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What is humidity? |
Weather
If someone says that it’s very humid outside, that person means there’s a lot of water vapor in the air. When you go outside it probably feels very damp and hot too! It could even feel tropical, like a rainforest! The reason it’s damp is because of all the water vapor in the air. Also, normally when we sweat, the sweat evaporates into the air and cools us down, but on very humid days, the air is already holding a lot of water. It doesn’t have room for very much more. Our sweat doesn’t evaporate as easily and we feel very hot!
Low humidity can be uncomfortable too. It might feel very dry outside. Without water in the air plants can have a very hard time growing. Cacti (cactuses) are often the only plants in the desert because they are the best at surviving without much water. Low humidity also makes it very easy for fires to start, which can be very dangerous.
People are usually comfortable with a little bit of humidity, but not too much!
Relative Humidity
A lot of times, when people talk about humidity, they refer to the relative humidity. This is a comparison of how much water is in the air to how much water the air can possibly hold. When you see the weather report on TV, the relative humidity is shown by using percentages. If the weather report shows the humidity at 50%, it means the air is holding half as much water as it possibly could.
What do you think it means when the humidity is at 100%? If the air needs to let go of some of its water, what might happen?
Weather Watch
Every day on the news or in the newspaper, the relative humidity is shown with the weather forecast. Take a look at these numbers every day for a week. Each day, when you’re outside, think about how the air feels. How does the humidity affect the air? Is it more likely to rain on days with high or low humidity? At the end of the week, go back and think about which day’s humidity was the most comfortable for you. What kinds of fun things can you do outside on days like that?