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为什么大多数的雨没有落到地面 – 译学馆
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为什么大多数的雨没有落到地面

Why Most Rain Never Reaches The Ground

你们好 我是《一分钟地球》的凯特
Hi, this is Kate from MinuteEarth.
大部分雨水都不会落到地面上
Most rain never reaches the ground.
因为它们会融入海洋里
Because it falls on the oceans!
但即使有许多雨水落向地面 它们也不会接触到地面
But even a lot of rain that falls over lands doesn’t reach the ground.
有一些雨水在它们还没到地面之前就消失了
Some of it disappears before it gets very far.
当雨滴落下时 它们会经过越来越温暖的空气
As raindrops fall they pass through warmer and warmer air,
这会使雨滴表面的水分子蒸发得越来越多
Which evaporates more and more water molecules from their surfaces.
我们很难测量出这个过程中水的损失量
Measuring that water loss is tricky;
因为我们不能让雨量计飘浮在不同高度
we can’t levitate rain gauges at different heights in the sky.
来直接测量到底蒸发了多少雨量
To directly measure how much rain evaporates,
但计算机模拟结果表明 落下的雨水中大概有40%会返还到空中
But computer simulations suggest that about 40% of falling rain disappears back into the sky.
当雨水最后落到陆地上 大部分也是落在地球的森林里
And when rain does touch down, it lands mostly on Earth’s forests.
那是因为在那些降水丰富的地方
That’s because wherever lots of rain falls,
缺水的树木总会长得高耸粗壮 以遮住其他大部分植物 来取得获取雨水的优势
Thirsty trees dominate by growing tall and wide and shading out most other plants.
那些大叶树冠也碰巧阻截了几乎所有落向其他植物的雨水
Those big leafy canopies also happen to intercept almost all of the rain that falls on them.
然而 就像人类不能通过皮肤来喝水一样
However, just as people can’t drink through their skin,
树也不能通过叶子或树皮来吸收水分
Trees can’t absorb water through their leaves or bark,
所以它们不能直接使用那些被阻截的水分
so the intercepted water isn’t directly of use to them.
大多数雨水或顺着叶子向下滴 或顺着树干往下流
Most of it drips off or runs down their trunks,
最后到达地面 这样树才能用树根来吸收水分
Eventually reaching the ground, where the trees can suck it up with their roots.
但树梢的一些水分也会从树叶和树皮上蒸发
But some of the treetop water also evaporates off of the leaves and bark,
大概有15%原先离开了云层的雨水会回到空中
Returning about 15 percent of the rain that originally left the clouds back up into the sky.
单听这个数字你可能觉得不多
That, alone, might not sound like a lot,
但和之前在下落途中所蒸发的雨水量结合起来
But when combined with the raindrops that evaporated on the way down,
那就意味着有超过一半落向地面的雨水根本不会到达地面
It means that more than half of the rain that falls over Earth’s land never reaches the ground.
而是以水蒸气的方式蒸发回空中
That immense amount of water instead flows back upwards as vapor,
相当于有十五条亚马逊河于无形中爬回天空
the equivalent of 15 Amazon rivers climbing, invisibly, through the sky.
感谢佐治亚南方大学赞助此视频
Thanks to Georgia Southern University for sponsoring this video,
获国家科学基金会资助的约翰·范斯坦使此视频的播出成为可能
which was made possible by a National Science Foundation grant to John Van Stan.
范斯坦是佐治亚南方大学地理学和地质学系的一名教授
Van Stan is a professor in GSU’s Department of Geology & Geography,
他还研究不同的树木是怎么获取落在它们身上的雨水的
and he studies how well different trees capture rain that falls on them.
范斯坦的团队及其合作者的研究
Research from his group and its collaborators
帮助我们理解树木获取雨水能力的重要性
has helped us understand the vital importance of these rain-catching abilities,
包括它们能在倾盆大雨时减少洪水带来的危害
including the way they reduce storm water flooding during heavy downpours,
因此每年为我们节省了数以亿计美元的洪灾损失
thus saving us billions of dollars a year in flooding damage.
感谢佐治亚南方大学
Thanks Georgia Southern!

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在此视频中,你可以了解到多数雨水落不到地面的原因。

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视频来源

https://www.youtube.com/watch?v=1xQ0Ypp3r_8

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