DETERMINING CONVECTIVE/RADIATIVE ENERGY PARTITIONING IN LARGE SCALE OPEN VEGETATION FIRES

"The wildland fire grand measurement challenge can be described as the integration of pre- active- and post-fire measurements and physical process models into a robust and well validated framework for characterizing coupled fire-atmosphere dynamics, fire emissions, [...] at a range of scales from flame fronts to prescribed and wildfire events" (Kremens et al. 2010). This small grant project is inspired by this "grand" challenge of the fire research community. In particular, fire behavior and fire emissions are largely driven by energy releases. Understanding the energy budget of a propagating fire requires us to know simultaneously both the Radiative Heat Fluxes (RHF) and Convective Heat Fluxes (CHF), and to relate them to the total heat release (THR) of the combusted fuel. This is a challenging task because (i) the degree to which scaling of fire properties from small scale lab experiments to open vegetation fires can be performed is uncertain, and (ii) CHF and RHF cannot be linked by single point measurement since the plume (the 'visible' manifestation on the CHF) is usually advected from its source action (i.e. the fire front) by the ambient wind. To tackle these issues, we need to develop a protocol able to map simultaneously CHF and RHF under the conditions present in large outdoor "planned" fires.

Such comprehensive sets of data linking energy partitioning from fuel consumption with the various modes of heat loss are unavailable currently, and indeed such measurements have not been conducted before. According to the work realised by the proposers of this project and co-workers on FRP measurement protocols and radiative heat flux assessment via airborne thermal imagery, spatio-temporal variations of the RHF from spreading vegetation fires can however be mapped. To close the energy budget, we then need (i) to measure the fuel mass burnt to derive THR (which can be easily assessed with pre- and post- fire in situ sampling) and (ii) to map CHF to allow comparison with the RHF measure.

The aim of this proposal is therefore to develop the experimental measurement protocol and infrastructure capable of recording simultaneously the temporal and spatial variability of radiative (RHF) and convective (CHF) heat fluxes in spreading vegetation fires, and to deploy this at a series of experimental burns in order to deliver a record of fire energy partitioning for such events. This project will link to one ongoing and one newly commencing projects lead by Prof Martin Wooster. In particular, NERC KE project NE/J006432/1 that will run in collaboration with the Northumberland Fire and Rescue Service will provide many opportunities to develop, validate, and deploy the methodology at prescribed fires planned to occur in the UK over the next few years. To our knowledge this is the first time that such an experiment will be conducted, and the results will be made available to the fire science community for their use in the evaluation, improvement and running of a variety of simulation models.

As outlined in the "pathways to impact" document - since the topic of this project is mainly driven by physical concepts, i.e. the energy partition of spreading fire, the main beneficiaries are essentially academics working in the fire research community (as stated in the Academic Beneficiaries section of this proposal). The project proposers are in close contact with research groups working on such topics in the UK (e.g. the Fire Engineering Department of the University of Edinburgh; the Fire Research Centre based in the School of Mathematics of the University of Manchester) and internationally (e.g. the Fire Group of NIST who develop the physically based fire model WFDS. Many of these contacts have been developed through past or current NERC funded projects.

Other communities of emission modellers and atmospheric transport modellers would also been interested in the results of our work since the issue of the injection height of biomass burning plumes is still an on-going research problem, and improved knowledge of the fire energy budget would help to develop further some of the current parameterizations (e.g. Frietas et al., 2007) already in use within several global atmospheric models. In time this would eventually improve our understanding of the role of wildfire in global carbon dynamics (IPCC, 2007). At this level, the European Center for Medium-Range Weather Forecasts (ECMWF) would benefit directly from this small NERC project as it is involved in the commencing (Oct. 2011) KE NERC project lead by the current proposal team which aims to implement in their forecast model a real-time based parameterization of biomass burning injection height.

In the longer term this work could impact several communities such as (i) fire fighters and land managers in their planning and incident management procedures, through improving fire spread models and (ii) air quality agencies by improving the representation of real-time monitoring and medium term forecasting of atmospheric chemistry and air pollution related to the transport of biomass burning smoke. To reach these different communities, this "small grant" project could count on past and present collaborations of the proposal team with (i) the Fire and Rescue Service of Northumberland (NERC project NE/J006432/1) and (ii) the Environmental Research Group of Kings college London responsible of air quality forecasting related to UK health impacts (NERC project NE/I022116/1).

As outlined in the "pathways to impact" document, the direct academic impact of the results generated by this proposal will be published in appropriate journals (e.g. Int. J. Wildland Fire or Atmospheric Measurement Tech.) and presented at UK and European conferences, and the raw CHF, RHF and THR data placed on the website wildfire.geog.kcl.ac.uk and the British Academic Data Center (BADC) for use by the fire measurement and modelling communities.