Earth’s Water Cycle: A Guided Discovery
I watched, from the comfort of my Arizona home, as snow piled up on the East Coast this last month. Record levels in some areas. Once that melts that’s a lot of water. (Discussions of Flint Michigan’s water problems also has me thinking about water as you probably are too).
Preschool and early elementary school science curriculums often include a unit on the water cycle. With any snowstorm or rain shower, you can boost understanding of where water comes from and where it goes. You and your child may have already had relevant conversations. Here are some ideas on how to sustain that interest and keep building knowledge.
These days some of you are living in areas of drought, thus, your child may have some awareness of and be curious about water shortages. Others live in areas where rising sea levels or swollen rivers present flooding threats. Again, your child is probably aware of those possibilities from overhearing conversations among adults. Even if you do not live in areas where water, too much or too little is an issue, which given recent national weather events would be surprising, understanding the water cycle is a basic concept in earth science and worth delving into.
If you see an opening, initiate discussions about this topic. Talking about the water cycle, droughts, or flooding can’t undo some of the concern your child may be experiencing about these weather events, but having information and a willingness to explore is a whole lot better than doing nothing.
Every time there is wet weather or precipitation, or when you drive by a waterway (including over the dry river beds here in the Southwest), you have another opportunity to reinforce the lessons associated with the water cycle. In exploring these issues you and your child can consider science fair projects every day!
There are already a number of informative resources on the water cycle that should help you help your child find answers. In case you, as a guide, need a reminder of what the water cycle is here is a great video explanation.
Here’s another video that may help to get your child interested, but remember you still need to reinforce learning with repeated discussions, observations, and hands-on experimentation.
One other precaution is that it is easy to think that the rain coming down on my head came from the puddle I observed the week earlier that subsequently evaporated. But no, this is not the case. Water does not fall exactly where it evaporated. That is, water does not just go straight up and straight down. That raindrop on your nose could have last been in a river in China, evaporated into the atmosphere where it travelled until it condensed out over your present location. Water is constantly in motion with the sun’s energy and gravity keeping it in circulation.
Furthermore, consider this amazing fact. The water on the earth and in our atmosphere today is thought to be the same water that was here billions of years ago!
Where does rain/snow/sleet/hail come from?
How did the water get into the clouds?
Where does it go after it hits the ground?
What is evaporation?
What is condensation?
What is a cycle? There are a lot of natural cycles. For example, a common one would be the annual cycle of seasons. (You can ask whether your child can think of other words that include “cycle”, such as bicycle and tricycle).
Like those wheels on a bicycle, water goes around and around in a cycle, as the following observations, measurements and these informal lessons will demonstrate.
On a rainy day, have your child step outside and take a look at what rain is and where the rain comes from. The answer may seem obvious, or rain is water and it comes from the clouds above. Take a look on a windy day, when the rain may look like it is coming sideways. In other words, don’t take for granted that your child knows what rain is or where it comes, but look, ask and listen. (While observing you can also try and help your child find language for what the rain feels like, tastes like, smells like, and sounds like). Drawing is great as it forces one to consider the details.
What is rain? (water droplets) Where does it come from? (clouds) How can you tell it comes from clouds? (There can be clouds in the sky and it doesn’t rain, so just saying rain comes from clouds is not sufficient. Perhaps it is time to talk about the types of clouds. See our post on weather: http://guidingcuriosity.com/weather-wow/ )
Repeat these observations on days with different, but wet weather or other precipitation events. Take a look. What do sleet, hail, or snow look like or what are they made of? (Sleet and hail originated as water droplets as well. Snowflakes or snow crystals are from water vapor.) For more information on snow crystals see a recent post http://guidingcuriosity.com/frozen-water-vapor-snow-crystals/). Where does snow, sleet or hail come from? (Clouds). When you are standing in a fog on a foggy day, you are literally standing in a cloud that just happens to be at ground level.
Is there a pattern emerging…water from clouds?
Don’t forget about the role of gravity in this process!
Water Cycle Step 1: Water in the atmosphere reaches earth by precipitating.
Once rain, sleet, hail, or snow hit the ground, what happens or where does it go? Snow just sits there for a while so may be less interesting initially, but as it begins to melt, make an observation on where the melting run off goes. It should be easier to track rain. Look for flowing water as well as standing water or puddles. What is happening or what is going on?
For many of you living in urban and suburban areas, the answer to this question is that the melting snow, rain, sleet or hail flows down sidewalks and streets and into the drainage grates. This is the beginning in observing or thinking about where the water goes. But once it flows through the grate, where does it go next? You may not be able to make an actual observation to answer this question. But ask and see what your child is thinking about. Introduce the notion of all of the infrastructure underground, engineered to take the water away and into underground storage or emptied back out into a river (after treatment). Great engineering lessons here!
Here is a good explanation based on what happens in the Cleveland Ohio area, but I think you could talk it through based on where you live.
If you live near an urban stream, perhaps you can find water running into the stream.
For children in more rural areas, they are more likely to experience the drainage of water into gullies, streams, and rivers.
Does all of the water flow off the surface? Flowing water is more interesting to watch than water seeping into the ground, but this is what happens to most of the water. The water that flows cannot be absorbed because of the concrete/asphalt, the type of soil or the fact that the ground is already completely saturated. While not as exciting, you can still talk about what it looks like or what is happening if the water gets absorbed?
The main point is that the water flows or is absorbed. It needs somewhere to go when it accumulates. This is the observation you are hoping your child will arrive at and find the language to express that understanding.
The next telling observation may depend on where you live. Do you live where your child can experience a stream flowing into a river, or a river into a lake or even the ocean? In an urban setting, you may be able to make observations at drainage ditches or canals. If you can visit an area where there is a confluence of water ways, see if your child can generate the language for what is going on.
If visiting such an area first hand is not an option, maybe look at an atlas, find a stream or river and follow its course into another river, or perhaps a lake or the ocean. Here are aerial photographs that show this clearly. Examine them together asking your child what is going on?
Water Cycle Step 2: Water flows, becoming part of a lake or seeps into the soil.
So water comes from the sky and the makes its way from a stream or river into a lake or the ocean. Some of this flow can actually be underground as groundwater and invisible to the eye. Then what happens to it? Answering this last question will depend on your child’s observations or evaporation and condensation during the experiments below.
Water Cycle Step 3: The sun’s heat causes liquid water to evaporate and turns it into water vapor. This process is better experienced first with hands-on activities prior to an explanation.
Water Cycle Step 4: Warm air containing water vapor rises. When in the atmosphere it meets cooler temperatures and that water vapor condenses becoming clouds. When the water particles that are the product of condensation become large enough, gravity pulls them down. Depending on the temperature, those droplets could be rain, sleet or hail, or if the vapor freezes directly the result is snow crystals.
Compare and Contrast
What is a lake compared to an ocean? (Size is the biggest difference. Oceans are huge, although lakes are large bodies of water. Oceans are salt water while most lakes are fresh water. Oceans have boundaries, but those boundaries are harder to determine. Lakes are surrounded by land. Also, most of the time water can flow into and out of a lake, but it only flows into an ocean. When water can only flow into a lake, the lake can become very salty over time. Think of the Great Salt Lake in Utah).
What is a pond when compared to a lake? (This is kind of a trick question as apparently there is no universally accepted definition of a lake or pond that would draw a clear distinction. In general, lakes are bigger and deeper. Because they are deeper, there is normally no plant life on the bottom because of lake of sunlight.)
What is the difference between fresh and salt water? (Another trick question. It seems obvious, right? Salt water has salt in it. But fresh water can also have some salt in it. So the difference is the amount of salinity or salt water has a greater concentration of salt. About 97% of the earth’s water supply is salty. True fresh water bodies are rare on earth. About two-thirds of the fresh water supply is locked up in glaciers and the polar ice caps. Now may be a good time to remind a child not to drink salt water).
What is the difference between evaporation and condensation? (These are daily phenomenon worth understanding. In the simplest terms possible, both represent phase changes in matter. Evaporation is changing a liquid to a gas. Condensation is the reverse or changing a gas (or vapor) to a liquid. There are actually two types of ways to change a liquid to a gas, or two types of vaporization: evaporation and boiling. Evaporation occurs on the surface of the liquid and depends on sunlight, wind, or temperature. Condensation also depends on a temperature but a colder versus warmer temperature.
Collect rainwater near your house. If you know it’s going to rain, put out a pan (pie pan?) and measure the height of the water in the pan after the rain stops. How much rain as measured in height fell during that precipitation event (or rain shower)? You can pour the rain into a measuring cup and determine the volume of the rain you collected, but the common measure of the amount of rain is height.
Try this again, or put the pan out and observe daily. Following another rainy day measure how much rain fell. After the measurement remember to empty the pan. Keep track of amounts of rain over a period of a week or, if your child is patient, a month.
Compare the average rainfall in your area with rainfall where a friend, cousin, or grandparent lives. Who experiences more or less rain? How about looking up the average rainfall in your area and comparing it to where there is the least or most rain in the world. Annual total rainfall can vary from 0.1” to 900 inches. How close are you to the least amount or to the most?
If you collected water in a pie pan and measured it. Make note of the time that the rain ended. Keep an eye on that pie plate. How long until the water disappears or evaporates?
Collect snow in a bowl or other container. Fill a bowl or container with water then pour that water into a measuring cup so you know the volume of water the container holds (or use a large measuring cup). Next, collect snow in that bowl or container. Pack it down and level off the top the way you would level baking flour if using it in a recipe. Bring the snow inside. When the snow melts, measure the amount of water left over. How much is there? Is it more or less than the amount of snow based on the size the container would hold? What happened? (Snow crystals are filled with air. When the snow melts, the air is released so the remaining water takes up less space.)
Here are some interesting numbers to consider. Is your child ready for percentages? Is there a way you can depict this to show what the difference between these two numbers is? In the US, 70% of the annual precipitation returns to the atmosphere via direct evaporation (see experiment section below if you have not already explored the meaning of this term). The remaining 30% reenters through run off, or flowing into streams and rivers or moving more slowly through the ground (aquifers). Eventually, this water too will be evaporated, but the route is slower and less direct.
Lets start with this reminder. Water can occur in three physical states: solid (ice), liquid, and a gas. Transitions between states of matter are known as phase changes. Is your child aware of these common every day changes such as evaporation (liquid to vapor), condensation (vapor to liquid), freezing (liquid to solid), melting (solid to liquid) or even sublimation (solid to vapor)? That is, water can appear in different forms. Ask her to point out examples of these different states that water is in. If you are cooking a meal, you will have several opportunities to point this out.
Ask your child to help hang some wet laundry outside. Or just wet a wash cloth and hang it in the sun. What does the wet laundry or wash cloth feel like before it is hung up? Wait a couple of hours and check it again. What does it feel like? Wait a couple of more hours. What does it feel like? What happened? (Evaporation)
Experiences of evaporation are so common that you probably take them for granted. If your child spills a little water on his shirt, wait and discuss what happened to the spot. Or when getting out of the shower or a tub your child leaves a little puddle of water on the floor. When he returns later, point to that same spot. Where’d the puddle go? Your daughter gets out of the shower with wet hair. What will happen to it? Will it stay wet? Your son paints a picture with watercolors, and later the paint is dry. Where did the water go? Encourage your child to express his own ideas about where the water went. These are opportunities to reinforce the concept of evaporation, what it is and how it fits in the water cycle. Having said that, if your child does not want to use the term evaporation, no problem. She’s heard it. It’s the concept and a general idea of water vaporizing that counts.
Do you have a small hand mirror? Invite your child to breathe on it. What happens? The air in our lungs also contains water vapor. When we breathe onto the mirror, the water condenses out. Try it outside during hot or cold weather, or place the mirror in the freezer for a brief time. What happens? Condensation will depend on temperature.
Look at that mirror in the bathroom after a hot shower. What happened? (Tiny, tiny drops of water are in the air as steam and when they hit the cooler mirror, they condense into bigger droplets). Note that the white mist we call steam is made of tiny, tiny condensed droplets of liquid water that originated as water vapor.
On a hot humid day, take a glass of ice water outside. What happens? (Water molecules in the air as water vapor condense out onto the surface of the cold container and collect as tiny droplets that we see). This won’t work so well if you live in an area where the air is very dry.
Pour about ½ cup of hot water in a jar. On top of that jar, place a metal measuring cup containing ice cubes and a little water. Now watch the bottom of the measuring cup. What happens? This a replication of cloud formation, or water vapor rising from the hot water and coming in contact with cooler air and then condensing out. See Step 4 above. Water transforms from a vapor to liquid (or ice or snow depending on the temperature).
Here is an interesting desalination experiment. Pretty involved, but worth the time if you have a child who might be ready and is invested in the concept of the water cycle.
You can also show demonstrate how the oceans got salty by filling a jar with water and stirring in a little salt. Let your child taste it and write down what she thought. Wait until half of the water has evaporated away and taste it again. Allow more to evaporate and taste again. (The water should now be 4 times as salty as the original). When water evaporates into water vapor it leaves any dissolved material behind.
Create a mini cloud. Place a dry sponge over a bowl or cup. Have your child add a drop of water at a time to the sponge (the cloud). Count the drops of water added until the sponge cannot absorb any more water and starts to leak it out (rain). This is a simulation of a cloud, but talk about how the sponge/cloud takes on more and more water until it is saturated and starts to release the water it can no longer hold.
Create water run off systems. Where does water like to flow (downhill)? What factors could affect what happens to water after it reaches the ground? That is, what may help or prevent water from flowing versus being absorbed? Walk around during a rainstorm. Where is water flowing (over concrete or asphalt or down a hill, or over dirt), where is it collecting (in puddles on flat areas or where there are indentations), where can you not see the movement of the water (depends on the vegetation such as grass or a forest)? Water flow depends on the rate of rainfall, the topography or shape of the land, soil conditions, vegetation, temperatures, and how much urbanization there is (think pavement, roofs and drain pipes).
If your child has some awareness of water flow, invite her to create hills, or river beds in the sand box or the back yard. She may need different types of dirt to really get at the question of where does water go, as some kinds of dirt will absorb the water (sand), while others (clay) will allow it to drain off. You can invite her to also consider lining waterways with pebbles or rocks that should help to keep the water flowing. So, if you have a pile of dirt, a kid who is happy playing in dirt, and a water source (a hose or bucket), build a hill, add some “rain” and watch the water flow. Make predictions about what path the water might take. Was stuff carried off the hill as the water formed a river? Was there only one river, or larger and smaller rivers? Rinse and repeat, as each hill and the addition of water will produce a different result.
Explore how water comes into your home. Does it come through pipes? What do those pipes connect to? More pipes or a well?
You may now want to also discuss sewage treatment.
As part of this discussion, look at the waste that collects on those drains along the side of the street, or plastic bottles, trash, and cigarette butts. Yuck! The water flowing into drains, either the drains in our homes or along the side of the street, will end up back in our water supply. Talk about how to dispose of waste properly so as to protect this finite natural resource that is water.
Studying acid rain is another extension of this basic topic.
Here is a link to start with: http://www.clean-air-kids.org.uk/acidrain.html