As a ranger, I often encourage guests to use all of their senses whilst on safari. Not only is it important to admire the beauty of the bushveld through one’s eyes, but in my opinion, it’s important to engage more than just our sense of sight. Often after a long, dry winter, the arrival of the first summer rains bring much delight, not only to the animals but ourselves as well. The rainfall has brought more birdsong for us to listen to, it has filled our rivers, allowing us to take off our shoes and feel the water run past, and last but not least it has allowed us to smell a plethora of aromas.
The early summer rains have brought with them an abundance of insects. As a result, many of the migratory birds such as Woodland Kingfishers have returned with their loud, trilling ‘kri-trrrrr’ as an iconic bird call for all to listen to from October through to April
Picture this, it’s a warm, dry day and we are in the early stages of the rainy season. There is an immense cloud build-up over the Drakensberg Mountain Range and you can see a blanket of rain coming towards you. You can smell it before you see it, can’t you? Most of you reading this article will know what I’m talking about when I describe that beautiful aroma that one smells when raindrops hit dry earth. That fresh, musky scent fills our nasal passages when raindrops make landfall and bring relief to barren soil or a hot tar road. Don’t let the title of this article mislead you, the rain itself has no scent, it is rather the moistening of the soil that speeds up the breaking down of dead or decaying matter by a group of bacteria, causing a certain compound to be released into the atmosphere that we smell.
A berg wind that comes off of the Drakensberg mountain is often a predecessor to a big thunderstorm in the Lowveld regions. It is a hot, dry wind that blows down the inland escarpment from the high central plateau towards the coast.
Elaborating slightly further on the process without making it too complicated, the pleasant smell is attributed to a group of actinobacteria, more specifically Streptomyces, which is present all over the ground and in most soils. The earthy odour is known as ‘petrichor’ and it is in fact a result of us smelling an organic molecule, geosmin, which is released as the Streptomyces dies or is consumed by other bacteria.
But how does a molecule in the ground get into the air for us to smell after the rain?
In short, it becomes aerosolised. As the raindrops hit the ground, tiny little air bubbles trap the geosmin, then shoot up through the raindrop and pop out the top releasing the aerosols into the air. A similar example is watching the bubbles pop off the top of a freshly poured soda or Coca-cola, where you are able to then smell the coke. The wind then carries the aerosols across the land.
It is difficult to comprehend the relief that the first rains of the season bring to such desiccated landscapes. After months of little to no rain, all organisms, big and small, come to life with the first downpour.
The word petrichor is derived from the Greek word, “Petros” meaning stone, and “ichor” meaning fluid that flows from the veins of the gods. An appropriate name and fairly apt description if you ask me. It was coined by two researchers in the 1960’s after they discovered that it was being captured as a fragrance and sold in Uttar Pradesh, India. The scent appeals to people because of its primal, primitive attributes and humans are particularly sensitive to it. In fact, human beings are more sensitive to the smell of geosmin than any other animal is, and this is a bold statement! Humans are more sensitive to the smell of geosmin than sharks are to the smell of blood. A shark can smell one part of blood per billion parts of water, whereas humans can smell geosmin at 5 parts per trillion. Sharks are designed to be able to smell blood to find food, humans must be designed to smell geosmin in order to find water.
The geosmin is released in aerosol forms that are ejected from the ground when raindrops make contact, these aerosols can be carried vast distances in the wind, hence why we can often smell the rain before feeling it.
The odour is especially evident after a prolonged period of dryness and it permeates the air in the early summer months of October and November. So the next time someone asks, “Don’t you just love that smell of the rain coming?” you’ll be able to tell them what it’s all about!
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Excellent blog, Robbie. “Petrichor” is a great word (as is the aroma), well worth knowing , but, alas, not many people here in the western United States seem to be familiar with it. So it’s sort of a “show off” word, too. I use it often, probably to show off.
Thank you, Dave. I’m glad you enjoyed the read!
Robert, well written explanation of the smell. I never forget the smell and now I know why, because humans always search for water. Thanks for teaching me something new.
You’re welcome, William. I’m glad you learnt something new!
Beautifully written, I love the smell of rain, especially when it’s hot!
Fantastic blog Robbie and thank you for the new word, petrichor, that I will use on my hikes after rain. There are so many wonderful smells whilst out in nature, not the least of which is new grass. Your blog brings up so many wonderful memories….
Thank you, Denise. I’m glad it created a bit of nostalgia!
Thank you, Francesca. Yes – don’t we all!
thank you, very interesting!
You’re welcome, Irene!
I know just what you mean, Robert – but let’s also not forget the wonderful aroma of a hot chocolate and Amarula on the morning game drive, and the gin in the evening…..
Both the aroma… And the taste!
Robert, this must be one of the most informative and interesting blogposts I have read here. Very well done, thank you.
You’re welcome, Dries. I’m glad you enjoyed it and learnt something new!
Yes, the smell of rain, or rather water hitting the earth, is wonderful, especially if it comes at the end of a hot day or even a very long hot and dusty period. It is so refreshening . A great article and wonderful photos.
Refreshing (and relieving) indeed!
Always love these postings of yours. So deliciously edifying!
That’s great to hear Johanna, I’m glad you enjoyed this one!
We have visited Londolozi usually in early to mid January and we don’t usually have downpours. And probably we don’t notice the effect of the rain on everything! Next time we come I will make an effort to pay more attention. Thank you. Victoria
That’s something to surely look forward to!
Fun and interesting read! Like the smell of cut grass, the smell of geosmin is capable of bringing back some happy childhood memories. Summer days of stifling heat and humidity were all movement felt impossible. And with that crack of a thunderstorm…running out to greet the rain! Thanks!
You’re welcome, Marcia. It too brings back happy childhood memories for me!
Robert your description of the smell of rain is incredible, the word Petrichor is not used often. I love the smell of rain and know it brings relief to all, animals, people and our bush.
Petrichor ! what an interesting word and what a super interesting blog Robert. It certainly brings back wonderful memories of growing up in the Lowveld..a smell that cleansed you from the inside out… but of course there was always that huge electrical storm first with massive lightning which would have us jumping out of the pool or bath as fast as we could go 😁.
I’m glad it brought back some happy memories for you Cally. Growing up in Johannesburg I too would be quick to get out the pool!
I had no idea that you can smell rain coming. How wonderful! Thanks Robert.
You’re welcome, Barbara. I’m glad you learnt something new!