Atmospheric Rivers reads and notes

Since northwest Washington State (and more so southwest British Columbia) are experiencing a series of atmospheric rivers (AR), I have been doing a bit of reading/catching up on the subject. On a professional level ARs paly a role in my work assessing geology risk so understanding ARs is important in assessing geology hazards. 

ARs have and continue to receive a lot of attention as they are the cause of much of the large flooding events of the west coastal watershed of North America and are also the source of much of the water in watersheds of the southern portions of the west coastal area. Due to the risk of large floods and the impact to reservoirs, there has and will likely be a continued interest in evaluation and understanding ARs. The most recent flooding in southwest BC and northwest Washington emphasized the importance of this issue. Further, ARs are expected to change with global warming -- there are numerous papers of modeling and climate simulations that indicate changes in ARs over past and present day.  

What follows are a few papers with my own notes and what I thought to be pertinent quotes from the papers themselves.   

Neiman and others (2011) focus on ARs impacts on 4 different western Washington watersheds, the Sauk, Green, Satsop and Queets. They identify some key attributes to ARs that produce floods. 

"ARs were responsible for all floods in these basins during the 30-yr period, even though not all ARs during that period generated flooding. Those ARs that produced flooding typically exhibited two or more of the following attributes: (i) the AR was optimally oriented for orographic precipitation enhancement in a given basin, (ii) the low-level onshore water vapor fluxes into the basin were quite strong, (iii) the AR stalled over the basin, (iv) the melting level was especially high, and/or (v) basin soils were already saturated prior to AR landfall."

The recent AR flooding in northwest Washington and southwest BC had essentially all of the above attributes. 

 A figure from Neiman and others (2011) illustrates the attributions for the basins they evaluated.

Conceptual representation of key atmospheric conditions associated with the top 10 annual peak daily flows observed in four watersheds in western Washington. (a) Offshore composite IWV analysis (cm; green shading >2.8 cm) based on the NARR for the Queets and Green Rivers. Washington State is shaded and labeled. (b) Overland composite low-level wind-flow direction (blue arrows) based on the NARR for the Green and Queets Rivers. See Fig. 3 for details on the base map. (c),(d) As in panels (a) and (b), except for the Sauk and Satsop Rivers and red arrows. (e) Composite NARR-based vertical profile information common to all four watersheds in the low-level onshore flow (bold arrow). The upper and lower horizontal dashed lines mark the observed and climatological melting levels, respectively (the climatological melting level is from Minder 2010). Gray shading represents the layer of weak moist static stability. The black curve depicts the water vapor flux profile.

Baek and Lora (2021) suggest that ARs intensity may increase sooner rather than later relative to other published papers. If their assessment holds true, changes to ARs will come sooner than most other modeling papers suggests:

"Here we use a series of coupled model experiments to show that there was little to no change in mean AR characteristics in 1920–2005 due to opposite but equal influences from industrial aerosols, which weaken ARs, and greenhouse gases (GHGs), which strengthen them. Despite little historical change, the simulations project steep intensification of ARs in the coming decades, including mean AR-driven precipitation increases of up to ~20 mm per month, as the influence of GHGs greatly outpaces that of industrial aerosols." 

Espinoza and others (2018) suggest that ARs will not be as frequent in the future, but may be much more impactful: 

"The projections indicate that while there will be ~10% fewer ARs in the future, the ARs will be ~25% longer, ~25% wider, and exhibit stronger integrated water vapor transports (IVTs) under RCP8.5.

Further works on field experiments, process studies, and model evaluation and improvement (e.g., Guan & Waliser, 2017; Hagos et al., 2015; Payne & Magnusdottir, 2015; Ralph et al., 2016; Wick et al., 2013) need to be undertaken to improve the model fidelity and reduce the uncertainty in the projections."

Gershunov and others (2017) consider the increased trend in AR to have already begun and project the increase trend will continue. They also note that the trend will not be uniform along the west coast:  

"Moreover, a long-term trend expressed broadly in stronger winter AR activity over the U.S. and Canadian west coast (weaker over Mexico) is associated with long-term warming of the western tropical Pacific; the latter SST trend has previously been identified in multiple observational data sets and explained by anthropogenic forcing [Wang et al., 2015]. Long-term precipitation changes over western North America have been very consistent with this trend. This broad increase in AR activity is corroborated by total seasonal IVT version of the analysis, where it is clearly associated with basin-scale ocean surface warming, as well as by a consistent increasing trend pattern in observed precipitation. These results suggest that the increase in IVT projected for the midlatitudes in response to global warming [Lavers et al., 2015] has been ongoing over at least the north Pacific, which calls for an investigation of the role of ARs in the projected enhancement of extreme precipitation over California and the Western U.S. [Polade et al., 2014] as well as a fresh investigation into observed changes already under way."

Rhodes and others (2020) project that the changes in total precipitation in the west of North America will be primarily the result of ARs 

"Changes in precipitation totals are due to a significant increase in AR (+260%) rather than non-AR (+7%) precipitation, largely through increases in the most intense category of AR events and a decrease in the interval between landfalling ARs."

Gershunov and others (2019) also project changes in precipitation specific the watersheds on the west coast. For the the Chehalis River:

"In fact, AR contributions increase in all precipitation bins, with the increases becoming greater at higher intensities, while non-AR precipitation contribution is projected to become more frequent in the drizzle and other low-intensity precipitation categories, and decreasing at higher intensities."

Dongyue and others (2019) did a broad overview of rain-on-snow, a possible contributor to AR flood events (see Neiman and others, 2011 above). Their assessment was not specific to ARs and covered all areas of the US subject to rain-on-snow. Cliff Mass cited this paper in a blog post suggesting that snow melt is a minor contributor to recent flooding after comments suggested snow melt was an additive factor to the recent flooding. However, despite that reference, Dongyue and others (2019) note:  

"It is also clear that a significant portion of floods that occur in basins that drain the west facing slopes of the Cascades and the Sierra Nevada are ROS related."

I do agree that for the recent AR event (November 14-15) rain was the source of the majority of the water in the floods, but even a relative minor snow melt component, say 10 percent, can push a river to a much more consequential flood event.

 Dongyue and others (2019) further note:

"Historically, the contribution of ROS to extreme runoff in the western United States has been greatest in midelevation areas (1,000 to 1,500 m); this “significant influence zone” will shift higher in the future (above 2,000 m). 

This elevation range matches many but not all Cascade watersheds.

The recent AR event in northwest Washington and southwest BC is a preview of what society should plan and prepare for as ARs become more intense with global warming.

Notes on Skagit and Nooksack Flood Levels

An atmospheric river  has been aimed at northwest Washington over the past few days and the rain continues today. A look at river level gages and predictions indicates some serious river flooding. But note too that many small streams have no flow gauges or predicted flood crests will flood as well.

The Skagit River has reached flood stage , but the current predicted flood crest at Mount Vernon will not arrive until tomorrow. The Skagit is a large river watershed and the peak flows take a while to get down to the delta area. Projections are for record flood levels at Mount Vernon.    

The much smaller Samish River also flows out onto the Skagit delta will peak faster with a record peak today. 

Both of these rivers flow out across broad low delta areas with portions of the deltas diked from tidal flooding. The Skagit has very large levees through Mount Vernon. But some over topping may take place. The Samish also has levees, but they will very likely be over topped. Once the delta floods the drainage out of the delta is restricted by the tidal levees -- all that water that spills out of the rivers then has to flow through drainage systems and tide gates.   

The Nooksack River began flooding yesterday. The Nooksack flooding is complicated. At Ferndale the projection is a moderate flood level. 

However, upstream at Cedarville the projection is potential record flood levels. 

Between Cedarville and Ferndale the river flood waters flood out of the Nooksack and into the Sumas River River (everson-sumas-overflow). Hence, the flood levels at Ferndale is somewhat diminished by water laving the Nooksack and flooding into the Sumas River. The border town of Sumas in the Sumas watershed began flooding yesterday.     

The Nooksack River has three forks that converge above Cedarville. This ads another complication to the Nooksack flooding because the timing of each forks peak discharge makes a big difference in the flooding downstream. There will be major flooding in the South Fork valley. 

  

Cedar Boughs

 Evaluating a valley in the Olympics earlier this fall I noted these cropped trees. 

The limbing was not for creating views through the forest, but was a partial harvest of the tree boughs for evergreen arrangements and/or wreaths. The trees in this case are western red cedar. And this was an allowed operation by the land owner. Evergreen foliage is a big business on the Olympic Peninsula and southwest Washington, and unfortunately some of that business is illegal harvesting. It is particularly problematic in young tree stands as the removal of branches and even the tips of the trees destroys the tree plantation. The very fact that the trees above were scaled and limbed (by hand) in the manner they were indicates the value of these products.  

Chicken Eggs

Traveling to a field work site I came across one of the larger egg producers in Washington State. The packaging for the eggs notes that the chickens at this farm are free ranging. Agricultural friends have told me that the egg labeling is accurate. I got to see what a large scale free range chicken operation looks like. Thousands of chickens meandering through open grass fields.   

The farm is Wilcox Farms in the Nisqually River valley. They kindly allowed me access across the farm to assess a site saving me from a rather long bushwhack along rough river bottom land.

Last week I passes by another large egg operation. I observed no chickens at that facility which is consistent with the labeling on the egg packages.

Political Sunday: Snake River Dam Editorials and Sports Radio Goes Political

Snake River Dams Opinion Pieces:

Over the years various newspapers across the Pacific Northwest have put out editorial opinions on the lower four dams on the Snake River and printed guest opinion columns (disclosure - I wrote a guest opinion piece for the Bellingham Herald on the Snake River dams 20 years ago). The Columbian out of Vancouver, Washington published an editorial on the lower four dams (in-our-view-new-approach-is-needed-to-save-iconic-salmon). The editorial suggests breaching the dams "warrants serious consideration". The Columbian included a quote from another newspaper editorial from the Walla Walla Union Bulletin. Part of the quote stated "The water from a free-flowing Snake would flood farms, roadways, homes and even cities." 

Since the initial Walla Walla Union Bulletin editorial, the Union Bulletin corrected the Editorial and has a correction statement at the end stating "The Snake River dams do not provide flood control as previously stated."  

My take-away is that the Columbia Editors do not have a good understanding of the lower Snake River dams, otherwise they would have readily noted that the Walla Walla Union Bulletin statement about flooding made no sense. The Columbian error is somewhat forgivable; the Snake River is far upstream from Vancouver, Washington and one might assume that the nearby by Walla Walla paper would have a better understanding of the lower Snake River. Alas proximity to the dams may be a hinderance to understanding them, and the Union Bulletin editors credibility on this issue should be greatly diminished.    

Fall Back:

Note - I live just a bit south of the 49th parallel and pretty far west in the time zone.  

In my work I drive a fair bit to field sites. I listen to NPR, CBC and sports radio depending on where I am and the time of day or evening. The sports radio folks (KIRO) are generally pretty good at navigating through that political wickets. One of the conversations I heard on sports radio this past week was introduced as a political subject that all red and blue folks could support: a proposed bipartisan bill to allow states to remain on daylight savings sponsored by Washington Senator Patty Murray and Florida Senator Marco Rubio. The radio host was fully supportive of the bill. I support it as well. 

My rationale is that every fall I ease into getting up in the dark as the days grow shorter and sunrise slowly moves later into the morning. By the end of October I am getting up in complete darkness. I am not a fan of getting up in complete darkness, but I got used to it. With falling back an hour I have to restart the process or simply get up earlier (the same time by ignoring the clock all together). All in all getting up in the dark in the winter is not that big of a deal, but the sudden darkness at 5:00 pm is the part of the time switch I find to be very undesirable, and as the winter moves on, the late darkness moves to 4:00. I am on the west side of the time zone - it is even worse for those on the east side. 

Debris Flows, Logging and Marbled Murrlets - Lake Cavanaugh

Lake Cavanaugh is located within the northwest Cascades near the southern Edge of Skagit County. The 2.75 mile long lake was formed by continental glacial ice that flowed eastward from the northern portions of the Puget ice lobe into the North Cascades. 

Lidar bare earth imagery of Lake Cavanaugh area

Blues arrows indicate ice flow direction with the arrow on the left being the main flow path of the Puget ice lobe and the blue arrow across the top indicating the ice flow from the Puget lobe up into the North Cascades. 

Lake Cavanaugh may have been an area of weaker fractured rock as it is aligned with the Darrington-Devils Mountain Fault zone.   

The south shore area of the lake consists or a series of alluvial fans associated with steep creek drainages coming off the north side of Frailey Mountain. Frailey Mountain is a steep ridge that rises about 2,000 feet above the lake. The bedrock on the mountain is mostly metamorphosed ocean floor basalts of the Eastern Melange Belt, a tectonic terrain. Sandstone and conglomerate of the Oligocene age Bolson Creek Formation underlies some of the mountain as well and there are areas of glacial sediment on the lower slopes.

Due to the steep slopes and narrow drainages the small creeks on Frailey Mounatin are subject to periodic debris flows.

Debris flow on one of the unnamed creeks in 2016.

There are some policy issues associated with these creeks but that will be another post. 

Lake Cavanaugh area was heavy logged in the past.  Bob and I came across this stump while heading up the slope to assess a potential debris flow source area.

The 1941 aerial image looks a lot like a lidar bare earth image. The clear cut logging throughout the area was very intense.   

  

1941

Note that there was a stand of trees left on some of the steeper upper slopes (but not the ridge line) in the 1941aerial. As the forest grew back the old trees are still evident in 1974 aerial. 

1974

They are not as apparent in the 2017 aerial, but logging in the area has started up again as the second growth is now merchantable and logging in the area has been intensive over the past 10 to 15 years. 

2017 - old tree stand circled in red

But the old trees remain. This remnant stand of old trees provides nesting habitat for marbled murrelet, an endangered sea bird that nests within old forest stands. A buffer around this habitat area is required for forest practices (proposed harvest). An added benefit is that bird's nesting presence and protection also reduces the potential for the very steep slopes from being damaged by tree harvest and has limited some of the recent proposed harvest on the north slope of Frailey Mountain.   

Cascade River Valley and Remembering Scott

I had a venture up the Cascade River in the North Cascades. The Cascade River is a tributary river to the Skagit River. The river was flowing hard through a bedrock section of the canyon from the parade of mild temperature storms that have passed through over the last week, but given the high altitude of much of the watershed it was not at flood levels. 

During my traverse I came across this boulder that had recently landed in a patch of sword fern and had a fresh chip on the surface of the rock.

Looking up the slope did not reveal much as to the source of the rock.

However, this area of the Cascade River is in a deep valley with steep valley walls rising 4,000 feet from the the river. My guess is the rock derived from a band of steep exposed boulder rich glacial sediments about 600 feet up the slope.

All in all I got very wet ploughing through ferns and brush in a forest of western hemlock, western red cedar and Douglas fir.

Heading out I was struck by the splash of yellow gold of a cottonwood amongst the evergreens.

The splash of color reminded me of a past fall trip up the Cascade River valley after a good summer of field work in and above the Cascade River valley.  I vividly remember the fall colors of that trip and always associate that trip with sadness and loss but also some joy. The brightness of those remembered colors as well as the bright cottonwood tree I saw on this day remind me of the brightness of Scott. I always associate him with the Cascade River valley in the fall even though he never saw it.

Mount Baker Steam before the Rain

 Before the latest weather front moved in I had a short notice/time critical job on Orcas Island. This time of year I can push back departure to the 7:30 AM boat instead of the 5:30 AM boat since it is still dark when the 5:30 boat arrives on Orcas. The ferry schedule has been tweaked a bit due to recent staff shortages related to COVID. 

Waiting at the dock I had a nice view of the early light and Mount Baker. With frosty temperatures and moist air a pretty good steam plume was emitting from Sherman Crater on the south side of the mountain. 

Mount Baker with Twin Sisters Range on the right