Water is an essential building block to life and it comes to us from above.

水是生命重要的組成成分，從天而降來到我們身邊。

Rainwater fills streams, rivers, and lakes.

雨水充斥著溪流、河道及湖泊。

It carries with it the potential for life to flourish.

水帶來生命蓬勃發展的可能。

It can turn an arid desert in to an oasis; convert a stream to white water rapids in the monsoon season, and breathe life into the harshest places on earth.

可以將乾旱沙漠變成綠洲，將小溪變成季風雨林的激流，為地球上最嚴酷的地方注入生命力。

So how do clouds form to keep giving us the essential H2O we need?

那麼，雲是如何形成的？又如何持續提供我們水這項基本所需的？

That's what we'll find out today, in this episode of The Infographics Show: Why Does It Rain?

今天本期《資訊圖表秀》帶您了解：為什麼會下雨？

Clouds are possibly the most interesting and beautiful of all weather phenomena.

雲可能是所有天氣現象中最有趣、美麗的。

They form in a wide variety of shapes and sizes, but are all made of the same thing...water.

雲有各式各樣的形狀和大小，但都是水組成的。

Though we may not notice it, almost all the air around us is moist because it contains water in the form of vapor.

雖然可能沒有察覺，但我們周遭的空氣幾乎都是潮溼的，水分以水蒸氣形式存在空中。

You can't see the water vapor, because it's a gas, but it is still there.

雖然水蒸氣是種氣體，我們看不到，但它仍然存在。

Water can be either solid as ice, liquid as water, or gas, which is a vapor.

水的形式有幾種，固態的冰，液態的水，還有氣態的蒸汽。

Vapor has no smell and it's invisible.

蒸汽無色無味。

But you can feel it.

但可以感覺到。

Imagine a hot and sticky day in summer, or a cold foggy day in winter.

想象夏天炎熱粘稠的日子，或是冬天寒冷起霧的一天。

Those sensations are water vapor.

這些感覺都是水蒸氣造成的。

If you put steam or vapor under the microscope, you would see millions of tiny water droplets floating in the air.

如果將蒸汽放在顯微鏡下，會看到數以百計的小水滴漂浮在空中。

This is the same process that forms clouds - millions of tiny water droplets condensing out of the air to form liquid water.

這也是形成雲層的過程，空氣中數以百計的小水滴凝結在一起，形成液態水。

But why does water condense out of air and become visible as a cloud?

但為什麼水會從空氣中凝結出來，變成可見的雲呢？

Warm air holds water vapor better than cool air, so when warm air starts to cool, it can no longer hold as much of the vapor.

比起冷空氣，溫暖的空氣能容納更多水份，因此暖空氣開始冷卻時，就無法容納那麼多水氣。

The extra water vapor has to go somewhere.

但多出來的水蒸氣總得有個地方待。

It condenses out as water.

它們會以水的形式凝結出來。

To see this in action, go outside and stare up at a cloud.

想親眼見證這一過程，請到室外，盯著雲朵看。

Be patient but keep watching the cloud, especially it's edges.

要有耐心，持續觀察雲朵，特別是它的邊緣。

You will see the edges change, either growing larger or getting smaller.

你會看到邊緣變化，要麼變大，要麼變小。

This is cloud formation in action.

這就是雲層形成過程。

The cloud grows because more of those water droplets are condensing out of the air.

雲變大是因為更多水份從空氣中凝結。

And when it shrinks, you are seeing the droplets evaporating, or changing from visible liquid water into invisible water vapor.

而雲縮小時，你看到的是水份蒸發，或是說從可見的水滴變成不可見的水蒸氣。

But not every cloud has rain pouring out of it.

但不是每朵雲都會下雨。

So, how does the formation of a cloud become actual rain?

那麼，雲是如何下雨的呢？

For rain to be produced, the water condensing in the clouds has to become so heavy that it will fall to Earth,

要想產生雨水，雲中凝結的水必須夠重，到會將水到地面的程度。

or else the tiny droplets will just stay suspended in the cloud, in the same way we see fog just hang there.

否則這些小水滴就會一直懸浮於雲層中，與霧氣一樣留在空氣中。

To become heavier, the droplets need to grow into drops, and to do this, they have to acquire more water and become larger.

為了變得更重，小水滴需要增長為水滴，為了達到這點，雲必須獲得更多的水份，變得更大。

As the droplets collide with each other, some will combine and become larger,

水滴相互碰撞時，有些會結合變得更大，

and others will grow as more water condenses out the air directly into the droplet, until they become condensed and heavy enough to fall to the earth as rain.

而其他水滴則隨著更多的水從空氣中直接凝結到液滴中，液滴會越來越多，直到重到足以作為雨滴降水到地面。

Or if the weather is very cold, the tiny droplets freeze and fall down as snow, hail, or sleet.

或如果天氣非常寒冷，小水滴會凍結，並以雪、冰雹或雨夾雪的形式落下。

So, there you go – that's what a cloud is, and how it creates rain.

現在你知道了，這就是雲是什麼，以及降雨的過程。

But what causes the air to cool in the first place?

但最初是什麼導致空氣冷卻呢？

We mentioned earlier, that cooling the air reduces its ability to hold water, and triggers the formation of water droplets.

之前提到過，空氣冷卻會降低其持水能力，並形成水滴。

To create clouds, and to have rain, the air has to be cooled.

要產生雲跟雨，空氣必須先冷卻。

Most of the science journals we looked at state that there are three main ways in which this happens.

我們查看的大多數科學期刊都指出，降雨主要有三種情況。

These are known as relief rain, frontal rain, and convectional rain.

分別為地形雨、鋒面雨和對流雨。

Let's take a look at how each of these work.

讓我們來看看這三者是如何運作的。

Relief rain, sometimes referred to as orographic rain, is caused when air is forced to cool as it rises over a physical obstruction, such as a mountain range, or big hills.

地形雨會在空氣被強制冷卻時產生，而雲越過物理障礙物，如山脈或大山時，就會上升。

As the warm air rises over the obstruction, it cools, and clouds form.

暖空氣上升到障礙物上方時，就會冷卻並形成雲層。

Relief rain is common in mountainous areas where it can lead to more extreme local rainfall patterns, because the rain clouds form very quickly.

地形雨在山區很常見，其雨雲形成非常迅速，因此可能導致極端局部降雨。

Often one side of a mountain is warm and sunny, and the other side, only a few hundred feet away, is wet and rainy.

時常會有山的一邊溫暖且陽光充足，但幾百英尺外的另一頭卻潮溼，多雨的情況。

Frontal rain develops when two bodies of air, an area of warm air and an area of cool air, meet.

當兩個氣團（暖空氣及冷空氣）相遇，就會形成鋒面雨。

The colder air mass is heavier than the warmer air, and so the lighter, warmer air rises over the top of the heavier, cooler air.

較冷的氣團會比暖氣團重，所以較輕、較暖的氣團會升到較重、較冷的氣團上面。

As the warmer air rises over the cold air it also starts to cool, condensation occurs, and the cloud forming process begins, leading to rain.

暖空氣上升到冷空氣上方時，它也會開始冷卻凝結，雲開始形成，導致下雨。

Where frontal rain develops, skies are typically grey and mostly covered by clouds.

鋒面雨形成的地方，天空通常是灰色的，且大面積被雲層覆蓋。

And finally convectional rain.

最後是對流雨。

On a warm day, the sunshine heats up the ground, and the air above is also warmed, causing it to expand and rise.

在溫暖的日子裡，陽光加熱地面，在那之上的空氣也被加熱，導致其膨脹上升。

As it continues to warm, it absorbs more water because, as we mentioned before, warm air can hold more water than cool air.

繼續變暖時，空氣會吸收更多的水份，正如我們之前提到的，暖空氣能比冷空氣容納更多水份。

But as it rises, the temperature starts to drop again, because the atmosphere gets cooler as you go higher - by roughly one degree centigrade for every 100m of altitude.

但當空氣上升，溫度又開始下降，因為海拔越高大氣層越冷，每升高 100 米，就會降溫約 1 攝氏度。

When the air reaches a height where the temperature forces the water vapor to start condensing, clouds begin to form.

當空氣達到一定高度，溫度迫使水蒸氣開始凝結，雲層就開始形成。

Clouds formed this way are called cumulus clouds, or cumulonimbus clouds, and they usually lead to very heavy rain, often with thunder and lightning.

以這種方式形成的雲被稱為積雲或積雨雲，通常導致大雨，伴隨閃電。

Convectional rain is experienced at the end of a hot summer day, like when the air feels heavy and we can tell a storm is brewing.

對流雨會在炎熱夏日中一天快結束時出現，當空氣變得沉重，可以感覺到一場風暴正在醞釀。

So, that's the process of clouds forming.

那麼，這就是雲的形成過程。

Clouds cool the Earth's surface by reflecting sunlight, and they supply water that is essential for the survival of plants, animals, and us humans.

雲層通過反射太陽光來冷卻地球表面，而且對動植物和人類生存來說，雲層供給的水份必不可少。

Have you experienced extreme or severe rain, when the water we need turns from friend to foe?

你是否經歷過從滋養人類變為迫害人類的極端降雨呢？

Describe the worst storm you've ever been in, in the comments below.

請在下方留言跟大家分享經歷過最糟的風雨。

Also, be sure to check out our other video called What Is Life Like In The Smallest Country In The World?

也別忘了看看我們的另一支影片《世上最小國家的生活》。

Thanks for watching, and, as always, don't forget to like, share, and subscribe.

感謝收看，一如既往，不要忘記按讚、分享和訂閱。

See you next time!

下次見！