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Total Amount of Rainfall on the Earth per Year

Every now and then, I’m asked a question that, upon figuring out the answer, staggers my mind. The answer is almost always quite interesting to me, even if it can’t be fully grasped. Such is the case when I was asked about the total rain that fell on the earth every year.

The question actually asked about how many raindrops hit the ground and this part can’t be calculated because raindrops can be tiny or large and there can be many falling or just a few falling in a given storm.

However, the average rainfall on the earth is about 39 inches per year. Naturally, some areas get far more rain per year than others get, so this is merely the average. From this, the volume of rain that falls can be figured out. Are you ready to be blown away at the result?

The formula is actually fairly simple, though it is rounded off. The formula is 4 x pi x the radius of the earth (in meters) squared. The number that results is what is staggering. It is about 5.1 x 10^14 cubic meters.

Put in a way that is a little easier to read, that is 510,000,000,000,000 cubic meters of rain or 510 quadrillion cubic meters per year. It can be taken a step farther.

A cubic meter of water weighs about 2,204.62 pounds or about a metric tonne. This means that around 510 quadrillion metric tonnes of rain fall on the earth every year. I’m really glad that figuring out how many raindrops are in a cubic meter is an impossibility. These numbers are already so big that a person can’t actually grasp them.

Of course, the question had to do with how much hit the ground, so the amount that falls in the ocean would need to be removed from the figure. About 29% of the earth’s surface is covered by land, so the total number would be 29% smaller. It would mean that “only” 147 quadrillion cubic meters (or metric tonnes) of rain falls on land every year.

This was one of the first questions I answered this morning and I hadn’t even finished my first cup of coffee!

  • What do you think about the total amount of rain that falls per year?

    • I’m amazed by the numbers
    • I can’t grasp or visualize the number
    • I don’t find this interesting

What do you think?

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Written by Rex Trulove

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13 Comments

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    • Yes, it is a difficult calculation. What makes it a little easier is the fact that when it is hot and dry in one place, it is almost always cool and wet in another, so on a global scale, it evens out. Globally, the amount of rain doesn’t change a great deal, so it can be figured out, even though some places might be experiencing droughts.

        • It is common for people to also not think about the fact that rainfall amounts in one state can drastically affect the water tables in other states that are quite a way distant. There is still some flooding going on in some places and it is boosting the aquifers in places that are sweltering. The snow we get in Montana in the winter increases water tables in states that are hundreds of miles away, literally.

          The best news for us here in Montana is that our fire danger is still only moderate. Two years ago, when we had a terrible forest fire year, fire season began in the first week of June. Fire season begins when the fire hazard reaches extreme.

          • They have a fire in the Everglades right now which surprises me; but it’s been very dry in Florida which is unusual. I didn’t realize that water tables were affected so far away. Thank you for this information, Rex.

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