scholarly journals Sensitivity Experiments of the Local Wildland Fire with WRF-Fire Module

2019 ◽  
Vol 56 (4) ◽  
pp. 533-547
Author(s):  
Shaojun Lai ◽  
Haishan Chen ◽  
Fen He ◽  
Weijie Wu
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wildland Fire ◽  
Fire Spread ◽  
Fire Intensity ◽  
Pine Barrens ◽  
Near Surface ◽  
Fire Model ◽  
Sensitivity Experiments ◽  
Fire Area

AbstractIn this paper, it is discussed the performance of the Weather Research and Forecasting (WRF) model coupled with a wildland fire-behavior module (WRF-Fire model) by the observational data collected in an experiment with a low-intensity prescribed fire (LIPF) conducted in the New Jersey Pine Barrens (NJPB) on March 6, 2012. The sensitivity experiments of the WRF-Fire model are carried out to investigate the interactions between the wildland fire and the atmospheric planetary boundary layer. The two-way WRF-Fire model conofigured with fire and large eddy simulation (LES) mode is used to explore the fire characteristics of perimeter shape, intensity, spread direction and external factors of wind speed, and to discuss how these external parameters affect the fire, and the interactions between the atmosphere and fire. Results show that the sensitive experiments can provide the meteorological elements close to observations, such as the temperatures, winds and turbulent kinetic energy near the surface in the vicinity of the fire. The simulations also can reproduce the fire spread shape and speed, fire intensity, and heat flux released from fire. From the view of energy, the heat flux feed back to the atmospheric model and heat the air near the surface, which will induce strong thermal and dynamic instability causing strong horizontal convergence and updraft, and form the fire-induced convective boundary layer. The updraft will be tilted downstream of the fire area based on the height of the ambient winds. Due to the effect of the this updrafts, the particles and heat from the fuel combustion can be transported to the downwind and lateral regions of the fire area. Meanwhile, there is a downdraft flow with higher momentum nearby the fire line transporting fresh oxygen to the near surface, which will increase winds behind the fire line, accelerate the rate of spread (ROS) and make the fire spread to a larger area. Ultimately, a fire-induced climate is established.

scholarly journals WRF-Fire: Coupled Weather–Wildland Fire Modeling with the Weather Research and Forecasting Model

2013 ◽  
Vol 52 (1) ◽  
pp. 16-38 ◽  
Author(s):  
Janice L. Coen ◽  
Marques Cameron ◽  
John Michalakes ◽  
Edward G. Patton ◽  
Philip J. Riggan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wildland Fire ◽  
Weather Prediction ◽  
Fire Behavior ◽  
Atmospheric Model ◽  
Fire Intensity ◽  
Weather Research And Forecasting ◽  
Spread Rate ◽  
Near Surface ◽  
Weather Research

AbstractA wildland fire-behavior module, named WRF-Fire, was integrated into the Weather Research and Forecasting (WRF) public domain numerical weather prediction model. The fire module is a surface fire-behavior model that is two-way coupled with the atmospheric model. Near-surface winds from the atmospheric model are interpolated to a finer fire grid and are used, with fuel properties and local terrain gradients, to determine the fire’s spread rate and direction. Fuel consumption releases sensible and latent heat fluxes into the atmospheric model’s lowest layers, driving boundary layer circulations. The atmospheric model, configured in turbulence-resolving large-eddy-simulation mode, was used to explore the sensitivity of simulated fire characteristics such as perimeter shape, fire intensity, and spread rate to external factors known to influence fires, such as fuel characteristics and wind speed, and to explain how these external parameters affect the overall fire properties. Through the use of theoretical environmental vertical profiles, a suite of experiments using conditions typical of the daytime convective boundary layer was conducted in which these external parameters were varied around a control experiment. Results showed that simulated fires evolved into the expected bowed shape because of fire–atmosphere feedbacks that control airflow in and near fires. The coupled model reproduced expected differences in fire shapes and heading-region fire intensity among grass, shrub, and forest-litter fuel types; reproduced the expected narrow, rapid spread in higher wind speeds; and reproduced the moderate inhibition of fire spread in higher fuel moistures. The effects of fuel load were more complex: higher fuel loads increased the heat flux and fire-plume strength and thus the inferred fire effects but had limited impact on spread rate.

scholarly journals The Role of Latent Heat Flux in Tropical Cyclogenesis over the Western North Pacific: Comparison of Developing versus Non-Developing Disturbances

2019 ◽  
Vol 7 (2) ◽  
pp. 28 ◽  
Author(s):  
Si Gao ◽  
Shengbin Jia ◽  
Yanyu Wan ◽  
Tim Li ◽  
Shunan Zhai ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
North Pacific ◽  
Western North Pacific ◽  
Specific Humidity ◽  
Near Surface ◽  
Tangential Wind

The possible role of air–sea latent heat flux (LHF) in tropical cyclone (TC) genesis over the western North Pacific (WNP) is investigated using state-of-the-art satellite and analysis datasets. The authors conducted composite analyses of several meteorological variables after identifying developing and non-developing tropical disturbances from June to October of the period 2000 to 2009. Compared to the non-developing disturbances, increased LHF underlying the developing disturbances enhances boundary–layer specific humidity. The secondary circulation then transports more boundary–layer moisture inward and upward and, thus, induces a stronger moist core in the middle troposphere. Accordingly, the air in the core region ascends following a warmer moist adiabat than that in the environment and results in a stronger upper-level warm core, which is associated with a stronger near-surface tangential wind based on the thermal wind balance. This enlarges the magnitude and negative radial gradient of LHF and, thereby, further increases boundary–layer specific humidity. A tropical depression forms when the near-surface tangential wind increases to a certain extent as a result of the continuing positive feedback between near-surface wind and LHF. The results suggest an important role of wind-driven LHF in TC genesis over the WNP.

Role of horizontal eddy diffusivity within the canopy on fire spread

2020 ◽  
Author(s):  
Yana Bebieva ◽  
Kevin Speer
Keyword(s):  
Boundary Layer ◽  
Lower Boundary ◽  
Theoretical Models ◽  
Eddy Diffusivity ◽  
Fire Spread ◽  
Fire Intensity ◽  
Canopy Layer ◽  
Fuel Layer ◽  
1D Model ◽  
Eddy Dynamics

<p>Wind profile observations are used to estimate turbulent properties in the atmospheric boundary layer from 1 m up to 300 m height above north Florida pine woods. Basic turbulence characteristics of the lower boundary layer are presented. Together with theoretical models for the mean horizontal velocity we derive the lateral diffusivity using Taylor's frozen turbulence hypothesis in the surface fuel layer (tens of centimeters). This parameter is used to predict the spread of surface fires in a simple 1D model. Initial assessments of sensitivity of the fire spread rates to the lateral diffusivity are made. Estimated lateral diffusivity with and without fire are made and associated fire spread rates are explored. Our results support the conceptual framework that eddy dynamics in the fuel layer is set by larger eddies developed in the canopy layer aloft. The presence of fire modifies the eddy structure depending on the fire intensity.</p>

scholarly journals Applications of simulation-based burn probability modelling: a review

2019 ◽  
Vol 28 (12) ◽  
pp. 913 ◽  
Author(s):  
Marc-André Parisien ◽  
Denyse A. Dawe ◽  
Carol Miller ◽  
Christopher A. Stockdale ◽  
O. Bradley Armitage
Keyword(s):  
Wildland Fire ◽  
Fire Hazard ◽  
Fire Spread ◽  
Simulation Modelling ◽  
Fire Intensity ◽  
Fire Behaviour ◽  
Direct Examination ◽  
Burn Probability ◽  
Spatial Estimates ◽  
Hazard And Risk

Wildland fire scientists and land managers working in fire-prone areas require spatial estimates of wildfire potential. To fulfill this need, a simulation-modelling approach was developed whereby multiple individual wildfires are modelled in an iterative fashion across a landscape to obtain location-based measures of fire likelihood and fire behaviour (e.g. fire intensity, biomass consumption). This method, termed burn probability (BP) modelling, takes advantage of fire spread algorithms created for operational uses and the proliferation of available data representing wildfire patterns, fuels and weather. This review describes this approach and provides an overview of its applications in wildland fire research, risk analysis and land management. We broadly classify the application of BP models as (1) direct examination, (2) neighbourhood processes, (3) fire hazard and risk and (4) integration with secondary models. Direct examination analyses are those that require no further processing of model outputs; they range from a simple visual examination of outputs to an assessment of alternate states (i.e. scenarios). Neighbourhood process analyses examine patterns of fire ignitions and subsequent spread across land designations. Fire hazard combines fire probability and a quantitative assessment of fire behaviour, whereas risk is the product of fire likelihood and potential impacts of wildfire. The integration with secondary models represents situations where BP model outputs are integrated into, or used in conjunction with, other models or modelling platforms.

scholarly journals Resolving vorticity-driven lateral fire spread using the WRF-Fire coupled atmosphere-fire numerical model

2014 ◽  
Vol 2 (5) ◽  
pp. 3499-3531 ◽  
Author(s):  
C. C. Simpson ◽  
J. J. Sharples ◽  
J. P. Evans
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Wildland Fire ◽  
Fire Spread ◽  
Lateral Spread ◽  
Grid Spacing ◽  
Spread Rate ◽  
Model Framework ◽  
Fire Model ◽  
Horizontal Grid

Abstract. Fire channelling is a form of dynamic fire behaviour, during which a wildland fire spreads rapidly across a steep lee-facing slope in a direction transverse to the background winds, and is often accompanied by a downwind extension of the active flaming region and extreme pyro-convection. Recent work using the WRF-Fire coupled atmosphere-fire model has demonstrated that fire channelling can be characterised as vorticity-driven lateral fire spread (VDLS). In this study, 16 simulations are conducted using WRF-Fire to examine the sensitivity of resolving VDLS to spatial resolution and atmosphere-fire coupling within the WRF-Fire model framework. The horizontal grid spacing is varied between 25 and 90 m, and the two-way atmosphere-fire coupling is either enabled or disabled. At high spatial resolution, the atmosphere-fire coupling increases the peak uphill and lateral spread rate by a factor of up to 2.7 and 9.5. The enhancement of the uphill and lateral spread rate diminishes at coarser spatial resolution, and VDLS is not modelled for a horizontal grid spacing of 90 m. The laterally spreading fire fronts become the dominant contributors of the extreme pyro-convection. The resolved fire-induced vortices responsible for driving the lateral spread in the coupled simulations have non-zero vorticity along each unit vector direction, and develop due to an interaction between the background winds and vertical return circulations generated at the flank of the fire front as part of the pyro-convective updraft. The results presented in this study demonstrate that both high spatial resolution and two-way atmosphere-fire coupling are required to reproduce VDLS within the current WRF-Fire model framework.

scholarly journals The Role of Heat Flux in an Idealised Firebreak Built in Surface and Crown Fires

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1395
Author(s):  
Nazmul Khan ◽  
Khalid Moinuddin
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Wildland Fire ◽  
Heat Fluxes ◽  
Fire Intensity ◽  
Propagation Mode ◽  
Crown Fire ◽  
Eddy Simulation ◽  
Dynamic Simulator ◽  
Fire Dynamic Simulator

The disruptions to wildland fires, such as firebreaks, roads and rivers, can limit the spread of wildfire propagating through surface or crown fire. A large forest can be separated into different zones by carefully constructing firebreaks through modification of vegetation in firebreak regions. However, the wildland fire behaviour can be unpredictable due to the presence of either wind- or buoyancy-driven flow in the fire. In this study, we aim to test the efficacy of an idealised firebreak constructed by unburned vegetation. The physics-based large eddy simulation (LES) simulation is conducted using Wildland–urban interface Fire Dynamic Simulator (WFDS). We have carefully chosen different wind velocities with low to high values, 2.5~12.5 m/s, so the different fire behaviours can be studied. The behaviour of surface fire is studied by Australian grassland vegetation, while the crown fire is represented by placing cone-shaped trees with grass underneath. With varying velocity and vegetation, four values of firebreak widths (Lc), ranging from 5~20 m, is tested for successful break distance needed for the firebreak. For each failure or successful firebreak width, we have assessed the characteristics of fire intensity, mechanism of heat transfer, heat flux, and surface temperature. It was found that with the inclusion of forest trees, the heat release rate (HRR) increased substantially due to greater amount of fuel involved. The non-dimensional Byram’s convective number (NC) was calculated, which justifies simulated heat flux and fire characteristics. For each case, HRR, total heat fluxes, total preheat flux, total preheat radiation and convective heat flux, surface temperature and fire propagation mode are presented in the details. Some threshold heat flux was observed on the far side of the firebreak and further studies are needed to identify them conclusively.

scholarly journals A GIS-based fire spread simulator integrating a simplified physical wildland fire model and a wind field model

2017 ◽  
Vol 31 (11) ◽  
pp. 2142-2163 ◽  
Author(s):  
D. Prieto Herráez ◽  
M. I. Asensio Sevilla ◽  
L. Ferragut Canals ◽  
J. M. Cascón Barbero ◽  
A. Morillo Rodríguez
Keyword(s):  
Wind Field ◽  
Field Model ◽  
Wildland Fire ◽  
Fire Spread ◽  
Fire Model ◽  
Wind Field Model

scholarly journals Boundary-layer turbulent processes and mesoscale variability represented by numerical weather prediction models during the BLLAST campaign

2016 ◽  
Vol 16 (14) ◽  
pp. 8983-9002 ◽  
Author(s):  
Fleur Couvreux ◽  
Eric Bazile ◽  
Guylaine Canut ◽  
Yann Seity ◽  
Marie Lothon ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Weather Prediction ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Mesoscale Variability ◽  
Near Surface ◽  
Order Of Magnitude

Abstract. This study evaluates the ability of three operational models, with resolution varying from 2.5 to 16 km, to predict the boundary-layer turbulent processes and mesoscale variability observed during the Boundary Layer Late-Afternoon and Sunset Turbulence (BLLAST) field campaign. We analyse the representation of the vertical profiles of temperature and humidity and the time evolution of near-surface atmospheric variables and the radiative and turbulent fluxes over a total of 12 intensive observing periods (IOPs), each lasting 24 h. Special attention is paid to the evolution of the turbulent kinetic energy (TKE), which was sampled by a combination of independent instruments. For the first time, this variable, a central one in the turbulence scheme used in AROME and ARPEGE, is evaluated with observations.In general, the 24 h forecasts succeed in reproducing the variability from one day to another in terms of cloud cover, temperature and boundary-layer depth. However, they exhibit some systematic biases, in particular a cold bias within the daytime boundary layer for all models. An overestimation of the sensible heat flux is noted for two points in ARPEGE and is found to be partly related to an inaccurate simplification of surface characteristics. AROME shows a moist bias within the daytime boundary layer, which is consistent with overestimated latent heat fluxes. ECMWF presents a dry bias at 2 m above the surface and also overestimates the sensible heat flux. The high-resolution model AROME resolves the vertical structures better, in particular the strong daytime inversion and the thin evening stable boundary layer. This model is also able to capture some specific observed features, such as the orographically driven subsidence and a well-defined maximum that arises during the evening of the water vapour mixing ratio in the upper part of the residual layer due to fine-scale advection. The model reproduces the order of magnitude of spatial variability observed at mesoscale (a few tens of kilometres). AROME provides a good simulation of the diurnal variability of the turbulent kinetic energy, while ARPEGE shows the right order of magnitude.

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