The amount of water within the snowpack can vary greatly over time and space. Sp

ID: 153330 • Letter: T

Question

The amount of water within the snowpack can vary greatly over time and space. Spatial and temporal variability of snow water content is caused by the variable proportion of snow ingredients: frozen water and air. Snow water equivalent (SWE) is the amount of water contained in a snowpack. SWE is expressed as a percent. For example: Visualize an enclosed courtyard filled with five feet of snow with a SWE of 10%. If all the snow suddenly melted, it would create a pool of water 6 inches deep (10% of the snow that once filled the courtyard, or 5 feet × 10%). SWE varies across continents. Warm air masses hold and deliver more moisture than cold air masses. The higher average air temperatures in coastal mountains produce snowfall with higher moisture content and higher SWE. Conversely, the colder mountains of continental interiors produce “light and dry” snow with lower water content and lower SWE. As temperatures decrease with elevation, the SWE usually decreases was well. Snowpack density also increases during the winter as the snow settles under its own weight and undergoes freeze-thaw cycles. The changing density increases the SWE. For example, snowpack densities vary between 7–30% in the winter, and increase to 25–45% in the spring as the snow settles under its own weight. Identify the correct statements below regarding the principles of snow water equivalent and snow density.

The amount of water produced by snowpacks of equal depths at two locations will be the same despite any air temperature differences.

Question 2 )

Temperature is an important control on snow water equivalence. How has temperature changed between 1920 and 2000 in the northwest US? Refer to Figure D1 below that shows air temperature gauging stations. The size of the circles relates to the magnitude of temperature changes at points in this region. Locations with blue circles experienced decreasing temperature. Locations with red circles experienced increasing temperature. Select the statement below that correctly describes the trend of temperature in this region.

Temperature has become cooler during this period, especially along the western coastline of these states.

The Rocky Mountains are far inland and the Cascade Mountains are nearer to the coast. The snow water equivalent of the Rocky Mountains is probably lower than the Cascade Mountains based upon the location of these ranges. The water content of snowpack is the water equivalent of snow. The amount of water in snow is a constant value.

The amount of water produced by snowpacks of equal depths at two locations will be the same despite any air temperature differences.

Question 2 )

The scattered locations of temperature indicate that are no detectable temperature trends during this time. Temperature decreased by 3.6 degrees F throughout the area depicted in the figure. Temperature increased by a minimum of 1.8 degrees C during this period throughout the area depicted in the figure. Temperature is warming at most locations. The locations in the lower-right of the figure are warming less than the western states.

Temperature has become cooler during this period, especially along the western coastline of these states.

Explanation / Answer

Question - 1

It is true because coastal mountains such as Cascade Mountains have higher average air temperatures that produce snowfall with higher SWE, where as the inland Rocky Mountains produce snow with lower SWE.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The water content of snowpack is the water equivalent of snow- CORRECT.

Snow water equivalent (SWE) is the amount of water contained in a snowpack.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The amount of water in snow is a constant value - INCORRECT.

The spatial and temporal variability of the amount of water in snow is very high and it is caused by the variable portion of frozen water and air.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The amount of water produced by snowpacks of equal depths at two locations will be the same despite any air temperature differences- INCORRECT.

At two locations of equal depths, the amount of water produced by snowpacks will not be the same because the Snowpack density varies all the time.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Question -2

The scattered locations of temperature indicate that are no detectable temperature trends during this time - INCORRECT.

Since there are considerable number of Red dots indicating an increasing temperature trend, the above statement is not correct.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Temperature decreased by 3.6 degrees F throughout the area depicted in the figure - INCORRECT.

The temperature decrease of 3.6 degrees F is indicated by the largest blue dot which is absent in the given map.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Temperature increased by a minimum of 1.8 degrees C during this period throughout the area depicted in the figure - INCORRECT.

There are significant number of smallest Red dots that indicate that minimum temperature increase is of 0.9 degrees F and not 1.8 degrees.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Temperature is warming at most locations. The locations in the lower-right of the figure are warming less than the western states - CORRECT.

This statement is correct because there are clearly more Red dots representing warmer temperatures in the western states when compared with those on the lower-right.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Temperature has become cooler during this period, especially along the western coastline of these states - INCORRECT.

Temperature has rather become warmer during this period (1920-2000), especially along the western coastline of these states.