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干旱、火灾和季风气候的前世今生
热度 2 周浙昆 2020-4-18 14:32
四月的西南除了新冠病毒外,牵动人们心弦的,还有云南的干旱和四川西昌的森林火灾 。在云南,全省因为干旱已经造成了 147.79 万人和 41.73 万头大牲畜饮水困难, 100 条河流断流, 180 座水库干涸,农作物受灾面积已达 460 万亩(春城晚报微信公众号)。这种冬春季的干旱已经不是第一次发生, 2010 年云南水库干涸的照片就曾经走红网络(图 1 )。在四川, 2019 年 3 月 30 日凉山州木里县雅砻江镇发生森林火灾, 31 位救火队员壮烈牺牲的事件又在重演。 2020 年,几乎是相同的时间,相近的地点,同样的事情又在发生。 3 月 30 日下午,四川凉山西昌突发森林大火,火势蔓延危及西昌市区, 18 名消防队员牺牲。为什么干旱和火灾在西南会反反复复的上演,这一切还要从季风气候的前世今生说起。 图1. 云南2010大旱造成水库的干涸 按照气候特点,全球气候类群可以大致分为:内陆气候,海洋气候,沙漠气候,热带气候和季风气候。各种气候类型都有自己的典型特征,比如地中海型气候降雨主要集中在冬春两季,而热带地区全年降雨较为较为均匀(图 2 )。季风气候是全球一种主要的气候类型,其典型特征是大气环流季节性反转所引起的干湿季交替。季风系统直接影响着地球的大气圈、水圈和生物圈,全球 60% 的人口受季风气候的影响。亚洲季风系统建立后,最大的环境效应就是降雨的季节性增强,形成干湿两季的显著变化,造成全年降雨的不均衡。以云南为例,大部分地区全年 80% 以上的降雨集中在夏、秋两季(通常 5 月下旬到 10 月下旬),而冬、春季(通常 11 月至次年 5 月上旬)降雨通常少于全年降雨总量的 15% 。雨季前和雨季中,森林的外貌都会有很大的不同(图 3 )。季风气候条件下,雨热同期非常有利用于农作物的生长。然而,在季风气候下,冬春季干旱就是一种常态,森林火灾也是一种大概率的事件。了解季风气候的形成与演变过程,有助于我们了解气候气候的特征,增强我们科学应对频频发生的冬春季干旱和森林火灾的能力。 图2. 气候类型图 图3. 显示同一地点雨季前和雨季后的森林外貌以及昆明50年降雨图 季风是 热带辐合带 (Intertropical Convergence Zone ITCZ) 季节性迁移的表现,本质上是太阳直射纬度的季节性变化。太阳直射点分别在 12 月 22 日和 6 月 22 日前在南回归线和北回归线之间移动,这种移动,引起上太阳辐射热量在南北回归线之间的变化,而最终形成海洋温度的变化。热带辐合带是全球分布的,季风也就就是全球现象。全球有北美、南美、北非、南非和澳洲 - 印尼等六大季风区(图 4 )。 在这个六大季风区中,亚洲季风和我们的关系最大。亚洲季风又可以细分为东亚季风和南亚季风,前者由于水汽来源于太平洋又称为太平洋季风,后者水汽来源于印度洋有称印度洋季风,也称为西南季风。东亚季风主要影响的区域是亚洲东部的大部分区域,而南亚季风影响印度次大陆和我国云南西部。这两种季风虽然都表现为降雨的季节性差异,但是在诸多细节上又有一些差别。在风向上,印度洋季风,夏季以西南风为主,冬季主要是不十分明显的东北风;太平洋季风夏季以东南风为主,冬季以西北风为主。印度洋季风启程比较晚但是发展快,一般始于 6 月初开始,在一个月内就达到最大影响范围;而太平洋季风在四月启动,但是发展过程慢, 3 月才达到最大影响。从降雨量看,印度洋季风降雨的季节性更明显,全球降雨的 80% 是在雨季,而太平洋季风雨季降雨量为全年降雨的 60% 左右。 图4. 全球季风分布图 亚洲季风是什么时候形成的呢?如果把季风定义为季风是热带辐合带季节性迁移的表现,那么当亚洲大陆的地理位置和今天接近的时候,亚洲季风气候就已经存在了。如此推算,亚洲季风在早白垩世就已经存在了。然而,青藏高原的隆升改变了亚洲季风的形态,使得亚洲季风演变成为我们今天看到的样子。在青藏高原形成以前,中国中部的气候由副热带高压控制。热带辐合带的季节性迁移带来的降雨到达不了这些区域,使得在整个古近纪我国中部横亘着一条横贯东西的干旱带 。青藏高原的形成,改变了亚洲的地形地貌和大气环流,巨大的山体像一台抽水机,将海洋的湿气团吸到我国的中东部地区,使得中国中部的干旱带消失,亚洲季风从热带辐合带季节性迁移为主导的季风,变成由海洋风为主导的现代季风(图 5 )。而中中新世喜马拉雅逐步达到现在的高度,将印度洋的水湿气团带到了印度次大陆甚至深入到我国的西南部,这就是我们说的印度洋季风。可以说没有青藏高原的形成,就没有今天的江南水乡。 图5. 显示青藏高原对大气环流的改变 自从中新世以来,亚洲季风的格局的就基本形成,在全球气候的背景下,诸如,北极冰盖的形成,大气二氧化碳浓度的改变,第四纪冰期等地质事件的影响下,季风的强弱会发生一些改变,比如我们对古气候的重建表明,从中新世到上新世,在云南,季节性进一步的增强,降雨更加的集中于夏季。但是,在总体上现代季风气候所带来的以冬春季为干旱的气候特征就不会改变。认识这一气候特征,有助于我们科学合理的应对冬春季干旱,和冬春季在我国西南频频发生的森林火灾。 以滇中为例, 2010 年也出现程度和今年不相上下的冬春季干旱,再查气象记录,类似的干旱也时有发生,甚至呈现出周期性的规律。冬春季干旱就是云南气候特征的一种常态。受干旱影响较大的滇中地区,全年的降水并不算少。昆明的全年降雨在 800 到 1200毫米 左右,但是这些降雨大多数是集中在雨季,也就是 7-9 月之间。如果我们能够兴修水利,做到科学合理的蓄水,冬春季的干旱的影响就会大大降低。几年前我还是省人大代表的时候,作为代表去视察了一个水库,我记得那个时候是 9 月份,我看到水库的水位很低,水库的闸门被高高的提起,而那一年当地的降雨也比较少。我问水库的负责人,为什么还不关闸蓄水,该负责人回答说,水利部门有一个规定,为了防止洪涝,水库要在 10 月才能蓄水。 10 月已经是雨季的尾声,这时候能蓄的水是非常有限的了。不知道这个情况现在是否得到改变。 说到森林火灾大家都谈虎变色,其实火在森林的更新中,发挥着十分重要的作用,有些物种的种子必须要经常森林火烧后才能萌发。我们的森林面积总体减少,城市面积在扩大,我们承担不起森林火灾的后果。每到旱季,人们对森林火灾可谓是严防死守,但是森林火灾还是频频发生。当然有些火灾是人为因素引起的,但是很多森林火就是一个自然过程,防不胜防。从化石记录中可以看到,在地质历史上,森林火也是经常发生的。既然森林火灾不可避免,做好防范就尤为重要。这种防范并不是发生火灾以后再去灭火,而是在森林中,做好防火隔离带,即使森林火发生,也不至于成片的烧掉整个森林。世间最为珍贵的是生命,失去了就不会再来。 参考文献: 王宇等, 1990. 云南省农业气候资源及区划 . 北京:气象出版社 汪品先, 2009. 全球季风的地质演变 . 科学通报 54: 535-556. Alex Farnsworth et al., 2019. Past East Asian monsoon evolution controlled by paleogeography, not CO2. Sci. Adv. 2019;5: eaax1697 Robert A Spicer, 2017. Tibet, the Himalaya, Asian monsoons and biodiversity e In what ways are they related? Plant Diversity. 39:233-244 Sun X.J., Wang P.X., 2005. How old is the Asian monsoon system?--Palaeobotanical records from China. Palaeogeography, Palaeoclimatology, Palaeoecology 222: 181-222.
个人分类: 科普|8436 次阅读|4 个评论
技术转让:德国航空航天中心森林火灾早期预警系统FireWatch
热度 1 Helmholtz 2013-1-23 16:02
由德国航天航空中心所开发的FireWatch于2001年开始在德国的勃伦登堡开始应用,之后推向欧洲更多国家,另外也包括澳大利亚。 其技术核心是通过红外技术进行旋转扫描,可以在8分钟时间里完成对700平方公里森林的异常烟气与火炎进行检索、比对以及警告。当下成熟的技术产品由德国IQ-Wireless持有( http://www.fire-watch.de/ ),中国市场则由澳大利亚的FireWatch公司负责。单套的产品可以对700平方公司的森林进行早期的烟气与火炎的观察监控,而更大面积的监察,则可以通过多个观测塔的联合运行予以实现。在采用本产品之后,在德国勃伦登堡实现减少工作人员四分之三的良好效果。 中文视频宣传解释: http://www.fire-watch.de/videos#view An Early Warning System for Forest Fires,successfully in the global use FireWatch is a terrestrial, digital, remote surveillance system which is capable of observing larger wooded regions, and to analyse, evaluate, link and store the collective data. Due to its sensitivity, accuracy and reliability the system enables an early recognition of forest fires. FireWatch is able to evaluate and classify the incoming data in multiple ways, connected to a central station. In the event of a recognized source of fire, it automatically sends out an alarm. FireWatch protects entire eco-systems and cultural landscapes. An Early Warning System for Forest Fires,successfully in the global use FireWatch is a terrestrial, digital, remote surveillance system which is capable of observing larger wooded regions, and to analyse, evaluate, link and store the collective data. Due to its sensitivity, accuracy and reliability the system enables an early recognition of forest fires. FireWatch is able to evaluate and classify the incoming data in multiple ways, connected to a central station. In the event of a recognized source of fire, it automatically sends out an alarm. FireWatch protects entire eco-systems and cultural landscapes. FireWatch takes care of the economic resources of the endangered areas, was tested successfully and has been commercially installed in Germany, in the states of Brandenburg, Mecklenburg-Western Pomerania, Saxony-Anhalt and Saxony for several years. The technical performance of the system allows the usage in other states and / or countries. PARTICULARS: Tower-based automated reliable early recognition of forest fire Automated detection of smoke clouds by day and night Local online data processing with broadband radio or cable transmission Fast supervision of an area of more then 70,000 hectaresby one sensor High image quality from the beginning of the image pickup right up to the control station's computer FireWatch takes care of the economic resources of the endangered areas, was tested successfully and has been commercially installed in Germany, in the states of Brandenburg, Mecklenburg-Western Pomerania, Saxony-Anhalt and Saxony for several years. The technical performance of the system allows the usage in other states and / or countries. PARTICULARS: Tower-based automated reliable early recognition of forest fire Automated detection of smoke clouds by day and night Local online data processing with broadband radio or cable transmission Fast supervision of an area of more then 70,000 hectaresby one sensor High image quality from the beginning of the image pickup right up to the control station's computer
个人分类: 亥姆霍兹技术转移|5716 次阅读|2 个评论
[转载]prescribed burn的不同看法
hongyuhuang2011 2012-9-18 14:49
http://www.nytimes.com/2012/09/18/science/earth/forest-survey-questions-effect-of-prescribed-burns.html?hpwpagewanted=all September 17, 2012 Forest Fire Research Questions the Wisdom of Prescribed Burns By JIM ROBBINS MISSOULA, Mont. — On a forested mountainside that was charred in a wildfire in 2003, Richard Hutto, a University of Montana ornithologist, plays a recording of a black-backed woodpecker drumming on a tree. The distinctive tattoo goes unanswered until Dr. Hutto is ready to leave. Then, at the top of a tree burned to charcoal, a woodpecker with black feathers, a white breast and a yellow slash on its crown hammers a rhythmic response. “This forest may have burned,” says Dr. Hutto, smiling, “but that doesn’t mean it’s dead. There’s a lot going on.” The black-backed woodpecker’s drum signals more than the return of life to the forest. It also may be an important clue toward resolving a debate about how much, and even whether, to try to prevent large forest fires. Scientists are at loggerheads over whether there is an ecological advantage to thinning forests and using prescribed fire to reduce fuel for subsequent fires — or whether those methods actually diminish ecological processes and biodiversity. The United States Forest Service , which manages nearly 200 million acres of public land, believes limited thinning and burning will prevent catastrophic wildfires. The agency contracts with logging companies to cut down large and small trees across sweeping landscapes, and uses prescribed fire. Besides protecting homes, experts say, these methods also recreate the natural state of the forest. The approach, developed primarily as a result of tree ring studies, seeks to reconstruct the forests of the West before the 20th century, when the large-scale suppression of wildfire first occurred. Some ecologists and environmentalists, however, are challenging the Forest Service’s model, saying it is based on incomplete science and is causing ecological damage. Recent research, they say, shows that nature often caused far more severe fires than tree ring records show. That means the ecology of Western forests depends on fires of varying degrees of severity, including what we think of as catastrophic fires, not just the kinds of low-intensity blazes that current Forest Service policy favors. They say that large fires, far from destroying forests, can be a shot of adrenaline that stimulates biodiversity. The black-backed woodpecker could be an important indicator of which side is correct. The bird lives almost exclusively in severely burned forests. It thrives on the fire-chaser beetle and the jewel beetle, which are adapted to fires and can detect heat 30 miles away with infrared sensors under their legs. Both species lay eggs only in scorched trees whose defenses have been wiped out by fire. The black-backed woodpeckers feast on the beetles’ grubs. Their coloring has evolved to blend in with charred trees so they are not visible to hawks and other predators as they peck away. Tracking the presence of the woodpeckers can indicate whether there are enough severe fires to stimulate their ecosystems, and keep their numbers, as well as those of other species, healthy. William Baker, a fire and landscape ecologist at the University of Wyoming, contends that the kind of limited fires that are being employed to control bigger fires were not as common in nature as has been thought. For a recent paper in the journal Global Ecology and Biogeography, published with Mark Williams, Dr. Baker employed an unorthodox method to reconstruct fire history that challenges current analysis of tree rings. (The study was financed by the National Science Foundation and the United States Department of Agriculture.) Dr. Baker and Dr. Williams examined thousands of handwritten records created by agents of the federal General Land Office who surveyed undeveloped land in the West in the mid-19th century. The surveyors used an ax to mark trees at precise intervals and took meticulous notes on what the vegetation between marked trees looked like — meadow, burned forest or mature trees. Altogether, Dr. Baker’s students combed through 13,000 handwritten records on 28,000 marked trees, and hiked miles in Oregon, Colorado and Arizona to find some of the trees and compare today’s conditions with those from the 1800s. They found that low-intensity fires that occurred naturally were not as widespread as other research holds, and that they did not prevent more severe fires. Dr. Baker concluded that big fires are inevitable, and argues that it is best for ecosystems — and less expensive — to put up with them. “Our research shows that reducing fuels isn’t going to reduce severity much,” he said. “Even if you reduce fuels, you are still going to have severe fires” because of extreme weather. Jennifer Marlon, a paleoecologist at Yale who has studied 3,000 years of fire history in the West, said her work led to a similar conclusion. Compared with the last several thousand years, she said, “fires in the West the last hundred years have been unusually low.” But other fire researchers say they are not yet ready to abandon the current model. “It’s interesting data and needs to be tested,” said Peter M. Brown, a dendrochronologist in Fort Collins, Colo., who studies fire history and consults with the Forest Service. But it’s not nearly enough, he said, to change the current model. Some see support for the argument against prescribed burning in the fading populations of black-backed woodpeckers in California, Oregon and South Dakota. This year four environmental groups filed a petition to have the bird declared endangered, blaming the Forest Service’s policy for the decline. Proponents of the free-fire theory say that while human lives and property should be protected, beyond that widespread wildfires should be viewed as necessary ecological events that reset the clock on a landscape to provide habitats for numerous species for years and even decades to come. This principle stems from research into “disturbance ecology.” For instance, when a hurricane blows down a large swath of forest or a volcano erupts, it strongly stimulates an ecosystem, scientists have found. “Disturbances are very important; they are huge,” said Mark Swanson, a Washington State University ecologist who recently published a paper noting that recovered areas thrived after the eruption of Mount St. Helens in 1980. “You actually have an increase in species richness, sometimes to regionally high levels.” Dr. Hutto, the University of Montana ornithologist, said he believes the Forest Service approach was misguided. He pointed out that morel mushrooms thrive on charred ground, and birds, including the mountain bluebird and black-backed woodpecker, then move in. Similarly, a plant called snowbush can remain dormant in the soil for centuries until heat from a fire cracks its seed coat, and it blooms profusely. “The first year after a fire is when the magic really happens,” Dr. Hutto said.
个人分类: forest fire|2758 次阅读|0 个评论
气候暖化是澳洲林火帮凶
zhangjiahua 2009-2-15 10:21
科学家认为气候暖化是澳洲林火帮凶 来源: 中国气象报社 发布时间: 2009年02月10日   澳洲人虽不是首次面对林火的威胁,但维多利亚州100多人命丧烈火,还是让举国上下无比震惊。科学家表示,澳洲是最易发生火患的大陆,但气候暖化似乎使定期侵害该国的林火火越来越猛。   据澳洲气象局说,澳洲气候干旱,又有含油量丰富的桉树林,意味着林火是该国无可避免的景象之一。澳洲历史上也记载了好几场大型林火,例如1983年导致75人死亡的灰烬星期三,以及1939年造成71人死亡的黑色星期五等。不过,维多利亚州此次的林火,是该国历来最致命的林火,而专家认为,这个问题和气候变化有关。   澳洲林火合作研究中心主任摩尔根说:气候变化、干旱天气,改变了林火的性质、火势和燃烧的时间这个周末的林火,突出了展开科研的重要性,以促进我们对林火各方面影响的理解。   澳洲诗人麦凯勒形容,澳洲是干旱的土地,又是水淹的平原,而悉尼大学林火专家亚当斯也说,有证据显示澳洲的气候越来越动荡不定。   亚当斯说:我从未见过像星期天那样极端的天气和情况,这是前所未有的我们还没有充分的证据,以气候变化来解释这一天发生的事,但至今,所有的科学证据都显示,接下来将会有更多极端的天气包括澳洲南部各个地区将更高温,更干旱。   据澳洲气象局和澳洲科学与工业研究组织预测,随着气候情况的恶化,到了2050年,澳洲南部林火燃烧的天数,可能比现在多出一倍。   另外,澳洲南部林火狂烧,北部却面对严重洪灾。环保团体绿色和平组织表示,如果气候变化持续下去,类似这样的情况将更为普遍。 (消息来源:联合早报网 责任编辑:颜昕)
个人分类: 生活点滴|3419 次阅读|2 个评论

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