Columbia River Calling

Basin Maps, Part 7 – Climate Change and Snow in the Basin

Both the British Columbia Decision and US Regional Recommendation note that climate change is a critical challenge that the Columbia River Basin faces today and will face in the future.  Today’s post serves as part seven of the Basin Maps series as well as the second in a series of posts counting down to the 50th anniversary of the Columbia River Treaty.  It provides a brief look at what climate change means for snow in the basin.

Description: This map displays the trends in the snow water equivalent (SWE) measured on April 1 for 1950 to 1997.  SWE is the amount of water contained within the snowpack (the amount of water you end up with if you melt the snow). Mote et al. 2005 offer the following description of their map:

“Linear trends in 1 Apr SWE relative to the starting value for the linear fit (i.e., the 1950 value for the best-fit line) at 824 snow course locations in the western United States and Canada for the period 1950–97, with negative trends shown by red circles and positive by blue circles…”

Source: Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier. “Declining mountain snowpack in western North America.” Bulletin of the American Meteorological Society. 86 (2005): 39-49.

Date: 2005

What is unique: The map illustrates how snowpack, as measured by SWE on Apr 1 is declining in most of the measured locations in the basin. It is a sobering indication of the water challenges we face today and will continue to face in the future.

What’s missing: The map is older and only includes data through 1997.  But I selected it because it was one of the few maps that displayed trends in the entire basin.  Most maps focused on either the American (1955-2013) or Canadian (1956-2005; Figure 12 on page 146) portions of the basin.

Why does climate change matter in Columbia River Treaty reviews?

Climate Change: The need to address climate change is an area of agreement for the US and Canada as they review the Treaty.  Therefore, it may be a unifying issue as the two countries work to define Called Upon or potentially modify the Treaty.

Snow: Snow serves as a natural reservoir of water in much of western North America, including the Columbia River Basin. We use the snowmelt to provide water in the dry summer months.  If precipitation shifts from snow to rain we will lose that storage and the hydrograph will also shift, with higher flows earlier in the year (a trend we are already seeing).  If we want to maintain the current hydrograph our river management operations will also need to change and we will need to storage more water by other means.

If you would like to learn more about climate change in the Columbia River Basin here are some great resources:

Bonus Maps!

This first map depicts the impact of a declining or earlier melting snowpack on streamflow.

This second map by Nolin and Daly (2006) highlights “snow at risk” in the US portion of the basin. Figure 3 from their paper shows snow cover classification using a rain–snow threshold of 0°C with a-risk snow in red.


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