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预测森林大火与阻止火势蔓延的实验

更新时间:2018-11-3 8:10:15 来源:千亿千亿国际娱乐官网 作者:佚名

The quest to predict-and stop-the spread of wildfires
预测森林大火与阻止火势蔓延的实验

Mark Finney at the US Forest Service and his colleagues sometimes do the unthinkable. They go out into the bush and start a fire. But they’re not arsonists and these fires aren’t sprawling or highly destructive. They’re controlled burns of real vegetation that give scientists a better understanding of how flames leap from one branch to another. Studying that can help predict how real wildfires may spread.

美国林务局的芬尼(Mark Finney)和同事们有时会做些不可思议的事——去灌木丛里放火。但他们可不是什么纵火犯,火势也不会肆意蔓延,或者带来巨大破坏。这些都是对真实植被进行的有控制的燃烧,以便科学家们更好地了解火焰的传递,从而帮助预测真实火情如何蔓延。

Among the measurements Finney and his team take include the amount of time that flames spend burning in one area, how quickly they propagate through vegetation and what kind of heat exchange is going on as they do so. These experiments have taken place in New Zealand. The burn areas are cordoned off by barriers that stop the fire getting out of control.

芬尼及其团队会测定火焰在一个区域内的燃烧时间、在植被中的蔓延速度,以及在这个过程中有哪些热交换。这些实验在新西兰进行,燃烧区域用障碍物隔开,以防火势失控。

“We have drones that fly over and give us a view of what’s going on from the air, we have cameras that are protected by an aluminium and insulation housing that allow you to put them inside the fire,” he says. “It usually takes a day or more to set up all the instruments and of course you have to have the weather conditions cooperating.”

“我们动用了无人机拍摄空中角度,还有用铝质绝缘材料保护的摄像头,可以把它们放在火里面拍摄,”他说。“通常需要一天甚至更多时间来准备好所有设备,当然,还得老天爷配合。”

It’s all part of a modern human quest – to know what makes fire tick.  A supposedly crucial moment in the history of human evolution is the “discovery” of fire. But fire has been a natural occurrence on Earth since long before our ancestors took their first steps. And today, far from being something under our control, fire often takes the form of a man-made disaster. In the US, well over 80% of wildfires are started, usually accidentally, by people.

这是现代人类的一项探索——了解火的原理。火的“发现”是人类进化史上的一个关键时刻。但在此很久之前,火就一直在地球上自然存在着。今天,火还远非我们所能控制,而且经常是人为酿成的灾难。在美国,80%的大火都是人类引发,通常是出于意外。

This year, like last year, many parts of the planet have experienced very hot and dry summers, sharply raising the chance of wildfires taking hold once ignited.

今年跟去年一样,地球上许多地方夏天都异常炎热干燥,一有明火,酿成大火的几率大大增加。

Woodlands have blazed in Greece, Sweden, and Siberia among other hotspots. The southwestern US state of California has just recorded its largest wildfire on record.

在希腊、瑞典和西伯利亚等火灾热点地区的林地都有火情发生。美国西南部的加利福尼亚州刚刚录得有史以来最严重的大火。

What if we’d known when and where these fires would start? Or how they would wax and wane? If we had such knowledge, we’d surely be better able to protect the towns and communities that are at risk from destruction.

如果我们能提前知道火灾发生的时间和地点呢?又或是知道火势是如何增强以及减弱的?如果我们掌握了这些知识,肯定能够更好地保护城镇和社区免遭大火破坏。

Finney hopes that data from his experiments will improve the existing models that are used to project wildfire spread. Some of those models are too simplistic, he explains.

芬尼希望他的实验数据能够改善现有预测火势蔓延的模型。他说现在的一些模型太过简单。

“There’s so many things that we can’t use right now in models – like wind variability. The wind is never constant in speed or direction,” he says. “Yet our models are so crude that they require a single input for wind.”

“很多参数目前无法用在模型中——比如风的变化。风的速度和方向从来不是恒定的,”他说。“然而,我们的模型太简陋了,只有一个风的变量设定。”

Over time, the accuracy of these tools is definitely improving, however. In July, a review of Australian wildfire models used to predict fire spread was published. It found that there had been a significant increase in the accuracy of such systems in recent years, reducing errors in their predictions by more than 50%.

不过,随着时间的推移,这些工具的准确度肯定会越来越高。今年7月,有一篇文章分析了澳大利亚预测大火蔓延的模型,发现近年来这类模型的准确性有了显着提高,预测误差减少了50%以上。

What about predicting fires even before they have started? While pinpoint projections of wildfire occurrence are not possible, science is giving us new and better ways of calculating fire risk – and it is helping us understand how major fires may grow once they’ve begun.

在火灾发生之前就做出预测怎么样?虽然不可能进行精确预测,但科学为我们提供了新方法,能更好地计算火灾风险,帮助我们了解一旦大火开始会如何发展。

Max Joseph is a man who knows that there are secrets in data. He and colleagues at the University of Colorado Boulder’s Earth Lab have pulled together a startling array of insights – from how diseases spread to the effect of climate change on animal populations. But lately, he has turned his attention to fire.

约瑟夫(Max Joseph)知道,数据中藏着秘密。他和科罗拉多大学博尔德分校地球实验室的同事们搜集了一系列令人吃惊的说法——从疾病如何传播到气候变化对动物数量的影响,包罗万象。但最近,他把注意力转向了火。

He recently co-authored a study, currently undergoing peer-review, that explored the possibility of predicting which regions in the continental US might be prone to wildfires based on their ecosystems and characteristic weather patterns.

不久前,他跟人合着了一篇研究论文,探讨了是否可以根据生态系统和天气特征来预测美国大陆哪些地区会发生大火,文章目前正在接受同行的评审。

The team gathered weather data going back to 1984, along with information on wildfires that had occurred since then. A computer model analysed the relationship between weather patterns and outbreaks of fire. They found that generally, periods of low humidity – dry air – and high temperature were particularly good indicators of fire risk. More so than rainfall.

他们搜集了自1984年以来的天气数据以及大火的信息,用计算机模型分析了天气和火灾爆发的关系。他们发现,一般来说,低湿度(即空气干燥)和高温往往预示着火灾风险系数高,比降雨量更有指示作用。

How such conditions affected fires varied greatly from one “ecoregion” to another – areas of differing terrain and vegetation. But by picking up patterns in data spanning 1984-2010, the model proved accurate at predicting fire occurrence in specific regions over the following five years.

“生态区”的地形和植被不同,对火灾的影响也大相径庭。但借助1984至2010年的数据,该模型可以准确预测随后5年某些地区的火灾情况。

“We can predict the number of fires in any one of these regions in a month extremely well,” says Joseph. “99% of the actual numbers were predicted by the model.”

“模型可以非常准确地预测出这些地区中一个月内的火灾数量,”约瑟夫说。“正确率达99%。”

Estimating the size of those fires was more difficult, but the system has given Joseph hope that we can indeed get better at understanding of what areas can expect to see many fires in a certain period, so long as accurate weather data is available in advance.

预测火灾的大小更是难上加难,但这个模型给了约瑟夫希望。只要事先有了准确的天气数据,我们确实可以更好地知道在某段时期哪些区域可能发生大量火灾。

“I think if we can get some good weather predictions, we may be able to have a pretty darn good idea what will happen next year based on this work,” says Joseph.

约瑟夫说:“如果天气预报准确的话,我们也许就能基于这个模型很好地掌握下一年的火灾情况。”

Dominique Bachelet, a climate scientist at Oregon State University, praises the team’s efforts, though she suggests there may be more subtle ways of analysing another factor assessed by the study: housing density. You might think that the risk of fire is directly proportional to how many humans and houses live in an area – but it also depends on what vegetation is available to burn. Perhaps just a small settlement, in a very fire-prone place with lots of flammable vegetation, could become associated with more frequent combustion.

美国俄勒冈州立大学的气候学家巴切莱特(Dominique Bachelet)肯定了该研究小组的努力,不过她也指出,可能有更为巧妙的方法来分析这项研究所评估的另一个因素:房屋密度。你可能认为火灾风险与一个地区的人口和房屋数量成正比,但这也取决于可以燃烧的植被。居民稀少的地区如果位于有很多易燃植物的火灾易发区,可能火灾更加频发。

The range of factors and methods of interpretation when it comes to the statistical analysis of fire are very broad. Take for example a separate study, published in February, which found a relationship between the number of days with more than 2.54mm of rainfall and wildfires in the western US.

火灾统计分析的因素和方法多种多样。例如今年2月发表的另一项研究发现,美国西部降雨量超过2.54毫米的天数与大火之间存在联系。

This is a slightly different metric to the ones used by Joseph’s group, but it is in tune with their findings – less rainfall does mean less water is available to vaporise and contribute to humidity. Again, the consequential dryness of the air was found to be a driver of fires.

这跟约瑟夫团队使用的衡量标准略有不同,但双方的研究结果一致:降雨量少意味着可蒸发的水少,湿度低。因此空气干燥,是引发火灾的一个因素。

As the authors noted: “If decreasing trends in summer precipitation continue, the result will likely be a continuing pattern of dry, warm summers that result in increasingly more severe fire seasons.”

正如文章作者所言:“如果夏季降水继续减少,那么夏天很可能会持续干燥炎热,就会导致越来越严重的火灾季。”

Park Williams at Columbia University’s Lamont-Doherty Earth Observatory says the hot summer was a giveaway that this year would bring significant fires to California.

美国哥伦比亚大学拉蒙特-多尔蒂地球观测站的威廉姆斯(Park Williams)说,炎热的夏季预示着今年加州会出现严重火灾。

“It was record-breaking hot this summer across a lot of California,” he explains. “When you get those temperatures you’re likely to have some really big fires.”

“今年夏天,加州很多地方都出现了破纪录的高温天气,”他解释说。“高温到了这个程度,就很可能发生一些特大火灾。”

Locating hot spots

定位火灾热点

For the people directly affected by wildfires, what really matters is knowing ahead of time whether the area in which they live will be threatened. The unpredictability of the weather is one complicating factor. But fuel – the vegetation available to burn – is also difficult to quantify. How dense, exactly, is that patch of forest? How dry are the fallen branches this summer? There are efforts to better track this, of course, but many are a work in progress.

对于直接受到大火影响的人来说,真正关心的是提前知晓自己居住的地区是否会受到威胁。天气难料是一个复杂的因素,但燃料,也就是可供燃烧的植被,也很难量化。那片森林的密度究竟几何?今年夏天落下的树枝有多干?当然,人们正在想法设法去更好地评定这些因素,但还有许多工作要做。

Most of all, given that humans and lightning account for almost all wildfire ignitions, it’s extremely difficult if not impossible to predict exactly when and where a blaze will start. But that doesn’t mean we can’t get an idea.

最重要的是,人类和闪电几乎是所有大火的起因,要准确预测何时何地有火灾发生,即使不是不可能,也是极其困难的。但这并不意味着我们完全无能为力。

The most accurate weather forecasts we have, a few days in advance, are used by some agencies to create maps of potential fire hotspots in the US.

一些机构会用目前最为准确的天气预报(提前几天的预报)来绘制美国潜在火灾热点图。

“Maps are produced every single day and updated based on forecasted weather conditions that are critical to fire conditions,” says Finney.

芬尼说:“每天都会绘制热点图,并且依据天气情况中对火灾条件至关重要的几个预测进行更新。”

That can help authorities make evacuations in time, or allow for firefighting resources to be brought to the right places.

这可以帮助当局及时疏散民众,或者为需要的地方提供消防资源。

Someone with a particularly strong interest in our knowledge about fire spread is Ellie Graeden at RedZone Analytics. Graeden provides wildfire analysis to commercial clients – including insurance companies. The three main factors her system takes into account, she says, are wind, fuel availability and the topography of the land on which a fire is burning.

红区分析公司(RedZone Analytics)的格雷顿(Ellie Graeden)对火灾蔓延兴趣浓厚,她负责为包括保险公司在内的商业客户提供火情分析。她的系统所考量的三个主要因素分别是风、燃料获取程度和起火地区的地势。

The insurance companies advised by RedZone may sometimes deploy their own firefighting teams if insured property can feasibly be protected from a blaze. Or, they may work with people who have insurance to help them protect their property. The data is also useful for estimating how much a truly devastating fire might cost an insurance firm – which is important for planning how to make compensation available to customers.

红区分析公司的保险公司客户在受保财产有可能从大火中救出时,有时会派出自己的灭火队,或者帮助投保人保护自己的财产。火情蔓延的数据也可以用来估算一场毁灭性的大火会给保险公司带来多大损失——这对于规划理赔非常重要。

“We make these assessments and run our models during events,” says Graeden. “After the fact, we go back and find out how accurate we were.”

“出现火灾时,我们会用自己的模型来评估火情,”格雷顿说。“火灾结束后,我们会检查模型的准确度如何。”

Last year, Graeden says RedZone’s models predicted which homes in Coffey Park, California, would burn in a devastating wildfire there – with more than 90% accuracy. In total, 3,500 properties were destroyed by that fire.

格雷顿说,去年,公司的模型预测了加州科菲公园住宅区有哪些房子会在那场毁灭性的大火中被吞噬,准确率超过90%,大火总计烧毁了3500间房屋。

But even these projections can be improved. Graeden says there is a lack of good, quantitative data on how certain types of homes catch fire and burn. We know that asphalt or clay roofs are less likely to burn than wood ones, for example, but accurate data quantifying the difference between these roofs under fire conditions isn’t readily available, says Graeden.

但这个准确率也还有改进空间。格雷顿说,目前还缺乏可靠的量化数据,来说明各类房屋是如何起火以及燃烧的。例如,我们知道沥青以及土质的屋顶不像木头屋顶那样容易燃烧,但这些屋顶在火灾时的差异究竟如何,还没有精确的量化数据。

What does the future of wildfire look like? The picture is decidedly mixed. On a global scale, the annual total area burned by wildfires is actually decreasing because of the expansion of farmland. In localised places, though, the hot and dry summers we’re experiencing that are linked to climate change are expected to continue causing problematic fires in places we’d rather not have them – such as right next to urban developments.

未来的大火会是什么样?情况显然喜忧参半。全球来看,由于农田的扩张,每年的过火面积实际上在减少。然而,在局部地区,气候变化导致的干热夏季,预计将继续在紧邻城市的开发区等地引起火灾­——虽然我们本来也不想有这些开发区。

Bachelet thinks that what we’re observing now is an unusual, transitional period. Dense, woody forests that for centuries experienced much milder summers than we see today are now reacting to that change in climate – by burning.

巴切莱特认为,现在正是一个非同寻常的过渡期。当前的夏天是几个世纪以来最为炎热干燥的,繁茂的森林面对气候变化也做出了反应——燃烧。

“What regrows after fire will be more adapted to these conditions so will probably produce less fuel,” says Bachelet. The ecosystems in such areas are “resetting”, she explains.

“火灾后重新长出的植被将更加适应现有条件,因此火灾时的可燃材料可能会减少,”巴切莱特说。她表示这些地区的生态系统正在“重置”。

In places like California, years of fighting fires and leaving trees intact on hillsides allowed forests to become even denser than they might have been. That has exaggerated the effect climate change is now having on those forests, adds Williams.

威廉姆斯补充说,在加州这样的地方,与火灾的常年搏斗以及对山林的人为保护,使得森林变得异常茂密,这也放大了气候变化对这些林区的影响。

“The ability of a warming atmosphere to really amplify fires, the table for that was set by there being artificially dense forests,” he says.

他说:“人为茂密起来的森林也确实令气候变暖对火灾的影响有所增强。”

Fire is a natural part of these ecosystems, but the incidence and character of recent fires has undoubtedly been shaped by human activity. “People,” says Bachelet, “should expect fire.”

火是生态系统的自然组成部分,但近些年起火的频率和性质无疑受到了人类活动的影响。巴切莱特说:“人们不该对发生火灾感到奇怪。”

In a warmer world, the inferno seems increasingly capable of threatening our way of life, of bearing down as it so often does, on our towns and our cities. We can’t stop fire in its tracks. Neither will we ever be able to perfectly predict each blaze before it happens. But maybe we can get better at managing fire – and better at getting out of its way.

随着气候逐渐变暖,大火对我们生活方式的威胁越来越大,也一如既往地威胁着大城小镇。我们无法阻止火势蔓延,也永远无法准确预测到每一个火灾,但也许我们可以更好地控制大火,更好地逃离火场。

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