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Good day STEM. In my last article, we took a dive into the world of water and its importance to life. I wrote about the science behind the structure of the water molecule, And we got to understand that most of the properties and qualities of water (such as its solubility, surface tension, and enormous specific heat) are a direct consequence of its polar structure. We also got to learn about the uneven distribution of water on our planet and we learnt that these regions simply act as water storage systems for the planet. Just to bring my readers up to speed, you should know that there's water on the ground as surface water, under the ground as groundwater, there's water in the atmosphere as vapour, and there are ice sheets and glaciers as well. These are the storage systems.

I also did mention that water existed in the biosphere too. However, I didn't state just how much water existed in the tissues of plants and animals combined, and that is because the amount in percentage is negligible on the grand scale of things.

Today, we'll be discussing the mechanism behind the existence of water in these 'storage systems', and how they move from region to region over time. We will be talking about the hydrological cycle, or the water cycle.


<div class="pull-right">https://c1.staticflickr.com/9/8448/7920558736_811238642c_b.jpg<center><sub>  [CCO licensed,]: <a href="https://www.flickr.com/photos/shankarvinod/7920558736" rel="noopener" title="This link will take you away from steemit.com">Flickr </a></sub></center></div>


The water cycle is important to life on Earth and goes a long way to shaping the way our world looks. Apparently, the amount of moisture in circulation is finite and remains fairly constant through time and age. That is to say that there's pretty much the same water on earth as there was a million years ago. Even though some lakes and lodged water have dried up, the water did not just disappear into the ether. It is, however, a part of the hydrologic cycle and is transported from one form to another. Hence, the water you have in your teacup might have exactly the same water molecule a dinosaur drank about 50 million years ago.

Going by [the Webster's dictionary](https://www.merriam-webster.com/dictionary/hydrologic%20cycle) definition; The water cycle is the sequence of conditions through which water passes from vapour in the atmosphere through precipitation upon land or water surfaces and ultimately back into the atmosphere as a result of evaporation or transpiration. 

Sounds clear enough? without the prior knowledge of the terms, I doubt it would. Simply put, it is the continuous movement of water on, above, and below the surface of the earth. <sup>[source: [wiki](https://en.wikipedia.org/wiki/water_cycle)]</sup>

Not all of earth's water is involved in the hydrologic cycle at the same time though. Else, we wouldn't have oceans. The ocean takes up over 97% of Earth's water and is its biggest 'storage' amongst all the four spheres. Groundwater and glaciers share a 2%, and the rest occur in the atmosphere and in biology. The hydrologic cycle features the interrelationship and connectedness between these storages. Moisture is ceaselessly being interchanged regardless of its physical state or location on geography, and the amount of water in each storage reservoir remains fairly the same because the cycle goes on continually. Hence, we have the ocean's water remain almost the same even though a large amount of evaporation goes on even in cold temperatures.
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# <center>The processes</center>
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<center>https://c1.staticflickr.com/9/8083/8265046380_4bfb79a5c4_b.jpg</center> <center><sub>[The water cycle: [Image: CCO licensed, AIRS, Flickr](https://www.flickr.com/photos/atmospheric-infrared-sounder/8265046380)]</sub></center>

The processes behind the water cycle are simple to comprehend, and owes a lot to the presence of heat from the sunlight heating the earth. In summary, moisture evaporates from the earth's surface as vapour into the atmosphere, where it undergoes condensation and precipitation to fall back to the earth's surface as water or ice (depending on the season of the year), and then run or trickle into these storage areas to begin the process all over again by evaporation. As long as it isn't absolute zero, there's just enough heat for evaporation to occur. The major processes in the water cycle include:
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* Evaporation, sublimation -as in ice-, or Transpiration -as in plants-. ---  (Surface to air).
* Precipitation --- (Air to surface).
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Any other Process in-between or after precipitation to continue the process are minor, and that's because they are rather seen as the transportation of the moisture from a particular region to another through winds, air movements or as runoffs on the mountain tops. They may include:
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* Advection (which simply is the horizontal movement of the water molecules in the sky)
* Condensation to form clouds which bring about the precipitation, or ice crystals to form snow.
* Surface runoffs from hill-tops or as subsurface flow through underground paths to major water lodges.
* Deposition as water molecules in air freeze into ice directly without being liquid.  
* Refreezing of the water molecules as ice in glaciers and high latitudes areas where the temperature is low. 
* Melting of the snow crystals into liquid water to evaporate into the atmosphere again. 
#
We shall discuss these points under the major processes - Surface to air, and Air to surface!
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# <center>From Surface to air. -- Up, Up and Away!</center>

<div class="pull-right">https://c1.staticflickr.com/9/8453/8058464813_ffae1c7c5c_b.jpg<center><sub>  [Transpiration in plants. CCO lincensed]: <a href="https://www.flickr.com/photos/sgendera/8058464813" rel="noopener" title="This link will take you away from steemit.com">S. gendera, Flickr</a></sub></center></div>

As mentioned earlier, moisture evaporates from the earth's surface as vapour into the atmosphere. About 85% of the water in circulation comes from the ocean, establishing it as one major contributor to this cycle. It is estimated that an annual volume of about 434,000 km<sup>3</sup> of water is evaporated from the oceans' surfaces. However, it is not the only source. the phrase 'Earth's surface' could imply a lot of things, and evaporation can take place from just about any surface nonetheless, as long as such a surface is not without moisture.

In a way, the surface-to-air mechanism is all connected. Moisture from ice caps and glaciers constantly sublimate at cold temperatures into the atmosphere, groundwater rush through steep paths to join the oceans at some point, and lush green vegetation that are exposed to sunlight lose just as much water to the atmosphere as the ice caps after they have taken water from the moisture in the soil through the roots.

As the water vapour gets into the atmosphere, the cycle doesn't just flip the other side and drops everything back down as precipitation at once. Rather, it takes time, and the vapour would remain in the atmosphere for a short time. This could take hours, days or weeks, depending on the geographical area. During this period, the water molecules may be transported from one place to another through air movement (Perhaps higher up the atmosphere by convective wind currents or to other regions entirely by advection).
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# <center>From Air to Surface. -- Making it rain!</center>
<center>https://images.pexels.com/photos/52851/pexels-photo-52851.jpeg?auto=compress&cs=tinysrgb&h=650&w=940</center> <center><sub>[CCO licensed: [Pexels](https://www.pexels.com/photo/plant-leaves-green-close-up-52851/)]</sub></center>

Sooner after the water vapour gets into the atmosphere, condensation takes over and the water vapour is turned into liquid water molecules again or sublimated into ice crystals to form the clouds. Hence, some of the clouds we may see floating past are simply light-weighted ice crystals carried about by the wind high up in the sky. With time, these crystals collide and coalesce with each other to form water droplets and then build up over time to become heavy enough to fall back to the earth's surface as precipitation. Precipitation isn't a simple process because it is not every cloud that eventually precipitates. Water droplets itself are very light and are buoyant in the atmosphere, so it would take days for them to reach the ground, and a larger part of them would simply evaporate while descending through hotter air regions in the atmosphere. Hence, it would require billions upon billions of water droplets to form a cloud that is heavy enough to form raindrops which could then fall under the influence of gravity.

That said, it is important to note that these precipitations do not always have to be rain. Precipitation includes other forms such as hail, snow or sleet. Also, since the whole thing is in a continuous cycle, the rate of evaporation to precipitation would always balance out in the long run, except for the fact that they won't balance out in the same places or regions. This is because the evaporation from the ocean is higher than evaporation from continents and lands, and there's always a very high possibility that as the water vapour ascend, they are carried away by the wind to other regions, hence they don't always fall back into the same ocean they came from. thus, precipitation is higher on lands than evaporation. This balances out pretty nicely and helps transfer water to inland vegetations that are very far away from ocean bodies. Thanks to advection.

As precipitation occurs on the surface of the ocean, it is simply added to the teeming gazillion water molecules of the sea. When they fall on land, however, they fall on the leaves and branches of plants in vegetative regions first. After a while, the foliage gives way and the rest of the precipitate trickles or drips down to reach the ground.

On non-vegetative and bare lands, the water molecules simply seep into the soil at once, and would collect right there on the surface to form stagnated water if the amount of precipitation is pretty high. Others would runoff slopes to find a common point to lodge at the base to form a pond.

It should be noted that evaporation happens at every point. Hence, some water molecules will evaporate into the atmosphere as they land on warm surfaces, on the branches and leaves of trees and plants, and on the soil. However, this is quite negligible.
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## Conclusion and my thoughts. 

So there you have it about the hydrological cycle. It goes without saying that this cycle is very important to life since it is always refreshing for precipitation to occur in areas where there's hardly enough water for storage. This is not just for the people living in such areas alone, but for plants without deep roots too because, over time, the moisture content closer to the surface in soils tend to reduce or continually sink down to aquafiers, Thus, making it harder for these plants to get enough water from the soil. If the plants die off because of the lack of water, we could see desertification of more lands and the primary feeders (herbivores) would be affected too. And so would the secondary feeders, and within a short time, It would upset the flow of life and things could go wrong pretty fast.


<div class="pull-right">https://c1.staticflickr.com/5/4279/35069943644_fff6fb8fb4_b.jpg<center><sub>  [Lightning (electricity) on water brings about electrolysis, which decomposes water into its component elements - Hydrogen and Oxygen.]: <a href="https://www.flickr.com/photos/fireatwillrva/35069943644" rel="noopener" title="This link will take you away from steemit.com">CCO licensed, Flickr. </a></sub></center></div>

Also, even though a larger amount of the water molecules from precipitation is from the ocean, precipitated water isn't salty at all, and since water on earth's surface starts dissolving almost anything with time, precipitated is the purest form of natural water. Oh, and did I mention that **plasma activated water** (call it electrocuted water if you like) has a greater yield effect on crops than normal water? Well, during a lightning storm, some precipitation might have been struck by lightening enough to ... In an experiment carried out by Analytical Chemist and [TEDx Arnhem speaker](https://start-life.nl/archief/thunderstorm-technique-sustainable-crop-growth-founder-story-vitalfluid/) Paul Leenders, Plasma activated water has proved to be as good as any disinfectant or hand wash we have on the shelves in our local stores. In the future, man could apply this to agriculture and we could see a lesser use of expensive fertilisers which by the way contain some harmful chemicals which were mixed in there with the intent to kill pests. We could get the chemicals out of our food chain for good.

Learning, researching and writing Science over the past few months have taught me that life on earth is interconnected with probably everything we could think of. From their microstates to their mega macrostates, there is always a connection if we observe things closely. The hydrologic cycle is one of those processes that nature has got going for us that we should be thankful for.

So the next time it's Thanksgiving, add this to your gratitude list! 

## <center>Thank you for reading</center>
##### <center><sup>This article was done at a mentor's behest! :p</sup></center>

<sub>PS: Think you've got what it takes to write STEM-related articles? Find us on our discord server by following [this link right here.](https://discord.gg/PHkdQR) We have materials and an excellent team of mentors to help you get up to speed.</sub>

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