The Moon’s Influence on Rainfall: A Closer Look

Elizabeth Borneman

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We’ve all heard the stories about full moons making people act a bit crazy. Some theories say that this is because the moon has such a strong effect on the water here on Earth, including the water that is inside the human body. Whether or not you notice changes in your behavior when the moon is full or not, the effects the moon has on life here on planet Earth can be dramatic.

How the Moon Influences Rainfall

For instance, the moon affects rainfall in a few different ways. When the moon rises it creates a ‘bulge’ in the Earth’s atmosphere which can influence how much rain is able to fall to the ground. This effect is usually very slight, but even small fluctuations in rainfall can alter the ecosystem of the land far below the moon.

Research on the Moon’s Impact

Atmospheric studies research students are exploring how much of an affect the moon has on rainfall around the world. They are currently chasing atmospheric pressure oscillations which can help them find where is best to collect the data they need. This information has allowed them to create a map of certain areas showing how the moon has changed the levels of rainfall as it waxes and wanes.

View of the Moon transiting the Earth on July 16, 2015.
View of the Moon transiting the Earth on July 16, 2015. Image: NASA.

Findings from Tropical Regions

Over the tropics the map shows a dip in rainfall when the moon is directly overhead. The researchers compiled other supporting data on the phenomena which includes air pressure, rate of change in air pressure as related to the moon’s position in the sky, and rainfall differences over time.


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The moon’s effect on air pressure has been documented since about 1845, but recent a paper by the University of Washington have discussed the additional influence of the moon’s effect on rainfall. The studies showed that when the moon is overhead Earth’s atmosphere moves toward it, causing higher pressure and temperature increases which discourages rainfall down below.

Satellite data over the tropics, between 10 degrees S and 10 degrees N, shows a slight dip in rainfall when the moon is directly overhead or underfoot. The top panel shows the air pressure, the middle shows the rate of change in air pressure, and the bottom shows the rainfall difference from the average. The change is 0.78 micrometers, or less than one ten thousandth of an inch, per hour.
Satellite data over the tropics, between 10 degrees S and 10 degrees N, shows a slight dip in rainfall when the moon is directly overhead or underfoot. The top panel shows the air pressure, the middle shows the rate of change in air pressure, and the bottom shows the rainfall difference from the average. The change is 0.78 micrometers, or less than one ten thousandth of an inch, per hour. From: Kohyama and Wallace, 2016.

References

Kohyama, T., and J. M. Wallace (2016), Rainfall variations induced by the lunar gravitational atmospheric tide and their implications for the relationship between tropical rainfall and humidity, Geophys. Res. Lett., 43, doi:10.1002/2015GL067342.

Moon’s tidal forces affect amount of rainfall on Earth, University of Washington Today, January 29, 2106.

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About the author
Elizabeth Borneman
My name is Elizabeth Borneman and I am a freelance writer, reader, and coffee drinker. I live on a small island in Alaska, which gives me plenty of time to fish, hike, kayak, and be inspired by nature. I enjoy writing about the natural world and find lots of ways to flex my creative muscles on the beach, in the forest, or down at the local coffee shop.