Snowmelt triggered by the heat wave wiped out any benefit that higher-than-average snowpack levels might have held for river flows in the summer dry season.
If you were anywhere in the high country of the North Cascades during the heat wave, you probably noticed how quickly the snowpack was melting out. Creeks and rivers swelled. The three upper forks of the Nooksack River were surging during those days and a few days to follow. It’s a different story, however, for the Lower Nooksack tributaries (such as Bertrand and Fishtrap creeks), which are fed by wetlands in Canada, rain, and groundwater sources. The abnormally dry spring has reduced flows more significantly than normal.
A dry spring plus a heat wave could spell trouble for Nooksack watershed fish and farms. First, let’s focus on snowpack in the North, Middle, and South Forks of the Nooksack River. On June 1, snowpack was slightly above average, ranging from 8 inches at Elbow Lake (3,000 feet of elevation — feeds into the South Fork), 53 inches at the Middle Fork Nooksack (5,000 feet of elevation), and 15 inches at Wells Creek (4,000 feet of elevation — feeds into the North Fork).
Elbow Lake and Wells Creek were snow-free on June 16 and the Middle Fork had 34 inches. The day before the heat wave on June 26, the Middle Fork recorded 12 inches of snow. June 27 was 8.9 inches, June 28 was 5.1 inches, June 29 was 1.9 inches, June 30 was .2 inches, and it was snow-free on July 3.
Looking back at last year which was overall a fairly average snowpack and precipitation year, these same areas were snow-free a few days later — July 9 for the Middle Fork. In other words, the snowmelt triggered by the heat wave wiped out any benefit that higher-than-average snowpack levels might have held for river flows in the summer dry season.
Note that these sites in the Nooksack watershed (where the Natural Resources Conservation Service measures snow levels) are not located on any glaciers.
Higher flows picked up a few days earlier than normal this year as compared to 2020 for all three forks. What is especially notable is the South Fork flows have already dropped off from melting snowpack — this did not happen until late July in 2020. It will be interesting to watch flows on the Middle and North forks later in the year to see whether melting glaciers are contributing to flows.
During the heat wave, water temperatures in the South Fork were 10 °F above the median clocking in at over 60 °F at one point. Water temperatures above 68 °F are lethal for salmon. Days after the heat wave, water temperatures have dropped back close to the median in the South Fork. Hopefully, fall Chinook returning to spawn in the next few weeks will not be impacted.
Lower Nooksack Tributaries in Trouble
Bertrand Creek hit the 10 cubic feet per second (CFS) mark in mid-April for 2020 and 2021 (this is early, given the historical median of reaching 10 CFS in mid-May). But, without much late spring and early summer rain, the flows haven’t been able to rebound like we saw in spring 2020, where they hovered around the 10 CFS mark. Aside from a few spikes in 2021 during that same period of time, flows have been consistently below 10 CFS.
Fishtrap Creek looks even worse than Bertrand Creek this year. The USGS discharge graphs are set at different scales in 2021 than 2020. In 2020, flows did not dip below 20 CFS for this time period. Unfortunately, flows have been under 10 CFS from mid June through now.
Many of the Lower Nooksack tributaries serve farms. This is the time of year when farms need water most, and the need to protect crops is only increasing with hotter temperatures. Many of the farms in the area do not have proper water rights and are taking water from groundwater and streams, which will leave less water available for chum salmon when they return to these creeks in the fall. Groundwater is vital for replenishing the Nooksack River’s flows along tributaries that don’t rely on snowmelt. If groundwater levels drop below the bottom of the streambed, many tributaries will not have water to serve fish and wildlife.
Whatcom County’s New Normal
Looking forward, we know that here in Whatcom County we can expect increased temperatures, decreased snowpack, earlier peak streamflows, and more frequent summer droughts. At the current rate of warming, by about 2040, in Washington state, we can expect:
• 38 percent less snowpack draining into rivers and streams.
• The North Cascades glacier area decreased by 56 percent between 1900 and 2009. With the snowpack decreasing, the Nooksack River will become a rain dominant system.
• 23 percent decrease in spring and summer streamflows.
• 67 percent increase in days with temperatures above 90 °F.
Unless aggressive changes are made immediately, we can expect that in the next 30 years, the average year in Washington will be warmer than the hottest year of the 20th century.
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First published on the RE Sources’ website: https://www.re-sources.org/2021/07/washington-drought-the-heat-wave-melted-the-all-the-nooksacks-extra-2021-snowpack/.