洛杉矶的下一个威胁是什么？降雨可能导致山体滑坡
【中美创新时报2025 年 1 月 17 日编译讯】（记者温友平编译）山体滑坡的可能性只是洛杉矶居民在大火最终被扑灭后将面临的威胁之一，专家警告说，这一过程可能需要数周时间。《纽约时报》记者Austyn Gaffney对此作了下述报道。
当风和火焰继续肆虐洛杉矶时，小队开始爬上它们留下的烧焦的土壤。
大约十几名加州流域应急小组和美国森林服务局的成员正在研究伊顿和帕利塞兹大火的边缘，以确定哪些土地烧得最严重。很快，他们将发布灾害地图，帮助人们为接下来发生的事情做好准备：在城市恢复期间，几乎肯定会发生洪水和山体滑坡，这些威胁将持续数天、数月甚至数年。
“野火过后，公众面临的危险还没有结束，”加州地质学家杰里米·兰开斯特说。他和他的团队周三在圣盖博山和圣莫尼卡山两侧的陡峭峡谷徒步旅行。当雨下得足够大时，这些斜坡上的沉积物会迅速滚落到越来越靠近火灾多发山麓的房屋上。
山体滑坡的可能性只是洛杉矶居民在大火最终被扑灭后将面临的威胁之一，专家警告说，这一过程可能需要数周时间。
随着数千名居民因火灾而流离失所，长期存在的住房和无家可归危机将加剧。此外，几个社区的供水也受到影响。
洛杉矶水电局和洛杉矶县部分地区已向帕利塞兹、阿尔塔迪纳和邻近社区的居民发出“请勿饮用”和“请勿煮沸”的通知。侵入城市的野火可能会将有害化学物质（也称为挥发性有机化合物）引入市政供水系统。
专家表示，公用事业公司需要数周时间才能确定污染程度，而补救措施则需要数月时间。在此之前，在这些地区饮用、洗澡或使用自来水可能会带来难以言喻的健康后果。
为了缓解住房问题，州长加文·纽瑟姆周四签署了一项行政命令，旨在加快临时住房的建设。
纽瑟姆在一份声明中表示：“今天，我们正在通过移除路障和加强对剥削的保护来加快建造新的临时住房。”
州长办公室表示，这项举措将放宽对移动房屋和临时住房的限制，部分原因是允许紧急机构更容易在被烧毁的地段上建造这些建筑。
该命令还将延长禁止房产卖家、房东和酒店经营者哄抬价格的期限，因为对临时住房的需求引发了竞价战和令人瞠目的房地产价格上涨。纽瑟姆早些时候发布的一项行政命令限制了在野火烧毁的地区未经请求的报价、房地产投机和驱逐。它还规定，只要危机持续，租金涨幅不得超过 10%。
红十字会和其他救灾机构在洛杉矶开设了八个避难所。这些避难所总共可容纳约 800 人。
该地区最大的两场火灾——帕利塞兹和伊顿大火，共摧毁或损坏了 10,000 多座建筑，这暴露了该地区本来就属于美国最负担不起的住房市场之一的不平等现象。
加州总检察长罗布·邦塔 (Rob Bonta) 在一份声明中表示：“整个地区的人们都被贪婪的企业和房东、骗子和掠夺性买家所利用，他们想从痛苦中快速赚钱。我的办公室在此表示，这不仅是错误的，也是非法的。”
洛杉矶地区的房地产经纪人描述了混乱的房屋买卖争抢，以及通过私下网络，未上市的房产可以迅速以数百万美元的价格售出。
在太平洋帕利塞兹社区，家庭年平均收入为 375,000 美元，是城市平均收入的三倍多，帕利塞兹大火导致的流离失所者正在为邻居购买第二套和第三套住房而争相购买。
与此同时，山体滑坡威胁十分严重。山火后的两大主要危害是山洪暴发和火灾后泥石流。虽然海绵状土壤通常会吸收水分，但烧焦的土壤会变得像混凝土一样坚硬，排斥水分。然后，水会顺着山坡流下，火灾后几乎没有植被可以控制水流。
灾害地图结合了卫星图像和土壤实地测试，以显示中度至重度烧焦土壤的斑块可能使这些火灾后风险更有可能发生的地方。地图还附有紧急服务部门设置路障以抵御危险的建议。
虽然洛杉矶地图尚未公布，但专家表示，帕利塞兹火灾的烧伤严重程度大多为低至中等，而伊顿火灾的烧伤严重程度可能为中度至高度。
泥流需要三种因素——陡坡、烧焦的土壤和雨水——而且它们往往比洪水更危险，因为它们吸收的沉积物会侵蚀地表，形成滚雪球效应，卷走树木、植被、土壤、岩石和沿途其他任何东西。
“泥流就像是一场加强版的洪水，”美国地质调查局的研究水文学家 Jason Kean 说。“它充满了岩石、泥浆和树木。”虽然洪水通常影响范围更广，但泥流中的水流速度更快，泥流虽然不太常见，但破坏性更强。
2017 年托马斯大火之后，加利福尼亚州蒙特西托的泥流造成 23 人死亡，400 多所房屋受损或被毁。
房屋保险和联邦洪水保险均不承保泥流对财产的影响，美国地质调查局将泥流定义为山体滑坡。
火灾-洪水周期是一种长期研究的关系，但科学家表示，全球变暖使火灾后威胁更有可能发生。火灾燃烧得更大、更严重。降雨更猛烈、更频繁。这些变化扩大了火灾后危害的目标区域，这可能会增加洪水和泥流的规模和频率。
由于地形非常陡峭、沉积物多、火灾活动频繁以及许多人挤在山上，洛杉矶面临着极大的风险。
“洛杉矶地区和南加州是火灾后泥流的世界之都，”基恩说。
本报告使用了《华盛顿邮报》的材料。
本文最初发表于《纽约时报》。
题图：周四，在加利福尼亚州马里布，人们看到了被帕利塞兹大火摧毁的房屋残骸。Jae C. Hong/美联社
附原英文报道：
The next threat to Los Angeles? Rainfall that could cause landslides.
By Austyn Gaffney New York Times,Updated January 16, 2025
The remains of homes destroyed by the Palisades Fire were seen Thursday in Malibu, Calif. Jae C. Hong/Associated Press
While winds and flames continued to ravage Los Angeles, small teams began creeping onto the charred soils left in their wake.
Roughly a dozen members of the California Watershed Emergency Response Teams and the US Forest Service are studying the edges of the Eaton and Palisades fires to determine what patches of land burned most severely. Soon, they’ll issue hazard maps to help people prepare for what comes next: the near-certain threat of floods and landslides that will loom for days, months, and even years while the city recovers.
“After a wildfire, the hazard to the public is not over,” said Jeremy Lancaster, California’s state geologist. He and his team spent Wednesday hiking in the steep canyons that flank the San Gabriel and Santa Monica mountains. When it rains hard enough, the sediment on slopes such as these can swiftly tumble downhill onto houses that increasingly push up against the fire-prone foothills.
The potential for landslides is just one threat residents of Los Angeles will face after the flames are finally extinguished, a process that experts warn could take weeks.
A long-running crisis over housing and homelessness will intensify with thousands of residents displaced by the fires. Also, water supplies in several neighborhoods have been compromised.
The Los Angeles Department of Water and Power and parts of Los Angeles County have issued “do not drink” and “do not boil” notices to residents in the Palisades, Altadena, and neighboring communities. Wildfires that encroach into cities risk introducing harmful chemicals otherwise known as volatile organic compounds into the municipal water system.
Experts say it will take weeks for utilities to determine the extent of any contamination and months before remediation takes place. Until then, drinking, bathing, or using tap water in these areas could have untold health consequences.
In a bid to alleviate the housing problems, Governor Gavin Newsom on Thursday signed an executive order aimed at expediting the construction of temporary housing.
“Today, we are expediting the creation of new temporary housing by removing roadblocks and strengthening protections against exploitation,” Newsom said in a statement.
The initiative will ease restrictions on mobile homes and temporary housing, in part by allowing emergency agencies to more easily build those structures on burned lots, the governor’s office said.
The order will also extend prohibitions on price gouging by property sellers, landlords, and hotel operators, as the demand for temporary housing has set off bidding wars and eye-watering price increases for real estate. An earlier executive order from Newsom had restricted unsolicited offers, property speculation, and evictions in areas burned by the wildfires. It also capped rental increases to 10 percent for as long as the crisis persists.
Eight shelters have been opened in Los Angeles by the Red Cross and other disaster relief agencies. Together, they can house around 800 people.
As the Palisades and Eaton fires, the two largest in the area, have destroyed or damaged a total of more than 10,000 structures, it has laid bare the inequalities in what was already one of America’s least affordable housing markets.
“Folks across the region are being preyed upon by greedy businesses and landlords, scam artists, and predatory buyers looking to make a quick buck off their pain,” Rob Bonta, California’s attorney general, said in a statement. “My office is here to say this is not only wrong, it is illegal.”
Los Angeles-area real estate agents have described chaotic scrambles to buy and sell homes, and whisper networks through which unlisted properties quickly sell for millions of dollars.
In the Pacific Palisades neighborhood, where the average annual household income of $375,000 is more than three times the city average, residents displaced by the Palisades fire are fighting to buy their neighbors’ second and third homes.
Meanwhile, the landslide threat is pronounced. The two major hazards after a wildfire are flash flooding and postfire debris flows. While spongy soils typically absorb water, burned soils can become hard packed like concrete, repelling water. Water then funnels downslope without much, or any, vegetation left after a fire to keep it in check.
Hazard maps use a combination of satellite images and field testing of soils to show where patches of moderately to severely burned soils could make these postfire risks more likely. Recommendations for emergency services to engineer barricades against the danger accompany the maps.
Although the Los Angeles maps are not public yet, experts said the Palisades fire had mostly low to moderate burn severity, while the Eaton fire was likely to have more moderate to high burn severity.
Debris flows require three ingredients — steep slopes, burned soils, and rain — and they’re often more dangerous than floods because the sediment they draw in claws at the landscape, creating a snowball effect that pulls a tumult of trees, vegetation, soil, rocks, and anything else in its way.
“A debris flow is like a flood on steroids,” said Jason Kean, a research hydrologist with the US Geological Survey. “It’s all bulked up with rocks and mud and trees.” Although floods often have a longer reach, water churns faster in debris flows, which are less common but more destructive.
After the Thomas fire in 2017, a debris flow in Montecito, Calif., killed 23 people and damaged or destroyed more than 400 homes.
Neither homeowners insurance nor federal flood insurance covers the impact to properties of debris flows, which are defined by the USGS as landslides.
The fire-flood cycle is a long-studied relationship, but scientists say a warming planet has made the postfire threat more likely. Fires burn bigger and more severely. Rains hit harder and more often. Those changes expand the target area for postfire hazards, which could increase the size and the frequency of floods and flows.
With a dangerous combination of very steep terrain, lots of sediment, high-fire activity, and a lot of people pushed up against the mountains, Los Angeles faces an extreme risk.
“The Los Angeles area and Southern California are the world capital for postfire debris flows,” Kean said.
Material from The Washington Post was used in this report.
This article originally appeared in The New York Times.
