Flood Plain Hazards of Open Pit Mines

I missed the historic heatwave in the Pacific Northwest as I am currently in Germany. I am not in the zone that has been impacted and terrible floods, but the event is 'close to home' so to speak. Dave Petley (HERE) noted a river in the west of Germany that broke out of its course and flowed into an open pit coal mine in Inden. 

Dave noted the river course into the mine followed an old channel. That channel was the former river channel up until about 15 years ago. The channel was blocked and the river was rerouted in a long circuitous route around the mine.

Blue line shows river route around open pit coal mine

Blue line showing most recent river route and red line showing former path

Although the flooding of the coal mine was impressive, a more dangerous flood into an open pit mine took place a few miles away at Blessem. NPR led their story on the flooding with an image that had a caption about an entire field collapsing due to flooding (npr.org/germany-belgium-flooding). 

  (picture alliance/dpa/Rhein-Erft-Kreis | Rhein-Erft-Kreis) The image shows very rapid headward erosion as floodwaters drain off the flood plain down a steep gradient. The source of that gradient was and open pit sand and gravel mine. 

Same site looking toward the mine  (picture alliance/dpa/Rhein-Erft-Kreis | Rhein-Erft-Kreis)

Red line is approximate extent of area eroded. The yellow line is my measurement of the headward erosion distance of 850 feet.

The headward erosion continued after the above image and expanded into the town taking out a number of buildings. 

 

In this case it appears that flood waters on the flood plain began to flow rapidly towards the pit as the water drained towards the low area of the sand and gravel mine. While gentle slope wide flood plains have flood risk and potential hazards associated with channel movement. The rapid erosion associated with flood water flows into open pit mines is well demonstrated at this site.    

Notes on Heatwave Global Warming Attribution

Phillips and others (2021) have taken a rapid assessment run at global warming attribution of the 2021 Pacific Northwest heat event. A summary of key points is provided at the beginning of the paper. Two points stand out:

The observed temperatures were so extreme that they lie far outside the range of historically observed temperatures. This makes it hard to quantify with confidence how rare the event was. In the most realistic statistical analysis the event is estimated to be about a 1 in 1000 year event in today’s climate.

This simply emphasizes what most long-term Pacific Northwest residences felt - this event was very far from what anyone expects for northwest summers. For those that experienced the event, you have a story to tell. But this was more than a remarkable event for the Pacific Northwest; Christopher Burt author of Extreme Weather stated “This is the most anomalous regional extreme heat event to occur anywhere on Earth since temperature records began. Nothing can compare.”   So for those that went through the event (I missed it), you can say you went through a world historic weather event.

There are two possible sources of this extreme jump in peak temperatures. The first is that this is a very low probability event, even in the current climate which already includes about 1.2°C of global warming -- the statistical equivalent of really bad luck, albeit aggravated by climate change. The second option is that nonlinear interactions in the climate have substantially increased the probability of such extreme heat, much beyond the gradual increase in heat extremes that has been observed up to now. We need to investigate the second possibility further, although we note the climate models do not show it. All numbers below assume that the heatwave was a very low probability event that was not caused by new nonlinearities. 

Under the first possible source, that the event was a very low probability event, global warming additive attribution pushes the temperature upward some amount more. Phillips and others (2021) note that the observed annual maximum daily temperatures in the Pacific Northwest trend is approximately 2 times the global temperature trend. So regardless of the event being rare, our heatwave temperatures have been trending upward at a greater rate than the global temperature trend as well as our local temperature trend.

Figure 4 b) Annual maximum of the index series with a 10-yr running mean (green line)

Burt noted in 2017 that Seattle has had 122 record high temperatures since 2010 compared to 19 record low temperatures and Salem has had 98 record highs compared to only 11 record lows.  

Another potential added source of heat is the trend of 500hPa height associated with a warming expanding atmosphere (Christidis and Stott ,2015). 

Phillips and others (2021) also suggest a source of added heat may be from persistent drought in the west leading to higher temperatures.

Given the circulation associated with major heatwaves in the Pacific Northwest, drought and enhanced heating in the southwest will be a contributing factor as hot air from that region descends into the lower elevation areas of eastern Washington and across the Cascades to the west side. 

Phillips and others (2021) suggest that global warming pushed the temperatures about 2°C warmer than they otherwise would have been. 

The other question or cause would be the potential that the heatwave was caused by a 'nonlinear' factor related to global warming. Phillips and others (2021) do not attribute this event to a nonlinear event such as a wavy stalled jet stream, but do give it a brief discussion and suggest further analysis. 'Stuck' jet streams or omega blocks are a point of some debate in climate science. 

I would note that this attribution paper was a bit narrow. John Pollack (HERE) notes that this event was preceded by two western US heatwaves of similar pattern, but to the south in June that set records including tying the all time high temperature in Palm Springs, CA of 123 F. Those events likely provided some additional heat charge to the third high pressure event centered in south British Columbia with southeast flow of air coming up from the southwest U.S into the Pacific Northwest. And the pattern of high pressure heatwaves of long duration is continuing. From the National Weather Service: The current forecast for Las Vegas is just below the all-time record of 117.  This is the fourth western US major/record breaking heatwave in the past month.

A Few Notes and Readings on the Heat Wave

I missed the heat event in Washington as I am out of the area. So I have no direct observations about the event. From afar it was really remarkable to follow this event as it developed. The weather models and projections were alarming and I will say it caused a level of concern for friends and family. I will also add that I have spent a fair bit of time in the Fraser River canyon and it is is painful to think about what has happened in Lytton.    

First of all, the weather prediction models were amazing. Models can be useful, but it really is remarkable when the models indicate something that has never happened and is an extremely rare event and the actual event happens as the models indicated.  

Phillippe Papin via twitter.com/pppapin/ lays out the antecedent event in the tropics and how the extreme heat would be generated. Note the post was June 23.  

There were a few statements made during the run up to and after the event that warrant repeating:

From the National Weather Service Seattle Office as the heat event was about to take place:  "As there is no previous occurrence of the event we're experiencing in the local climatological record, it is somewhat disconcerting to have no analogy to work with." --- National Weather Service, Seattle on June 27, 2021. 

This statement from Bob Henson and Jeff Masters clarifies what a big deal this heat event is: "Never in the century-plus history of world weather observation have so many all-time heat records fallen by such a large margin than in the past week’s historic heat wave in western North America. The only heat wave that compares is the great Dust Bowl heat wave of July 1936 in the U.S. Midwest and south-central Canada. But even that cannot compare to what happened in the Northwest U.S. and western Canada over the past week.", Bob Henson and Jeff Masters (worlds-most-extreme-heat-wave-in-modern-history)

Jeff Beradelli (Here) -- "To put climate extremes into perspective we measure against the average. The sigma is the standard deviation of a normal distribution of expected values. In this case the heat dome sigma max is 4.4 - that means it's outside of 99.99% of expected values or a 1/10,000+ chance.

 Bumbaco, Dello and Bond (2013) describe of how most heat waves develop in the Pacific Northwest and that description is consistent with this latest event. They note "Current research suggests that the frequency and duration of heat waves are expected to increase in much of the United States, and analysis of the heat events reveals that a significant, increasing trend in the frequency of the nighttime events is already occurring in the Pacific Northwest. A heat wave occurred in 2009 that set all-time-record maximum temperatures in many locations and ranked as the second strongest daytime event and the longest nighttime event in the record."

This chart shows that since the 2013 above described paper there have been a number of additional heat evets of 20+ above normal, and this event blew way past what took place in 2009.  

The attribution of this event to anthropogenic global warming (AGW) will be analyzed in detail. The attribution of AGW to extreme heat waves has been generally strong (Special Supplement to the Bulletin of the American Meteorological Society Vol. 102, No. 1, January 2021).