In late August 2005, Hurricane Katrina was moving its way across the Gulf coast.
2005年八月底，卡特里娜飓风逐渐向海湾沿岸地区移
It was classified as a Category 3 storm.
卡特里娜飓风被定位为三级飓风
Dangerous, but in a region with a long history of Category 4 and 5 hurricanes,
它固然危险，但在一个长期遭受四级飓风和五季飓风的地区，
it wasn’t expected to be the most intense.
卡特里娜飓风并未被当做最剧烈的风暴潮
Katrina was only one day away from the Louisiana coast
卡特里娜飓风才离开路易斯安那海岸一天
when the mayor of New Orleans issued an evacuation order.
新奥尔良市长就发布了撤离命令
Unfortunately, it was too late.
不幸的是，已经晚了
The sea level had already risen in a phenomenon called storm surge.
新奥尔良海平面的上升幅度已经达到了风暴潮级别
Water rapidly rose up against the city's levees,
海水迅速漫过了堤坝
a series of walls designed to keep the area from flooding.
也就是修来抵御洪水的一系列墙体
Before Katrina made landfall, the levees broke.
卡特里娜飓风尚未着陆，堤坝就已被冲毁
A wall of water rushed into the city, trapping thousands.
一堵水墙涌入城市，成千上万人因此被困
What followed was one of the worst natural disasters in US history.
接下来，美国爆发了历史上最严重的自然灾害
We're expecting storm surge of 20 to 30 feet high
据悉，因为卡特里娜飓风引起的风暴潮，水位将上涨20-30英尺
Flood waters are drenching city streets
洪水淹没了城市的街道
A levee broke during the height of the storm
洪水又冲断了一条堤坝
There are bodies...uh...floating in the water there.
有……尸体……浮出水面
Storm surge was the main cause of death during Hurricane Katrina.
卡特里娜飓风期间，风暴潮是导致死亡的主要原因
In fact it can be the most dangerous part of any hurricane.
事实上，对任何一场飓风而言，风暴潮都可能是最危险的因素
It occurs when strong winds from an approaching hurricane push water into the shore.
飓风临近时带来的强风将水压入海岸内，风暴潮就此形成
As the sea rises, a bulge of water sweeps over coastal areas,
随着海平面上升，一股洪水席卷了沿岸地区
causing destruction along the way.
所到之处，一片狼藉
These are the normal astronomical tides at Dauphin Island to the east of New Orleans.
新奥尔良以东的多芬岛平时的浪高是这样
When you compare them to the water levels during hurricane Katrina —
当你将其与卡特里娜飓风时期的水位相比
you can see the dramatic rise.
就能看出卡特里娜飓风期间水位上涨了多少
That’s the storm surge.
这就是风暴潮
What makes this rise dangerous
这一水位上涨之所以危险
is that it starts to build up before the hurricane makes landfall
是因为飓风还未着陆它就已经开始形成了
So the coastal flooding from it
所以，风暴潮会给沿海地区带来洪水
can make evacuation procedures and the impact of a hurricane much worse.
撤离为此变得更加困难，飓风的危害也为此变得更加严重
In 2008, hurricane Ike caused a big storm surge around Galveston, TX a day before landfall.
2008年，艾克飓风着陆前一天，德克萨斯的加尔维斯敦地区就出现了巨大的风暴潮

The rising water cut off evacuation routes, stranding hundreds.
水位上升阻断了人们撤离的路线，成百上千人受困
More recently, the National Hurricane Center issued dire warnings for the storm surge accompanying Hurricane Irma,
不久前，国家飓风中心发布了艾尔玛飓风及随之而来的风暴潮紧急警告
the most powerful storm to ever rage through the Atlantic Ocean.
这一飓风是大西洋一带遭遇的最强风暴潮
A storm surge can also be unpredictable.
风暴潮有时也是无法预测的
Rising sea levels caused by global warming increase the risk of storm surge.
全球变暖导致的海平面上升使得风暴潮来袭的可能性变得更大了
But there are many factors that can change its size and strength.
然而，风暴潮的大小和强度会受很多因素的影响
For example, the largest one recorded before Katrina was about 22 feet,
例如，卡特里娜飓风之前风暴潮最高纪录是水位上涨22英尺
during Hurricane Camille in 1969.
那一次是1969年的卡米拉飓风
But Camille was a category 5 storm with 190 mph winds.
但卡米拉飓风是五级飓风，风暴潮速度为每小时190英里
Katrina was only a category 3 with 130 mph winds,
卡特里娜飓风仅仅是风速为130英里每小时的三级风暴潮
but it had a storm surge of about 28 feet
但卡特里娜飓风使得水位上涨了28英尺
Katrina had slower winds than Camille
卡特里娜飓风的风速低于卡米拉飓风
but it was twice as wide, which dramatically increased the storm surge.
但它的宽度是卡米拉飓风的两倍，从而使得风暴潮的强度大大增加
In addition to wind speeds, meteorologist predict storm surge by taking into account
除了风速，气象学家在预测风暴潮时还要考虑
the size of the storm, it's direction, angle of approach, and shape and depth of the coast.
风暴潮的大小，方向，着陆的角度，当地海岸的形状和深度等因素
These calculations help forecasters warn communities at risk.
这些计算使得风暴潮预测者们能够及时提醒有风险的地区
But they’re often not enough to prevent damage on the ground.
但仅仅靠这些计算，是不足以预防岸上的损失的
This map shows the highest storm surge events worldwide since 1880.
这张地图标出了1880年以来世界上出现过的最高上涨水位
In the US, the eastern and southeastern coastlines
就美国而言，东部海岸和东南海岸
are among the most vulnerable areas for storm surges in the world.
是世界上最容易受到风暴潮影响的地区之一
Along the east coast, hurricane Sandy got its strength from a massive storm surge in 2012.
在东部海岸，2012年桑迪飓风就带来了大规模的风暴潮
On the Gulf Coast side, places like Texas and South Florida have seen multiple hurricanes
海湾沿海的德克萨斯和弗罗里达南部也经历了多次飓风
so they've built infrastructure to help defend against excessive flooding.
所以他们建成了一些基础设施，抵御洪水泛滥
Levees and seawalls are designed to stop or redirect rising water away from cities.
修建了堤坝和海堤，阻止洪水涌入城市，并将洪水从城市里引流到其他地方
But even those can be inadequate,
但这些措施还是不够
as seen during hurricanes Katrina and more recently, Harvey.
卡特里娜飓风以及前不久的哈维飓风都证明了这一点
What really concerns experts, though,
然而，专家们真正担心的是
are places that don’t experience a lot of hurricanes but are still vulnerable to storm surge.
那些没有经历过飓风但很有可能会遭受飓风的地区
This map shows that in the event of a big hurricane,
这张地图显示，大型飓风来临时
the coasts of Northwest Florida and Georgia would be at comparable risk to the Gulf Coast.
在弗罗里达西北海岸和佐治亚海岸着陆和在海湾地区着陆的可能性一样大
These areas have shallow water,
这些地区的海水很浅
which means sea level can rise faster and water can reach further inland
也就意味着海平面上涨的速度会更快，登陆后海水能到达更远的地方
making the flooding worse.
引发的洪水也会更大
But they’ve seen fewer hurricanes than the Gulf Coast and they are likely to be less prepared.
然而，这些地区并不像海湾地区经历的洪水那么多，因而会更加缺乏准备
So when a major hurricane like Irma hits low-lying areas like these,
所以，要是艾尔玛飓风那样的大飓风袭击这种低地地区
the storm surge can be the first and deadliest thing headed their way.
这里将会是风暴潮沿途最先登陆也是损失最为惨重的地方