The Water Cycle

Actually, this is the part of my series that I am most excited to write about. Water is my ‘specialty’, my expertise. Throughout my studies I have always focused on water in a chemical, an engineering, an ecological, a climatic and a political way. Water is my passion. Sounds a bit weird right? But for me, water is the soul of our planet. Water is art, water is life, water is everything. Sounds a bit spiritual but, seriously, it is!

Last week we talked about climate vs. weather and what influences climate. Mainly we talked about global wind patterns that connect us all. They will also play a part in the water cycle as precipitation (rain, snow, hail, everything that comes down from the sky basically) is formed along those wind patterns.

Alright, let’s dive in to it, we’ll make a journey around the globe today.

A simplified version of the hydrological cycle. Water goes back into the atmosphere by transpiration from plants and evaporation from open water. There it condensates and comes back down as precpitation. Arrows point the direction from lake and trees up to the sky into clouds and back down on mountains and land.
The hydrological cycle – a raindrop comes down to Earth and takes different paths until it ends up in the ocean and eventually, back in the atmosphere where it comes back down as precipitation.

Let’s start at the top: One rain drop falls out of a cloud above land and lands on a forest. Here it can take several paths: It may infiltrate into the soil and become groundwater. As groundwater it might end up in a river that flows into a lake and further, into the ocean. Or, the drop infiltrates into the soil where plants take it up through their roots and transpire it back into the atmosphere. Or, the third option, it might just land on a leave in the forest and directly evaporates back into the atmosphere from there, forming new clouds and precipitation to close the cycle. It may also land on a mountain and be stored in a glacier for thousands of years.

Poor little drop getting all dirty

It can also fall on cities and towns where it is usually impossible to infiltrate into the soil because of all the concrete. So the little drop may end up in the sewer system getting all dirty and contaminated. Also the sewers have an end and so the little drop could make it all the way to the next big river that brings it to the ocean. In this case the little drop arrives with the leftovers of our medicine, some micro-plastics and other toxic particles. Ugh!

It’s not the drops fault but it will spread the contamination on its way. It may travel a bit further in the ocean and then evaporate where it will form a new, contaminated raindrop that may fall to the Earth at a place that has nothing to do with these harmful substances. Or, the other option is, it will sink down to the bottom of the ocean where it takes about 10.000 years for it to come back up to the ocean surface. This is fancily called the thermohaline circulation or ocean conveyor belt which you can see in the video below.


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You see, that’s how micro-plastics end up at the bottom of the sea. That’s how our bad choices, our dirt spreads around the globe. Every river leads to the ocean at some point, no matter where you live, you are connected to it. You throw your cigarette butt on the street, it ends up contaminating 1 m³ of water. That is 1000 l of water (264,17 gallons for the Americans here). 1 cigarette butt = 1000 l of polluted groundwater. Think about this next time. The same accounts for spitting your chewing gum out in a park or on the street. You are making your own precious water undrinkable. For what? Not having to walk a couple meters to the next garbage bin?

Remember the little rain drop. That little guy takes it with him, everywhere he goes. And he goes everywhere!

One way or the other, the little drop will rise up, back into the atmosphere. It may only take a couple of days or 100.000 years, the cycle will close eventually though. Now, let’s talk about rain…

How does rain form?

First, liquid water changes into another state, of course. Water becomes water vapor, one of the most abundant natural greenhouse gases. Usually a raindrop forms around a tiny little particle because energy-wise it’s easier to form around something that already exists.

Naturally, water condenses around dust particles that come from deserts for example. Or ashes from volcanoes that we can’t see. Again, humans changed this a bit and rain also condenses around aerosols, things that we emit through industrial processes or riding cars for example. The raindrop also takes these aerosols with it, down to the Earth’s surface, spreading toxic aerosols where ever it may end up.

Now what I love most about water is that we can seriously follow this journey by looking at its chemical compounds.

What makes water a climate archive?

As water is trapped in the Arctic as ice, for example, it captures the signature of the atmosphere of the time it last saw the surface. This means that snow that fell in the Arctic 150 or 1500 years ago was buried underneath other layers of snow. As the snow layers got heavier and heavier, the initial layer was compacted and buried with it the some air bubbles that let us draw conclusions about how warm or cold the Earth was at the time it snowed.These air bubbles also contain CO2 and Methane for example, which is why we know for sure that there is more of those greenhouse gasses in the atmosphere now then there ever was before in the time of humans.

You can imagine this a bit like counting tree rings. It’s pretty accurate, we know that a wider tree ring means warm, wet conditions while thin rings mean dry, cold growing periods for the trees.

It gets even better!

We can even apply this to your teeth and your hair! If you grew up let’s say in the mountains, your tooth enamel shows that. That’s because water consists of H and O, hydrogen and oxygen. And there are heavier types of oxygen and lighter types of oxygen. Most of the heavy oxygen doesn’t make it all the way up to the mountains and the rain on higher altitudes consists of more light little oxygen atoms. The heavy ones usually rain down closer to the shore or closer to the source where the rain initially formed.

Agua Azul Waterfalls in Palenque, Mexico. Shown during rain season where the water is of a darker color. The waterfalls are framed by lush rainforest and steam is rising from the water.
The power of water beautifully shown by the Agua Azul waterfalls near Palenque, Mexico.

And your tooth enamel takes up those atoms when it first forms. So one could see that you must have lived in higher altitudes during that periods because the oxygen atoms in your enamel are lighter than those of people who grow up at a beach for example.

This also means if you first grew up in the mountains and the moved to a beach town, we could see this in your hair. Your hair holds the information of where you drank water in the past 3 months of your life. That’s also how criminal cases are solved sometimes.

Back to the initial question

I digressed a bit but I found this so exciting when I first heard about it. And it just shows that our water imprints on us and our surroundings. This makes water or better, deposited water in any form, an archive. We our selves are a climate archive with our teeth and hair. But so are glaciers, corals, stalactites and stalagmites, bogs and basically anywhere where water accumulates.

By affecting the cycle, e.g. by building concrete cities and roads and emitting toxic substances into the air that accumulate, we also have an impact on our water. As water forms around those substances as rain and carries it into the groundwater, glaciers and the oceans, we make our own water unusable in the long-term.

It’s not really a visible connection, I get it, but the cycle goes on and on, water spreads around the globe, the deep oceans and high mountains. 70% of our planet is covered in water. Only 2,5% of those 70% are freshwater. And of those 2,5% freshwater, 1,75-2% is frozen in glaciers and only 0,5-0,75% is actually groundwater that we can access. Only 0,01% is surface water such as lakes or rivers.

So, you can see how precious water is

If you live somewhere, where drinkable water just comes out of your tap, you are extremely lucky! And with climate change, there is the serious question of how much longer you/I will be so lucky.

Also I hope to have shown you how water, like wind, connects us all, whether we are aware of it or not. We are not alone on this planet and our (dirty) actions have an effect on other people’s lives, often a more severe effect than they have on our own life initially.

Tell me, how is water treated where you live? Is it scarce, is it abundant? Is it a commodity or ‘just there for all’ or something sacred? Are you doing anything to preserve water? I am curious to hear from you guys!

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