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Transcript
P R O J E CT G U T S
W AT E R R E S O U R CE S
Mountain Snowmelt Model
in StarLogo TNG
Overview
This model simulates snow melting off of the top of high mountain ranges.
Snowpack is a vital source of water for many parts of the world, and is especially
important in the Southwest and Western states which depend upon river flows
generated from snowmelt in order to satisfy their water needs.
In this model, snowmelt is simulated by creating an elevated surface, which is
then covered in snow. When the model is running, and incoming solar radiation
produces heat which melts the snow. The water then flows off the mountain,
following the terrain until it lands in the surrounding flat basin where it is assumed
to either enter the groundwater or evaporate.
One of the minor dynamics at play in this model is ice albedo feedback, which
is elaborated upon in its own writeup and model. Depending on the terrain the
model plays out on, albedo effect can impact the results of the model in
different ways.
The Model
This model simulates a mountain range during and after a melting period.
Incoming solar radiation strikes the ground and generates heat, which then
melts the snowpack generating water. The water then travels downslope and
evaporates (or enters the groundwater) at the base of the mountain.
There are five breeds in this model: a sun, solar radiation, reflected solar
radiation, heat, and water. The sun generates solar radation which travels
downwards. If solar radiation hits a white “snow” patch it reflects back up as
reflected radiation. If solar radiation hits brown ground, it turns into heat. Heat
moves around the world randomly. If it runs into snow it melts it, which
generates water which then runs downhill.
While the premise of the model is simple, the actual code involved is somewhat
intricate. Instructors attempting to build this model from scratch with their
students are advised to give plenty of time.
An easier implementation of this model in the classroom is to deconstruct the
model and then implement possible changes, elaborated on in the “expanding
the model” section at the end of this document.
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Procedures
Breeds
There are five breeds in this model:
sun, solar energy, reflected energy,
heat, and water. Since the sun,
solar energy, and water can be
easily depicted as spheres and the
heat agent will be hidden, make
the sphere the default shape for all
agents.
Setup
Setup is a complicated procedure in this model and works in three parts:
1). First, a “shared
number” variable is
used to keep track of
the amount of snow in
the world.
A clear everyone block
is used to preserve
whatever terrain we
might produce.
Set snow 0 is used to set
the initial value of snow
to zero, which
effectively resets any
plots and monitors.
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INTRODUCTION
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2). As with the ice albedo model, we create a temporary sun which will set up
the snow. The sun begins in the lower left corner, and faces 0 degrees so that it
can procedurally visit all of the patches. The sun then visits each patch testing to
see if the patch it is on is higher than patch height 0. If it is, the sun stamps the
patch color white and increases the count of snow by 1. If patch height is 0, the
sun stamps it brown and moves on. “Set x xcor + 1” is used to move the sun from
the left to the right.
3). Next, we create the sun in the sky.
Create one sun and have it set altitude 100,
set xy 0, 0 (high up in the middle of
SpaceLand) and set its size to 5 and color to
yellow. This will give the impression of the sun
hanging high in the sky producing solar
energy.
Lastly, reset clock is used to clear any
graphs or monitors.
Make Solar Energy
The “Make Solar Energy”
procedure is used to rain down
solar energy from the sun onto
SpaceLand.
The sun hatches, and “Set Breed:
Breed Solar Energy”, “set color red”
“set size .25” “set heading random”
are used to generate the particles
of solar energy coming from the
sun.
“set xy” is used to spread the solar
energy so that it has a chance to
land on every patch. “random 101
– 51” is used to cover the entire
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space.
Solar Energy Step & Reflected Energy Step
Solar energy step
tells the solar
energy to rain
down, and what to
do when it strikes
the ground.
To rain down from
the sky, solar energy
simply moves down
one step if its
altitude is greater
than 0.
If it is on the ground,
solar energy step
runs two checks:
If it hits patch color
white, it hatches a
reflected energy
breed. This
reflected energy sets its color to orange, and the original solar energy dies.
Else, (if it does not hit snow), it hatches a heat agent which then sets its heading
random 360 and is hidden. The original solar energy then dies.
Reflected Energy Step
Reflected energy step is simple: it heads straight
up from its original position. If it reaches an
altitude of 75, it dies (assumed to be reflected
back out into space).
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INTRODUCTION
Heat Step & Collision
Heat step tells heat
agents how to move
around the world.
Starting from their origin
facing a random
direction, heat moves
forward one step each
iteration.
If the heat steps on a
patch that is on the
mountain AND white,
the heat agent stamps
the patch brown (melts
the snow), decreases
the amount of snow
(“inc snow -1”) and
hatches a new agent.
The new agent then sets its breed to water, color to blue, size to .2, and
because the heat was previously invisible, “show agent” is used to make the
new agent visible again.
The heat then dies.
Heat Collision
The heat collision block makes heat
agents that collide with other heat
agents set both agents’ headings in a
random direction.
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Gravity (water procedure)
Gravity tells newly created water
agents how to flow downhill.
First, the water agent tests to see
if it is facing uphill. If it is, it turns to
face a new random direction.
If the water agent is facing
downhill (slope is less than zero), it
moves forward one step and
turns its heading random 360
again.
If the water encounters a white
patch on the way down, it
stamps the patch brown and
decreases the amount of snow in
the world.
Finally, if water is on a flat section,
it dies (is assumed to evaporate
or seep into groundwater).
Runtime/Forever
The forever block calls each of the procedures:

The sun makes solar energy.

Solar energy moves down and interacts
with the terrain.

Reflected energy radiates back up.

Heat moves around an interacts with the
snow.

Water flows downhill and interacts with
snow.
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INTRODUCTION
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Monitors
In this model we
keep track of
several different
variables:
Reflected
Energy: This
graphs the ratio
of energy that is
reflected out
into space
compared to
energy
incoming. As ice
decreases, so does the amount of reflected energy.
Heat: This keeps track of how much heat is in the world. Note that there are no
heat sinks in this model, so heat continually increases.
Snow: This monitors the amount of snow remaining in the world.
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Running the Model
First, raise the level of the ground using the Create Mound On Region tool in the
Edit Terrain toolbox. Refer to figures 1-4 below.
Figure 1
Figure 2
Figure 1
Figure 3
Next, click Setup and the
mound will be covered with
snow.
Figure 4
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INTRODUCTION
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Finally,
click
on
Forever and watch as
incoming solar energy
produces heat, which
melts the snow starting
at the base of the
model.
Note the monitors at
the bottom: Snow
pack decreases while
heat ever increases.
The
amount
of
reflected
energy
largely depends on
incoming energy randomly striking snow. This is represented as fluctuations, but
the overall trend is a decreasing amount of reflected energy as the snowpack
melts.
Expanding The Model
This model is a vastly simplified version the actual dynamics that occur on a
snowpacked mountain. There are many ways to expand it to make it more
realistic, or even to have fun and play around with it.
1). In the real world, the rate of snowpack melting is partially greatly determined
by the reflection coefficient or albedo of the snow. Many factors can influence
albedo, including dust in the air landing on snow. How might you simulate dust
that lands on the snow, decreasing the albedo?
2). In the base snowmelt model, altitude does not affect the behavior of the
heat agents in any way. In the real world, however, altitude and temperature
are closely correlated. How might you model this phenomena? Hint: Agents can
tell the height of the patches they are on, as well as the slope of those patches
in front of them.
3). Water in this model does not flow very realistically. Is there a better way to
make water trickle down the mountain? Perhaps have an agent remember its
heading and slope ahead, and compare those numbers to a sample of the
slopes around it.
4). Snowmelt over eons is one of the major factors in the erosion of mountains.
Without the annual snowmelt, mountains would look very different than they do.
How might you simulate erosion? (hint: agents can “stomp” terrain down or
“yank” terrain up).