The water cycle is the process that keeps our planet’s water in constant motion. From evaporation to groundwater flow, each step plays a vital role in shaping our environment and life on our planet. In this post, we’ll explore 10 key processes in the water cycle, breaking down how each one works.
Before we dive in: If you’re an educator planning to teach the water cycle, great learning resources are key to deepening understanding! I think you and your students will love my complete Water Cycle Unit (plus you’ll support my blog with your purchase! ❤️)
Evaporation
The sun is like the engine driving the water cycle. That’s because the sun provides energy for water to evaporate. Evaporation is the process of water changing from a liquid to a gas, called water vapor. Evaporation may happen anywhere that there is water; water evaporates from oceans, lakes, streams, soils, and even from raindrops as they fall.
You can observe and measure evaporation in your classroom. It’s an easy, hands-on science experiment. To try it, find the directions in my blog post about measuring evaporation.
Vapor Transportation
When you think of water moving, you may think of rivers and streams. But water also moves around in our atmosphere. Even though we cannot see it, air currents move huge amounts of water in the form of vapor across continents. This is why water that evaporates over an ocean can fall as rain over land.
Condensation
Condensation is the opposite of evaporation. It is the process of water vapor becoming liquid water. Condensation happens in our atmosphere all the time. It happens because as vapor rises in the atmosphere it cools, making it difficult to stay in the vapor form. This causes little liquid water droplets to form.
If you look up at the sky and see a cloud, you are seeing condensation in action! That’s right: when water condenses in our atmosphere, it creates clouds. Once the water condenses into droplets, they start to fall towards the earth. If the droplets make it all the way to the ground without re-evaporation, we get rain (or snow or hail if they freeze!).
You can learn more about condensation and the role it plays in forming deserts in my post about the rain shadow effect!
Precipitation
Precipitation happens when water falls to the Earth’s surface in liquid or solid form. This includes water in the form of snowflakes, hail, sleet, or liquid droplets (rain). Precipitation falls onto land or into bodies of water. A lot of precipitation falls directly into the oceans.
When precipitation falls on land, freshwater is formed! When water evaporates from the ocean, the salts are left behind. If the water falls on land, we get fresh water. That fresh water will start slowly making its way back to the ocean in streams and seeping groundwater or get stored in lakes and glacial ice.
You can make your own precipitation gauge and measure precipitation with a plastic bottle and a few other household items. Try it out in my blog post on how to measure precipitation with a DIY rain gauge!
Runoff
Runoff is when water flows downhill. This includes rivers, streams, and any water flowing over the Earth’s surface. Runoff happens thanks to gravity – surface water always flows from high to low elevation. You won’t see a stream flowing uphill. Little streams start high up in the mountains. They flow downhill and across the planes, joining together to make big rivers. Rivers make their way to the coasts, where the freshwater is returned to the ocean and mixed with salt water.
You can learn how to measure the water flowing through a stream in my blog post about stream measurements. It’s a simple activity that can be completed with a few household items and some math skills!
Ice Storage
Not all the water in the water cycle is on the move! Some water becomes trapped for long periods as snow and ice. In cold places like tall mountains and around the poles, frozen water doesn’t thaw, even in summer. In these places, water is stored as ice for centuries or longer! Examples include ice caps, ice sheets, valley glaciers, snowfields, and sea ice.
If you’re interested in learning more about snow and ice, read my blog posts about snow water equivalent and snow hydrology.
Infiltration
Infiltration is when water seeps from the land’s surface down into the soil. This happens when rain falls onto the soil and seeps in. Water also infiltrates downwards through the bottoms of some lakes and streams. Conversely, groundwater may also flow upwards sometimes – into gaining streams and springs.
If you’re interested in learning more about soil infiltration, try measuring it yourself! You can find directions in my blog post on measuring soil infiltration rates.
Plant Water Uptake
Did you know that plants play a role in the water cycle? All plants take up water from the soil through their roots. A single tree may seep up hundreds of gallons of water each year. Now imagine all the trees in a forest doing this – that’s a lot of water!
Transpiration
The water taken up by plant roots doesn’t just disappear. Some of the water is used in a chemical reaction called photosynthesis, in which it is combined with carbon dioxide gas to form oxygen and sugar.
The rest of the water evaporates out of the plant’s leaves in a process called transpiration. Plants have tiny pores in their leaves called stomata that open to release water vapor – similar to how you have pores on your skin that release sweat. The water vapor from the stomata is released into the atmosphere.
Groundwater Flow
Some of the water in the soil gets taken up by plant roots near the ground’s surface. But plenty of water continues to seep down into deeper sediments and rocks. The water fills the tiny gaps in the sediments and rocks known as pore spaces. Water in pore spaces is moving and flowing, just like water on the surface. But groundwater typically moves much, much more slowly than rivers and streams. Some groundwater eventually makes its way back to the surface, for example, into springs.
What’s Next?
Continue reading about human impacts on the water cycle. Or, find classroom activities for water cycle processes in my posts outlining classroom activities for evaporation, precipitation, infiltration, and stream flow!
I also created a few water cycle-related free printables and activities, which are available to my email subscribers on my free resources page. These free materials include my original hand-drawn water cycle diagram, water bingo, and printable directions for a freshwater visualization activity.
Teaching the Water Cycle
There’s no need to scramble to put together the perfect materials for a Water Cycle lesson – I’ve already created them for you! This set includes all the printable materials you need for studying the Water Cycle.
Explore more lessons from Wild Earth Lab:
If you enjoyed this post, I know you will love trying my other printable science and nature units in your classroom too!
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