Why Rain Changes Smell With The Seasons

Chances are, you’ve stepped outside as the first drops of a spring or summer rain begin to fall and noticed the strong aroma. Yes, there is a particular scent that comes along with rain, but did you know that the season can determine what that scent smells like?

Yes, rain in different seasons comes with different scents.

What may surprise you is that it’s not really the rain you are smelling, but the chemical cocktail of what’s happening to the plants and soils around you. And that recipe changes depending on the season.

A Rainy Day’s Signature Scent

The aroma most people recognize has a name: petrichor. This was coined in 1964 by two Australian researchers, and the term describes the earthy fragrance released when rain falls on dry ground.

Let’s break down the chemistry behind the three main sources that give rain its unmistakable smell.

Geosmin: an organic compound produced by a certain bacteria living in the soil, called Streptomyce. Human noses are extraordinarily sensitive to it, and it’s thought that we are more attuned to it than sharks are to blood.

Plant Oils: a blend of plant oils accumulates on rocks and soil during dry stretches. When raindrops strike the ground, they trap tiny air bubbles that burst upward, flinging these compounds into the air as aerosols. MIT researchers captured high-speed video of this in 2015.

Ozone: the sharp, almost metallic smell that often arrives before a storm. Lightning splits oxygen molecules in the atmosphere, and downdrafts carry the resulting ozone to ground level, giving thunderstorms their distinctive pre-rain smell that’s so recognizable.

These three combined give us the petrichor scent, or as I’m calling it, rain’s signature scent. However, depending on the season, this scent can change.

Different Seasons Equal Different Recipes

Spring/Summer: Rain’s scent is most intense in the spring and summer months. Just as the heat and humidity can make us smell, it does the same to rain. That heat and humidity allow for an increase of geosmin, which is the smell we are so sensitive to.

Autumn: As leaves fall and begin to decompose, fungal life begins to flourish. This can change the scent of rain to a more earthy smell. It’s not as strong as the summer scent and can many times appear more musty. Much of this is due to the tannins and other organics that are released when the drops hit the decomposing foliage.

Winter: The winter months bring the most bland scent of all. Plants are dormant, and soil bacteria are much less active, therefore reducing the amount of oils and compounds released. Another factor could be that our olfactory system itself becomes less sensitive in the cold, which could mask some of the scent being released.

And it’s not just the seasons that can dictate the scent of rain, but location as well. Across drier climates in the U.S., such as Arizona and New Mexico, rain can have a stronger smell. This is because rain smells strongest after dry spells, which these areas are more likely to have.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.