Snow Water Equivalent and Snow-to-Liquid Ratio

When talking about snowpack, hydrologists usually express density as the depth of the pack versus the depth of the water that would be produced if the snow were melted. The depth of water produced if a snow cover is completely melted on a horizontal surface is known as the snow water equivalent or SWE. For example, 10 depth units of snow with a liquid equivalent of 20% will melt and become 2 units deep.

Water yield based on snow depth and percent water equivalent

This can also be expressed as a unitless ratio of snow depth to liquid depth, or the snow-to-liquid ratio (SLR). In the example above, there are 10 depth units of snowfall compared to 2 depth units of liquid. This means the SLR is 5:1.

Water yield based on snow depth and snow-to-liquid ratio

Here are some examples of typical snow-to-liquid ratios for various situations. Fresh fallen snow with generally calm winds, and temperatures below freezing has a water equivalent content of about 5%, which comes out to an SLR of 20 to 1. In some cases, this could actually be a lot higher than 20 to 1. We can see 40, 60, or even 80 to one ratios at times. As snow starts to settle, warm, blow, or a combination of the three, the SLR decreases as the snow water equivalent content increases. This is shown for several conditions in the chart below.

Table of snow type and its typical temperature, water equivalent content, snow-to-liquid ratio conversion factor and snow-to-liquid ratio.

SLR Calculation

Snowpack that is 40 depth units high melts into a volume of water that is 2 units high.

The volume of snow shown on the right side in the image above is 40 units deep. We melt the snow and it is now 2 units deep. What is the snow-to-liquid ratio? (Choose the best answer)

The correct answer is d.

40 depth units to 2 depth units reduces to 20:1.

SLR Calculation 2

It is the first snow of the season, and 50 units of snow just fell over your area. The SLR has been reported to be 5:1. How much liquid water would be present if we melted all the snow? (Choose the best answer)

The correct answer is b.