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<p>Flame shape and heat flux are crucial indicators for evaluating forest combustion conditions. Variations in surface fire spread rate caused by changes in fuel and terrain conditions correspond to distinct flame shape and heat flux characteristics. However, little is known about the relationships among flame shape, heat flux, and surface fire spread rate after alterations in fuel conditions (such as moisture content and load) and slope. We selected <i>Pinus koraiensis</i>, <i>P. sylvestris</i> var. <i>mongolica</i>, <i>Quercus mongolica</i>, and <i>Juglans mandshurica</i> in Heilongjiang Province, China, whose surface fuel bed structures and fuel types differ. We analyzed the impacts of changes in fuel moisture content, load, and slope on the surface fire spread rate, flame shape, and heat flux characteristics. Additionally, we evaluated the relationships among flame shape, heat flux, and surface fire spread rate under varying moisture content, load, and slope conditions. Moisture content is negatively correlated with the surface fire spread rate, flame shape, and heat flux characteristics, while fuel load exhibits the opposite trend. Slope is positively correlated only with flame size (height and length) and indicators of total and convective heat fluxes. Increases in moisture content and slope exert direct negative and positive impacts on surface fire spread rate respectively. In contrast, an increase in fuel load produces only an indirect positive impact on the spread rate through the peak total heat flux and flame height, with no significant direct effect. Both increases in moisture content and slope indirectly negatively affect the spread rate through flame height. However, the negative impact of slope is offset by its positive effect through the peak total heat flux, resulting in an overall positive indirect effect. The surface fire spread rate directly responds to changes in moisture content and slope and indirectly enhances its responsiveness through flame shape and heat flux. In contrast, the response of the spread rate to changes in fuel load is mediated by flame shape and heat flux. This study enhances the understanding of the theoretical mechanisms by which changes in fuel and terrain conditions influence the surface fire spread rate.</p>

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Flame shape and heat flux mediate conditions of fuel and terrain affect surface fire spread rate

  • 期刊论文

  • 发表日期：

    2026年6月16日

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  • Yan Guo,
  • Haiqing Hu,
  • Ziyuan Man,
  • Tongxin Hu,
  • Long Sun

摘要

Flame shape and heat flux are crucial indicators for evaluating forest combustion conditions. Variations in surface fire spread rate caused by changes in fuel and terrain conditions correspond to distinct flame shape and heat flux characteristics. However, little is known about the relationships among flame shape, heat flux, and surface fire spread rate after alterations in fuel conditions (such as moisture content and load) and slope. We selected Pinus koraiensis, P. sylvestris var. mongolica, Quercus mongolica, and Juglans mandshurica in Heilongjiang Province, China, whose surface fuel bed structures and fuel types differ. We analyzed the impacts of changes in fuel moisture content, load, and slope on the surface fire spread rate, flame shape, and heat flux characteristics. Additionally, we evaluated the relationships among flame shape, heat flux, and surface fire spread rate under varying moisture content, load, and slope conditions. Moisture content is negatively correlated with the surface fire spread rate, flame shape, and heat flux characteristics, while fuel load exhibits the opposite trend. Slope is positively correlated only with flame size (height and length) and indicators of total and convective heat fluxes. Increases in moisture content and slope exert direct negative and positive impacts on surface fire spread rate respectively. In contrast, an increase in fuel load produces only an indirect positive impact on the spread rate through the peak total heat flux and flame height, with no significant direct effect. Both increases in moisture content and slope indirectly negatively affect the spread rate through flame height. However, the negative impact of slope is offset by its positive effect through the peak total heat flux, resulting in an overall positive indirect effect. The surface fire spread rate directly responds to changes in moisture content and slope and indirectly enhances its responsiveness through flame shape and heat flux. In contrast, the response of the spread rate to changes in fuel load is mediated by flame shape and heat flux. This study enhances the understanding of the theoretical mechanisms by which changes in fuel and terrain conditions influence the surface fire spread rate.