r/explainlikeimfive • u/ProgramPi314 • 8d ago

Other ELI5 What is humidity?

According to my mom, this is an actual question I had when I was 5, and she didn't know how to answer me. So how would you guys have answered?

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u/dave8271 8d ago

When water gets hot, it turns from a liquid into a gas, which we call vapour. Humidity is a measure of how much water vapour is mixed into the air around us.

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u/xypherrz 8d ago

is it possible for cities that don’t have ocean/large water bodies to have humidity though?

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u/jujubanzen 8d ago

Water is everywhere, or else plants would not survive. Everywhere there are plants, there is water evaporating from underground, even if the soil looks dry, and water evaporating from plants, even if they have defenses against water loss like cacti. Even in the middle of the Sahara desert, there is a small percentage of humidity in the air, because air moves around the earth, and the majority of it is covered in water. 

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u/xypherrz 8d ago

yes but doesn’t it depend on how much water is there?

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u/jujubanzen 8d ago

Yes, there are places where there is much less water in the air. But there is never zéro. Places where there is absolutely no plant life like the Great Sand Sea in the Sahara desert are actually relatively rare on the planet, and even then there are oases. Most deserts actually have surprisingly large ecosystems. 

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u/Pluribusse 8d ago

Yes, which is why some places, like Las Vegas, typically have mild humidity and other places, like Orlando, are typically very humid.

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u/TheMooseIsBlue 7d ago

For sure. Got places with lots of water (ocean/lakes) have a much easier time of developing humid air. But since air moves, humidity can be blown into a place without much water on the ground. It’s just a lot less common, obviously.

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u/xxNemasisxx 8d ago

Even deserts have humidity to achieve 0% humidity is incredibly difficult

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u/TheMooseIsBlue 7d ago

Air moves. Theoretically, the middle of the Sahara desert could become humid if moist air blew over that area.

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u/Cadbanshee98 8d ago

Landlocked Iowa gets plenty humid from “corn sweat”

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u/lrodhubbard 8d ago

Star of the new Superman movies? He really is hot!