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## WHAT IS IT?

This is an interactive simulation that models the water cycle. It aims to illustrate how relative humidity and the temperature of air, mountain, land, and lake affect the movement of water molecules. This model represents the following five phases of the water cycle: evaporation, condensation, precipitation, surface runoff, and infiltration.

Water is one of the most important element on Earth that is necessary to sustain life. All living organisms need water to survive. Also, learning how water can be made available for consumption helps us understand how we can be responsible in managing our water resources. Therefore, it is important to educate every generation on what causes the water cycle and how it works.

In order to understand the concept of water cycle, one must have knowledge of how the Earth’s gravity pulls objects toward its center and how the sun causes heat on Earth. This simulation will potentially help the user to describe and reason non-numerically about the factors that affect the flow of the water molecules in the cycle. The user will observe the behavior of the water molecules while changing the relative humidity and temperature (air, mountain, land, and lake) parameters.

## HOW IT WORKS

### How does Water Cycle work?

Water vapors (orange dots) evaporate from the lake (light blue curved shape) and rise into the sky (blue background). The occurrence and speed of evaporation vary depending on the temperature of the lake. As the water vapor moves into the sky, the cloud (white cloud) forms. This cloud forms by accumulating the water vapor which cools off during evaporation. Then, the cloud is blown by the wind towards another place, such as the mountain (triangular shape). Then the cloud appears darker (dark cloud) and releases rain (ticks) or snow (white dots) while it slowly disappears (growing smaller).

The precipitation in the form of rain, snow or a mixture of rain or snow varies depending on the percentage of humidity and the temperature of air, mountain, land, and lake. These temperatures are mainly influenced by the sun (yellow object appearing in the sky), gases, and other things.

On top of the mountain, there are existing snowcaps (white triangular shapes). The melting of the snowcaps and precipitation causes water to runoff (flowing of blue dots from the top of the mountain) towards the lower surface of the Earth (green or white plain). Similar to precipitation, the occurrence of surface runoff depends on the temperature of the mountain.

Meanwhile, the Earth's surface (plain on the lower ground) is filled with plants (turns green) or covered with snow (turns white) depending on the temperature of the land. Underneath the ground surface, the water (ticks) infiltrates. The occurrence of infiltration varies depending on the temperature of the land.

Then, the water that is accumulated on the Earth's surface (including lake, ponds, and oceans) goes back into the sky in the form of water vapor. Similar to the other phases of the water cycle, the temperature of the land, lake, pond and ocean mainly influences the movement of the water vapor to rise into the sky. Note that water evaporates at any temperature but of varying quantities.

There are other attributes that influence the water molecules to move around the Earth, such as gravity, speed of the wind, area of the vegetation, elevation of the land, and population of living things but these are not illustrated in this simulation. Also, we did not include all the water cycle phases, such as evapo-transpiration, in which the water molecules transpired by plants, animals, and human beings evaporate into the sky. Future development of this simulation may include more phases and attributes.

### How does the model work?

There are several attributes that influence the water cycle. In this model, only the following factors are illustrated:

Sun - emits energy that heats up the Earth's water, air, land, and atmosphere.

Relative Humidity - the amount of water vapor present in air. This is expressed as a percentage of water vapor or moisture in the air compared to how much the air can hold at a particular temperature. In this model, the values of the relative humidity vary from 0% to 100%. In a natural environment, relative humidity has never dropped to zero percent because water vapor is always present in the air even on the smallest quantity. A reading of 100% relative humidity implies that the air is completely saturated with water vapor and can no longer hold more water vapor. The possibility of precipitation can occur anytime from 1% to 100% humidity.

Temperature (air, mountain, land, lake) - measures how hot or cold the air or surface (mountain, land, or lake) is. In this simulation, the values for the temperature can vary from 0 to 100 degrees Fahrenheit (°F). Water molecules begin to freeze when the temperature falls below 32°F. Otherwise, water molecules remain in their liquid or gaseous state. In a natural environment, water begins to boil at 200°F depending on the altitude, but this is not included in this model.

Water vapor - the gaseous (invisible) state of water molecule. Water vapor in the atmosphere serves as the raw material for cloud and rain formation.

Cloud - forms during condensation and is made of tiny drops of water in the form of liquid or ice. Cloud is a vital part of precipitation as it brings water molecules in the form of rain or snow.

Rain - is a liquid water falling visibly from the clouds.

Snow - ice crystals formed from frozen water vapor and is falling from the clouds in light white flakes.

Mountain - a higher elevation of the Earth's surface.

Earth's surface - surface of the Earth that changes into green if it is filled with plants and other green vegetation, or white if it is covered with snow.

## HOW TO USE IT

Reset button - sets up the background with white cloud forming above the lake and dark cloud pouring rain above the mountain. Trees, grasses, and animals will also vary upon clicking this button. At the same time, the following parameters were set with initial values: Relative humidity - 70%; Air Temperature - 45; Mountain Temperature - 33; Land Temperature - 60; Lake Temperature - 55.

GO button - turns black and runs the model.

Relative_humidity slider - changes the percentage of humidity from 0% (left) to 100% (right)

AirTemperature slider - changes the temperature of the air from 0°F (left) to 100°F (right).

MountainTemperature slider - changes the temperature of the mountain surface from 0°F to 100°F.

LandTemperature slider - changes the temperature of the land surface from 0°F to 100°F.

LakeTemperature slider - changes the temperature of the lake surface from 0°F to 100°F.

ticks slider - changes the speed of the simulation. The speed of the simulation can be adjusted into either slower (left) or faster (right) pace. (The ticks don't seem to mean anything besides showing that the simulation is on the GO).

The simulation runs until the GO button is clicked again and returns into grey color.

## THINGS TO NOTICE

Notice the changes on the following features:

Rate of water vapor and how it depends on the lake temperature.

Form of precipitation and how it is affected by the air, mountain, land temperature.

Earth's surface and how it relates to the land temperature.

Water runoff and infiltration and how those relate to mountain and land temperature.

## THINGS TO EXPLORE

1. Manipulate the sliders and identify the factors that influence evaporation. Note that you need to click on Reset! and go before you start exploring each slider.

2. Manipulate only the air temperature and the land temperature to make the precipitation to be in the form of snow. In what conditions of the air temperature and land temperature will release more snow?

3. What conditions will STOP the water runoff from the surface of the mountain?

4. In what land temperature will infiltration occur?

5. “The less precipitation the more runoff. The more runoff the more infiltration. So, the less precipitation the more infiltration.” Is this statement true? If not, correct it.

## EXTENDING THE SIMULATION

Consider other features such as:

Wind direction and speed that influence precipitation.

Evapo-transpiration from plants, animals and human beings.

Water accumulation under the surface of the Earth.

## CREDITS AND REFERENCES

Lee, T. D., Jones, M. G., & Chesnutt, K. (2017). Teaching Systems Thinking In The Context of the Water Cycle. Research in Science Education, pp. 1-36, (URL: https://doi.org/10.1007/s11165-017-9613-7).
https://pmm.nasa.gov/education/lesson-plans/exploring-water-cycle

https://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-water-cycle

https://pmm.nasa.gov/education/sites/default/files/videos/A_Tour_of_the_Water_Cycle.mp4

## HOW TO CITE

If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.

For the simulation itself:

ACMES Group (2018). NetLogo Water Cycle simulation. Assimilating Computational and Mathematical Thinking into Earth and Environmental Science. Montclair State University, Montclair, NJ.

Please cite the NetLogo software as:

* Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

## COPYRIGHT AND LICENSE
Copyright 2018 ACMES Group at Montclair State University
This work is licensed under the GNU GENERAL PUBLIC LICENSE V3. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. To view the details of the license, you can visit https://www.gnu.org/licenses/gpl.html.

Acknowledgment
This research is supported through a STEM+Computing grant from the Division of Research on Learning of the National Science Foundation (# 1742125).