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Effects of post-fire vegetation regrowth on wind fields over complex terrain
| Content Provider | Semantic Scholar |
|---|---|
| Author | Quill, R. Sharples, J. Sidhu, Leesa A. |
| Copyright Year | 2015 |
| Abstract | The spread of bushfire is highly sensitive to wind speed and direction. Consequently, strong variation of wind fields over areas of complex terrain, with multi-scale changes in topography and surface roughness, significantly complicates the prediction of bushfire behaviour. In the current suite of operational fire modelling schemes, mesoscale variations in wind fields are often over-simplified, thereby reducing the accuracy of fire behaviour modelling in areas of potentially volatile or dangerous fire behaviour. To address this issue, emerging fire modelling frameworks are using ensemble-based approaches to accommodate for the inherent uncertainties in the factors influencing fire behaviour. To account for the effects of wind variability within ensemble approaches it is necessary to recast wind field information in probabilistic terms. As part of an investigation into a probabilistic representation of wind field information, the mountainous region west of Canberra is used as a case study. In particular, analysis is focussed on Flea Creek Valley within the Brindabella Ranges. The valley runs in a north-south direction, approximately perpendicular to the dominant west-north-westerly (WNW) prevailing wind direction. Flea Creek Valley, and much of the surrounding region, was heavily burnt during the 2003 Canberra bushfires but the region has since experienced no major fire activity. In 2007 and 2014, wind data were collected across a 3-4km east-west transect of Flea Creek Valley. To statistically characterise wind fields across complex terrain, the directional response of surface winds to changes in prevailing winds is considered as a toroidal, or bivariate circular, probability distribution. To construct these distributions, wind direction measured on the ridge top (indicative of the prevailing winds) is plotted against the concurrent wind direction measured within the landscape. Discrete observed directional response distributions are taken as noisy realisations of continuous underlying distributions of wind direction response. These continuous distributions can be estimated using a number of mathematical techniques including cubic or thin plate smoothing splines. Both the observed discrete and estimated continuous distributions highlight the modal nature of wind direction response across the landscape. Understanding the impacts of variables such as surface roughness on this directional response is an important step towards spatially extending a statistical characterisation of wind fields across complex terrain. To discern any changes in the probabilistic response caused by changes in surface roughness due to vegetation regrowth, a number of mathematical and statistical comparison techniques are available. In this paper, techniques from astronomy, biometrics and statistics are employed to investigate the effects of seven years of post-fire vegetation regrowth on the directional response of surface winds across Flea Creek Valley. The findings of this study suggest that the choice of statistical test as well as smoothing technique can have a significant impact on the results. Despite this, there is also evidence that the wind response across Flea Creek Valley may have been significantly altered by regrowth in some areas, but in other areas no significant difference is found. There are important implications here for wind and fire modelling, and it is clear that there is much more work to be done to better understand the impacts of physical variables on the probabilistic characterisation of wind fields. |
| File Format | PDF HTM / HTML |
| DOI | 10.36334/modsim.2015.a4.quill |
| Alternate Webpage(s) | http://mssanz.org.au/modsim2015/A4/quill.pdf |
| Alternate Webpage(s) | https://doi.org/10.36334/modsim.2015.a4.quill |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
