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PORTLAND, Ore. (KOIN) – Have you ever wondered, where does rain come from, or why does it rain so much here? This lesson will discuss that idea!

This is what we call the water cycle or hydrologic cycle. The water cycle is exactly what the name suggests: it’s the circulation of water in the atmosphere. This is such a fascinating concept and an important part of our earth since it shows how water is transported from one location to the next in multiple forms.

Weekend Meteorologist Joseph Dames

Some of the concepts we will briefly touch on in this lesson are: evaporation, condensation, precipitation, transpiration and runoff.

The best way to visualize what is going on around you, is to watch the video or check out the graphic of the water cycle provided before we continue. Then try to imagine it when you’re outside playing or visiting the beach with your family in the future.

What is unique about the Pacific Northwest is that we have the ocean nearby and a set of mountains to help envision how it is working on a local scale.

Now since the ocean occupies over 70 percent of the earth’s surface, and of course the Pacific Ocean is Oregon’s neighbor, we can think about the start of the water cycle there.

When the sun shines down on the ocean that energy will transform liquid water into the gaseous state of water vapor. That is the process of evaporation, which you can see in the water cycle image. Try to follow along with the image as we walk through the water cycle!

At that time the water vapor changes back into liquid, forming clouds! This is the process of condensation, which you can see with the clouds above. Guess what happens next? The wind will then transport the moisture to other regions where the process of condensation takes place. It is essentially an ocean above our heads!

Clouds roll in over Vancouver, Washington. September 28, 2019 (Courtesy Pam Zelinsky Copas)

Now once the liquid grows (and solids), it may start falling to the surface. This is what we call precipitation. Of course, that is usually rain, but it may also be snow or hail. Precipitation by definition is considered any form of water that falls from a cloud and reaches the ground.


This is when the cycle starts to return to the original origin of the ocean. If the precipitation from the clouds falls over the ocean or another water source, it will then return to the water cycle. However, we know that it doesn’t just rain over water and most of the time it is over land (when it impacts humans). Then the water must take a scenic route or longer journey back to a water source. How does it do that?

Plants collecting rain

One particular way is from plants and vegetation. When it rains the plants will catch that water and eventually give it back off to the atmosphere in a process called transpiration.

Finally, water will find it’s way back slowly to a stream or the ocean through the process of runoff. When it rains it will travel like a temporary stream downhill to a river or a larger water source. It may also travel through the ground around the soil and rock where it eventually will find it’s way to the groundwater if not a stream.