Why can you smell rain before it arrives?

Have you ever walked outside on a hot day and suddenly caught that familiar earthy smell in the air?

There is some science behind that familiar experience. Rain itself does not have a smell.

Instead, the scent comes mainly from the ground and becomes noticeable when moisture and raindrops release certain compounds into the air.

That earthy smell of rain has a name

Scientists call the smell petrichor.

Australian researchers Isabel Joy Bear and Richard Thomas introduced the term in the 1960s after studying the smell that comes from dry ground when rain arrives.

People often describe petrichor as earthy, fresh or slightly musky. It becomes particularly noticeable when rain follows a long spell of hot, dry weather.

Where does the smell come from?

Soil plays a big part in creating the smell.

Tiny microorganisms known as actinobacteria live in the ground. They break down dead and decaying material in the soil and, in the process, produce a compound called geosmin.

Geosmin produces a strong earthy smell, and the human nose can detect it even when only tiny amounts are present in the air.

Plants also contribute to petrichor. During dry periods, oils and other compounds from plants can collect on the ground and mix with the other substances that create the familiar smell.

Can you really smell rain before it arrives?

Rain may already be falling somewhere nearby while your area remains dry. Wind can carry geosmin and other compounds released by those raindrops ahead of the approaching rain.

This means your nose may pick up the smell before the first drops reach you.

Changes in moisture before rainfall may also make the earthy scent more noticeable.

So when someone says they can “smell rain coming”, they may actually be detecting compounds carried through the air by the approaching weather.

Where does the smell go after the rain?

As the rain moves away and the ground begins to dry, fewer of these compounds become airborne and the familiar scent gradually fades.

The microorganisms remain in the soil, however, and the process can happen again when dry conditions give way to another spell of rain.

So the next time you step outside and think you can smell rain coming, your nose may be picking up a real change in your surroundings even before the first raindrop falls.