How Changing Snowmelt affects Water in the Western U.S.

By Water Science School

In this activity students will investigate how snowpack acts as a natural water storage system and how changes in snow accumulation and melt timing affect streamflow and water availability in the Western United States.

How Changing Snowmelt affects Water in the Western U.S. - Lesson Plan [PDF]

From Snow to Flow - Data Visualization

Sources/Usage: Some content may have restrictions. View Media Details

How Changing Snowmelt affects Water in the Western U.S.

Objective:

Students will investigate how snowpack acts as a natural water storage system and how changes in snow accumulation and melt timing affect streamflow and water availability in the Western United States. Using a USGS interactive visualization and real monitoring data, students will analyze trends, interpret hydrologic variables, and evaluate downstream impacts on people and ecosystems. This activity aligns with Next Generation Science Standards for high school science education.

Next Generation Science Standards (NGSS) Standards:

DCIs: ESS2.C: the roles of Water in Earth’s Surface Processes, ESS2.D: Weather and Climate, ESS3.A: Natural Resources, ESS3.D Global Climate Change
CCCs: Cause and effect, stability and change, systems and systems models, Scale, Proportion, and Quantity
SEPs: Developing and using models, analyzing and interpreting data, constructing explanations and designing solutions, engaging in argument from evidence.

Key Terms:

Snowpack - Accumulated snow that stores water during the cold season in mountainous regions.
Snow Water Equivalent (SWE) - The amount of liquid water contained in snowpack; used to estimate meltwater volume.
Melt Timing (SM50) - The date when half of the season’s maximum SWE has melted, measured as days since October 1.
Soil Saturation - The amount of water held in soil, influencing infiltration and runoff.
Streamflow - The volume of water moving through a stream or river over time.
Water Availability - Combination of how much water is physically accessible (water quantity) and whether that water is safe to use (water quality).
Water Year - A 12-month period from October 1 to September 30 used by hydrologists to track seasonal water processes.

Think - Individually

Snowmelt contributes a lot of water during spring in a river in Banff, Canada

Sources/Usage: Some content may have restrictions. View Media Details

Much of the water in the western United States comes from snowmelt.
•    Why might snow be considered a “frozen water tower”?
•    What could happen if snow melts earlier than usual?
•    Who depends on this snowmelt water downstream?

Using the following data visualization page from USGS VizLab to complete the activity.
https://labs.waterdata.usgs.gov/visualizations/snow-to-flow/index.html#/

Review - Pair or Group Discussion

After reading the passage on the page, ask students to define or discuss the following in pairs or groups. After reading the introduction text on the page, ask students to define or discuss the following in pairs or groups.

How do high elevation mountains store water through the cold season.
Why is the timing of snowmelt just as important as the amount of snow?
How does snowmelt connect soil, streams, ecosystems, and human water use?

Ask students to review the following snow-to-flow processes described in the visualization:
•    Soil saturation affects whether meltwater infiltrates or runs off
•    SWE determines how much water is available to melt
•    SM50 shows when snowmelt happens
•    Streamflow reflects how snowmelt moves downstream

1. How do these variables work together as a system to control water availability?

Analyze and Reflect - Answer individually or in small groups

Comprehension

Why does snowmelt produce a large pulse of streamflow in spring?
How do warmer temperatures affect both snow accumulation and melt timing?
Why might low snowpack combined with early melt lead to reduced water availability later in the year?
How could earlier snowmelt increase risks of drought, wildfire, or flooding?

Data Interpretation - Students should analyze the interactive graphs on the visualization webpage to answer the following:

Line graph showing streamflow and SWE, with shaded peaks in blue and grey.

Sources/Usage: Public Domain. View Media Details

* Check the axis labels carefully and use the available chart tools to reorganize the data to determine your answer.

What does high peak SWE with late SM50 indicate about spring streamflow?
What happens to streamflow during low peak SWE and early melt years?
Compare Water Year 2011 and 2012. How did differences in snowpack affect streamflow downstream?
How does elevation influence snow accumulation and melt timing?
Why do hydrologists use a water year instead of a calendar year?

Challenge - Design a Water Management Response - Planning for Changing Snowmelt

Your community relies on snowmelt-fed rivers for drinking water, agriculture, and ecosystems. Recommend three actions water managers could take to adapt to changes in snowpack or snowmelt timing.
Students should justify their recommendations using evidence from the visualization and readings.

Applied Exploration

How Does the Amount of Snow Affect Streamflow?

Objective: Students will model how different amounts of snowpack (Snow Water Equivalent) affect:

The volume of runoff
The timing of runoff
The duration of water availability

Students will use this physical model to explain how changes in snowpack influence streamflow and downstream water supply.

Materials (per group of 3–4 students):

3 shallow trays or aluminum baking pans
Soil or sand (1–2 inches deep in each tray)
Ice cubes or crushed ice
Measuring cup (for meltwater collection)
3 clear containers (to catch runoff)
Timer or stopwatch
Ruler or scale (optional, for measuring ice)
Paper towels

Set Up

Each tray represents a watershed with the same slope, soil, and temperature, but different snowpack amounts.

Tray Conditions

Tray	Snow Amount (Ice)	Real-World Scenario
Tray A	Small amount (5 ice cubes)	Low SWE / dry winter
Tray B	Medium amount (10 ice cubes)	Average snow year
Tray C	Large amount (20 ice cubes)	High SWE / snowy winter

(Teacher note: Emphasize that ice amount = SWE, not snow depth.)

Procedure:

Prepare the Watersheds
1. Fill each tray with the same amount of soil.
2. Tilt each tray slightly using books so water can flow downhill.
3. Place a collection container at the bottom of each tray.
Add Snowpack (Ice)
1. Place the correct number of ice cubes evenly across each tray.
2. Ensure ice placement is similar in all trays (spread out, not stacked).
Simulate Snowmelt
1. Start the timer as soon as ice begins to melt.
2. Observe for 15–20 minutes.
3. Do not add water, melting occurs naturally at room temperature.
Observe and Measure, Students should record
1. Time when runoff first appears
2. How fast water flows
3. Total volume of runoff collected
4. How long runoff continues

Data Collection Table (Student Handout)

Tray	Ice Amount	Time to First Runoff (min)	Total Runoff Volume (mL)	Runoff Duration (min)
A	Low
B	Medium
C	High

Discussion Questions:

Observations

Which tray produced runoff first?
Which tray produced the most runoff?
Which tray produced runoff for the longest time?

Interpretation

How does increasing snow amount affect total streamflow?
How does snow amount affect how long water is available?
Which tray best matches:
1. High peak SWE + late SM50?
2. Low peak SWE + early SM50?
How does this experiment help explain:
1. Reduced summer water supply after low snow years?
2. Why is snowpack often called a “frozen reservoir”?

Optional Follow up:

Repeat the experiment with one of the pans with the now wet soil/sand.
1. Describe the impact of soil moisture on runoff.

Helpful Links:

https://labs.waterdata.usgs.gov/visualizations/snow-to-flow/index.html - /

https://www.usgs.gov/water-science-school/science/snowmelt-runoff-and-water-cycle