CAREER: CONIFER: Role of Canopy Turbulence in Wildland Fire Behavior

职业：针叶树：树冠湍流在荒地火灾行为中的作用

• 批准号: 2146520
• 负责人: Tirtha Banerjee
• 金额: $ 60万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-02-01 至 2027-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2146520&HistoricalAwards=false
• 关键词: CAREER; CONIFER; Role; Canopy; Turbulence

Wildfires have become increasingly more destructive with changing patterns of climate and land-use change. A small number of very large fires have become extremely high-intensity infernos and have been causing the majority of the damage. However, the understanding of the physical processes governing wildland fire behavior has remained limited. Although some research progress has been made in understanding how fires spread on grasslands, several aspects of fire behavior in forested environments are still not well understood. Under certain circumstances, surface fires occurring on a forest floor can ascend vertically and damage the forest canopy. Moreover, if the conditions are favorable, the fire can spread horizontally tree-to-tree across the canopy, becoming a much higher intensity crown fire. Understanding the physical and dynamic meteorology of wildland fires is consequently of utmost importance and necessary to develop mitigation strategies such as prescribed burns and effective fuel management practices such as forest thinning. To assess the effectiveness of such management efforts, it is, therefore, crucial to understand wildland fire behavior inside the forest canopy environment. This project will characterize the mechanisms of turbulent wind flow in the forest canopy during wildland fire events, which will result in (i) advances in fire behavior modeling, (ii) developing decision support tools for fuel treatments and prescribed fires, and (iii) improved models of air quality impacts from wildland fires. Moreover, the project will train a cohort of early-career scientists and students in the fundamentals of wildfire science.In a vegetated environment, the fire occurs below the forest canopy, which means that canopy-induced turbulent eddies interact with the fire and the fire-atmosphere interaction is modulated by the fundamental nature of canopy turbulence. The forest canopy acts as an extended sink of momentum for the air above, thereby imposing a range of length and velocity scales. Moreover, the presence of shear-induced instabilities at the canopy-atmosphere interface results in intermittent coherent structures that penetrate the sub-canopy airspace and aid in canopy-atmosphere interaction. The physics of turbulent flow in vegetated canopies itself is an active area of research to date. Standard atmospheric boundary layer formulations are inadequate in explaining canopy-atmosphere exchange of mass, momentum, and energy. This is rendered further complicated by the presence of the fire, which generates additional shear and buoyancy-induced motions. Using lab and field experimental datasets, this project will explore the following questions: (i) how do the coherent structures imposed by the canopy influence the convective and radiative regimes that regulate fire spread? (ii) how do the unique nature of turbulent transport and turbulent diffusivity in the canopy impact the redistribution of turbulent energy during wildfires? and (iii) how does the intermittent nature of canopy turbulence impact bursting motions associated with fire spread? This project will alter the current fuel-centric perspective, where the vegetation appears as mere fuel to be consumed by the flames, to a new paradigm, where the canopy itself actively modulates the wind and the fire through interactions spanning multiple scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

随着气候模式和土地使用的变化，野火的破坏性越来越大。少数非常大的火灾已经成为极高强度的地狱，并造成了大部分的损失。然而，对野火行为的物理过程的理解仍然有限。尽管在了解草原火灾如何蔓延方面取得了一些研究进展，但森林环境中火灾行为的几个方面仍然没有得到很好的理解。在某些情况下，发生在森林地面上的地表火灾可以垂直上升，破坏森林树冠。此外，如果条件有利，火可以水平地蔓延到整个树冠的树木，成为一个更高强度的冠火。因此，了解荒地火灾的物理和动态气象学对于制定减轻战略（如规定的燃烧）和有效的燃料管理做法（如森林间伐）至关重要和必要。因此，为了评估这种管理工作的有效性，了解林冠环境内的荒地火灾行为是至关重要的。该项目将描述野火事件期间森林冠层中湍流风流的机制，这将导致（i）火灾行为建模的进步，（ii）开发燃料处理和指定火灾的决策支持工具，以及（iii）改进野火对空气质量影响的模型。此外，该项目还将培训一批早期职业科学家和学生掌握野火科学的基本知识。在植被环境中，火灾发生在森林树冠层以下，这意味着树冠层引起的湍流涡旋与火灾相互作用，而火灾与大气的相互作用受到树冠层湍流基本性质的调节。森林的树冠层充当了上方空气的动量汇，从而形成了一系列的长度和速度尺度。此外，存在的剪切诱导的不稳定性在冠层-大气界面的结果在间歇性相干结构，穿透子冠层的空域，并在冠层-大气相互作用的援助。迄今为止，植被冠层中的湍流物理学本身就是一个活跃的研究领域。标准大气边界层公式不足以解释冠层-大气的质量、动量和能量交换。这是呈现进一步复杂的火灾的存在，产生额外的剪切和浮力引起的运动。使用实验室和现场实验数据集，该项目将探讨以下问题：（i）冠层施加的相干结构如何影响调节火灾蔓延的对流和辐射机制？(ii)在林冠中湍流输送和湍流扩散率的独特性质如何影响野火期间湍流能量的再分配？和（iii）冠层湍流的间歇性如何影响与火蔓延相关的突发运动？该项目将改变目前以燃料为中心的观点，即植被只是被火焰消耗的燃料，而新的模式是树冠本身通过跨越多个尺度的相互作用积极地调节风和火。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Historical spatiotemporal changes in fire danger potential across biomes

生物群落潜在火灾危险的历史时空变化

• DOI: 10.1016/j.scitotenv.2023.161954
• 发表时间: 2023
• 期刊: Science of The Total Environment
• 影响因子: 9.8
• 作者: Baijnath-Rodino, Janine A.;Le, Phong V.V.;Foufoula-Georgiou, Efi;Banerjee, Tirtha
• 通讯作者: Banerjee, Tirtha

Quantifying the effectiveness of shaded fuel breaks from ground-based, aerial, and spaceborne observations

• DOI: 10.1016/j.foreco.2023.121142
• 发表时间: 2023-09
• 期刊: Forest Ecology and Management
• 影响因子: 3.7
• 作者: J. Baijnath-Rodino;Alexandre Martinez;R. York;E. Foufoula‐Georgiou;A. Aghakouchak;T. Banerjee

Historical seasonal changes in prescribed burn windows in California

加利福尼亚州规定燃烧窗口的历史季节变化

• DOI: 10.1016/j.scitotenv.2022.155723
• 发表时间: 2022
• 期刊: Science of The Total Environment
• 影响因子: 9.8
• 作者: Baijnath-Rodino, Janine A.;Li, Shu;Martinez, Alexandre;Kumar, Mukesh;Quinn-Davidson, Lenya N.;York, Robert A.;Banerjee, Tirtha
• 通讯作者: Banerjee, Tirtha

Examining the existing definitions of wildland‐urban interface for California

检查加州荒地与城市界面的现有定义

• DOI: 10.1002/ecs2.4306
• 发表时间: 2022
• 期刊: Ecosphere
• 影响因子: 2.7
• 作者: Kumar, Mukesh;Li, Shu;Nguyen, Phu;Banerjee, Tirtha
• 通讯作者: Banerjee, Tirtha

A scale-wise analysis of intermittent momentum transport in dense canopy flows

• DOI: 10.1017/jfm.2022.414
• 发表时间: 2021-10
• 期刊: Journal of Fluid Mechanics
• 影响因子: 3.7
• 作者: S. Chowdhuri;K. Ghannam;T. Banerjee