What is the water cycle?

Our planet is known as the blue planet, over 70% of it is covered in water, most of which is the Ocean.

This water shapes our landscapes, influences where life thrives, affects the health of our Ocean and the weather in our skies. 

The Ocean is always closer than you may think (not in a sinister, about-to-jump-out-at-you way. It’s more of a realising-it-is-Thursday-and-the-weekend-is-only-round-the-corner-kind-of-way). 

Take a moment, think: what is different from the water you drank this morning (if you haven’t had any, this is your reminder to drink some) and the water lapping up a warm tropical beach? Every drop of water, from what’s come out of your tap to the water five kilometres deep in the middle of the Pacific, is connected.   

It is all just at different points in the water cycle. 

How does the water cycle work? 

There are four processes that drive the water cycle: evaporation, transpiration, condensation and precipitation.  

Water is warmed and evaporates, becoming water vapour. Amongst the many good things plants do, they release water into the atmosphere through transpiration. These two processes are responsible for putting water vapour in our air, our atmosphere.  

Water vapour is invisible.  

The steam we see when we boil the kettle (or the clouds in the sky) is water becoming liquid again, on contact with the cooler air. That is condensation, the transition back from gas to liquid. When enough of this cloud cools and turns to water, it will clump together and fall as precipitation (snow, hail and rain).  

How is the Ocean connected to the water cycle? 

This water then starts its journey back to the centrepiece of the cycle: the Ocean. 

The Ocean holds 97% of the Earth’s water – approximately 1.34 billion cubic kilometres. 86% of evaporation is from the Ocean, and 78% of precipitation re-enters the Ocean, directly. You can’t have the water cycle without the Ocean. 

Ice holds 2% of global water and just 0.001% is in the atmosphere – that is all the clouds in the sky.  

But if we add all that up, there’s a little still on the table – or more accurately, on land. That is the groundwater, lakes, swamps and the rivers. Rivers make up only 0.0002% of the total water on Earth.

What does the water cycle do? Why is it important? 

There are five main points of importance for the water cycle: 

1. Regulating Climate:  
The water cycle helps distribute heat around the globe, influencing weather patterns and climate conditions. It absorbs and releases energy during evaporation and condensation, which affects temperature and weather. 

2. Sustaining Ecosystems:
The water cycle provides the water necessary for plant growth and supports all forms of life by delivering freshwater to ecosystems through precipitation.

3. Shaping Landscapes:  
The water cycle contributes to erosion and sedimentation, reshaping geological features over time. 

4. Circulating Minerals and Nutrients:
Water transports minerals across the globe, enriching sea and soil and supporting plant life. 

5. Maintaining Freshwater Supplies:
The cycle replenishes freshwater sources, such as rivers and lakes, which are essential for human consumption and agriculture. 

Imagine a world without a water cycle – what would it look like?  

How is the water cycle changing?  

Human activity is interfering with the hydraulic cycle at every stage.  

Deforestation means less trees to transpire and absorb rainfall. Urbanisation interrupts drainage and can increase surface runoff. When it rains, the water that would have been absorbed by the ground now hits tarmac and runs down the road. 

The single greatest threat to the water cycle, and therefore to all life on Earth, is climate change.  

How is climate change impacting the water cycle?  

Climate change is intensifying the hydraulic cycle. Higher temperatures lead to more evaporation, more water vapour in the atmosphere, which results in more intense storms and rainfall. At the same time, droughts are becoming harder to predict and more severe.

These changes directly threaten our lives. 

Water is the life blood of our planet, and the water cycle is the pulse that keeps it alive. 

The hydraulic cycle regulates our climate, fertilises and maintains our ecosystems and shapes our world. We are changing it through our actions and activities.  

Understanding this cycle is the first step, but acting to protect it is the most important. The question is: what will we do to safeguard the blue heart of our planet? 

Post by

Will Steen