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Last updated: 11th May 2023
The Water Cycle
Keywords
Water cycle, evaporation, condensation, precipitation, surface flow, subsurface flow, runoff, transpiration, clouds, atmosphere.
Introduction
The water cycle is the cycle of water from the ground, to the sky, to the ground again. It includes several steps, which we will have a look at now.
Starting Point - Evaporation
Evaporation is the process where water is turned into a gas and returns to the atmosphere. This is any surface water that is on the ground, lakes, rivers, ponds, even puddles. The water is evaporated by the sun, and goes up to the sky and eventually forms the clouds we see in the sky.
Interesting fact: once a tree transpires, the water from this process evaporates, so a tree also adds to evaporation.
Condensation
We all know condensation is where the water vapour returns to a liquid state and is usually found at the top of a kettle after it boils, or on your windows in the cold mornings. Even on your car windows in the same manner. But it also is the process when the evaporated water changes once it's at the upper atmosphere. It starts to condense back into water.
At some point at the higher point of the atmosphere, it will begin to cool the evaporated water, and it changes in matter to a what we term as a cloud. These clouds form, first a little wisp, and then as it progresses, it gets bigger and bigger until it eventually rains. These clouds don't always necessarily drop the rain straight away, as they can be moved along by the wind.
Precipitation
Precipitation is commonly known as rainfall. This is what happens with the cloud once it has reached an optimal point of saturation and weight. Yes, weight really does have a lot to do with it. If the cloud is not heavy enough, it will not fall as rain. Also, to make it worse, the right conditions are not met in the fact that it needs to be a few degrees cooler for it to rain, at least in the atmosphere just below the cloudline.
The clouds will change colour when it is due to start raining. We usually depict clouds as being big, white and fluffy, but when it rains, they become angry, grey clouds.
Surface and Subsurface Flow
When it rains, there will be surface flow. This is the excess rainfall not seeping into the ground (it could be very dry, or the water table has been met) and flowing off the ground. If you think about it being on the road system, it would be if the drains were blocked, and the water has nowhere to go, it will simply run to the edge of the road, and flow along it (assuming there is a path and kerbside there).
Subsurface flow is the flow of water underground. Even though rainfall may attribute to this a little, it is mostly the movement of water from natural springs, or rivers that run underground.
Runoff
When it rains, snows or hails, where does the resulting water go? With snow, that's fairly easy to explain if it remains there as snow, as it's right in front of you, but what about the excess water? This moves around the Earth in an effect called runoff. The water will run to somewhere. Anywhere. If it can go in a hole, it'll fill it. If in the open, it will runoff into other bodies of water - rivers, lakes, streams.
Transpiration
Transpiration is the movement of water through plants. The water travels up through the roots, throught the plant stem and leaves (which uses some of the water in process), and then out through the top of the leaves or branches. This is then attributed to evaporation.
You have now come full circle. These are the basics of the water cycle.
Here's a YouTube video from BBC Teach to explain more:
Too Long; Didn't Read
Water is on a continuous cycle around the Earth. From a starting point of evaporationWhere water is turned into a gas and returns to the atmosphere above., through condensationWater in a gas state returns to a liquid., precipitationRainfall from the sky. and surface and sub-surface flowAbove ground and below ground movement of water., the water cycle goes through a series of stages, before returning to the original stage where it began.
The water cycle is never ending, and complements our planet with a seemingly endless supply of fresh water, which can be filtered and obtained through large vessels - to be used for watering garden plants, filtered or heated to drink, or used elsewhere. It helps plants grow in places, provides underground reservoirs of water in a phenomenon called the water table, and provides areas with fresh springs that come up from under the surface for us to use.
Footnotes
[1]A simple, funny representation of part of the water cycle, image courtesy James of No Trades.
Carbon Cycle
Weathering & Erosion
