defined options... domain, physics and dynamics (e.g. turbulence, surface physics, cumulus etc.)

14 WRF-fire Fire Rothermel equations Fire propagation is determined from Rothermel s equations (ie. not McArthur). Rothermel emphasised fuel arrangement rather than weather as inputs Fuel Fuel properties set through Anderson s fuel categories Sensible and latent heat (moisture) flux Calculated from (burnt) fuel quantities for each time interval Sensible heat flux as tendency of θ Latent heat flux as tendency of water vapor

15 WRF-fire Fire Aspects of WRF-fire to consider Fire spread (wind reduction factor) Fuel description (Australian fuels) Fuel moisture constant (dynamic in future) Topographic data inputs Numerical stability (CFL criterion) Spotting processes Crown fires Smoke

16 How have we used? Fire,, working on Layman Initialise with NWP (GFS, ERA-interim) Challenges... (not yet operational) Time to install, compile, run errors etc. Visualisation

17 Fire

18 Wind change acceleration into the fire Fire

19 Wind change acceleration into the fire Fire Feedback on Feedback off

20 Vortex for the ERA-interim. Firewhirls Fire

21 Fire

22 Fire modified winds Fire

23 Fire

24 Fire modified winds Fire

25 One minute data Fire

26 Fire

27 Fire

28 Momentum entrainment Fire

29 Dry air entrainment? Fire

30 1 Fire show we have lots to learn Highlights what we don t know.... No perfect recipe for future forecasting and tricky... seemingly subjective processes Fire atmosphere feedback appears to be more important than hitherto appreciated Fire modified winds can significantly change the fire perimeter The steady state assumption doesn t hold

31 2 Fire Future of fire in Australia - limited funding at present - but agencies want more of them... If we are using un and - we need to appreciate the inputs, limitations and weaknesses. Requirement to re-think of the underlying empirical basis of *all* fire spread and steady-state assumptions.

32 Discussion time Fire model(s) Discussion? Questions?