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ICYMI, Getting ready for the California Megastorm [1]

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Date: 2022-08-18

That was the last time - climate change is expected to make the next one far worse

I’ve written about this in the past here at Daily Kos, but darned if I can find the links. The prospect of a mega flood hitting California has been around for a bit. Scientific American had articles in 2013, here and here. [Thanks to JamieG from Md who tracked down my earlier diary.]

Tom Philpott had an extensive writeup in Mother Jones in August 26, 2020: The Biblical Flood That Will Drown California. It has a lot of historical data about the most recent flood in 1862 as well as estimates of the damage the next will do. The photos and maps are definitely worth a look.

The NY Times has put together an updated look (link below) at the potential for winter rains that come in over California as an atmospheric river, and don’t stop running. Think the equivalent of 26 Mississippi Rivers in the sky unloading over the golden state for several weeks. The climate models keep getting reviewed and revised.

The story now is preparations for the next one, and apparently the latest consensus is that it is overdue because climate change is going to make the next one more likely — and worse — because warming oceans put more water in the atmosphere.

The last time it happened was the winter of 1861-1862. The rain didn’t stop for 43 days. By the time it finally did, the Central Valley was a lake 300 miles long and up to 60 miles wide in places. The loss of life and property damage was immense. The NY Times reports the next flood is overdue. (The link below should allow full access.)

The Coming California Megastorm A different “Big One” is approaching. Climate change is hastening its arrival.

The article by Raymond Zhong with illustrations/graphics by Mira Rojanasakul and photos by Erin Schaff lays out an alarming scenario. It begins with a view of California showing the effects of rain as it comes in day after day. The scrolling text over the illustration gives the details as swirling waves of moisture sweep in from the Pacific.

..According to new research, it will very likely take shape one winter in the Pacific, near Hawaii. No one knows exactly when, but from the vast expanse of tropical air around the Equator, atmospheric currents will pluck out a long tendril of water vapor and funnel it toward the West Coast. This vapor plume will be enormous, hundreds of miles wide and more than 1,200 miles long, and seething with ferocious winds. It will be carrying so much water that if you converted it all to liquid, its flow would be about 26 times what the Mississippi River discharges into the Gulf of Mexico at any given moment. When this torpedo of moisture reaches California, it will crash into the mountains and be forced upward. This will cool its payload of vapor and kick off weeks and waves of rain and snow.

Millions of people will be affected by the storm; infrastructure will be overwhelmed by rain that could fall at the rate of two inches an hour. For those who have read “The Ministry for the Future” by Kim Stanley Robinson, Chapter 59 describes a scenario where the rains start and hit Los Angeles.

An article in Science Advances by Xingying Huang and Daniel L. Swain describes what is going on; here’s the abstract:

Despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods. Here, we investigate the physical characteristics of “plausible worst case scenario” extreme storm sequences capable of giving rise to “megaflood” conditions using a combination of climate model data and high-resolution weather modeling. Using the data from the Community Earth System Model Large Ensemble, we find that climate change has already doubled the likelihood of an event capable of producing catastrophic flooding, but larger future increases are likely due to continued warming. We further find that runoff in the future extreme storm scenario is 200 to 400% greater than historical values in the Sierra Nevada because of increased precipitation rates and decreased snow fraction. These findings have direct implications for flood and emergency management, as well as broader implications for hazard mitigation and climate adaptation activities.

This sentence from the introduction is of particular interest:

Recent estimates suggest that floods equal to or greater in magnitude to those in 1862 occur five to seven times per millennium [i.e., a 1.0 to 0.5% annual likelihood or 100- to 200-year recurrence interval (RI)] (5, 8).

emphasis added

In other words, a mega flood some time between now and 2062 would seem to be in the cards. The latest work of Huang and Swain has given California authorities new urgency in disaster planning for such a storm.

The New York Times article reports California has some big infrastructure worries. There are dams around the state that were never built to withstand the amount of rain a megastorm would drop. Levees and flood plain maps have to be reviewed in light of what could be coming. Evacuation routes, when and who to warn as events unfold, emergency shelter requirements… The problem is, while California may have been building for earthquakes, a megastorm wasn’t even considered as a possibility until recently.

All of this and more is being worked on. Huang and Swain have this to say about it:

Here, we describe the overall design and implementation of, as well as results from, “ARkStorm 2.0”—a new severe storm and flood scenario reimagined for the climate change era. Leveraging recent advances in atmospheric modeling by coupling a high-resolution weather model to a climate model large ensemble, we assess the meteorological characteristics of extreme storm sequences (henceforth referred to as “megastorm” events) as well as the subsequent extreme runoff and adverse hydrologic outcomes such meteorological conditions (henceforth, “megaflood” events) would produce under both present-day and warmer future climate regimes. This work builds upon previous research by explicitly considering long-duration (30-day) storm sequences (rather than single-storm events) most relevant to flood hazard management and disaster preparedness, characterizing large-scale ocean and atmosphere conditions associated with such severe storm sequences, and assessing the likelihood of these events over a wide range of potential levels of global warming. We find that climate change has already increased the risk of a GF1862-like megaflood scenario in California, but that future climate warming will likely bring about even sharper risk increases.

For what it’s worth, in the event of megastorm level atmospheric rivers starting to make their way towards the West Coast, it’s possible that forecasters might have up to a week to see what is coming in advance. That would give some time to get people prepared.

C-130J of the 53RD Hurricane Hunters

There is a way to monitor incoming rivers — the Air Force Reserve’s 53rd Weather Reconnaissance Squadron “Hurricane Hunters” at Keesler Air Force Base, Mississippi spend winter months doing flights out over the Pacific. Here’s their report from the start of the monitoring season, and a report from the conclusion of the flights.

From the final report for the season:

..Atmospheric Rivers are bands of moisture that come across the Pacific and, on average, carry as much as 25 times the water equivalent of the Mississippi River in the form of vapor. As a result, these systems account for up to half of the West Coast’s annual precipitation, and, subsequently, the flooding. The AR program is led by University of California San Diego’s Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography in San Diego who use the data collected by 53rd WRS and the National Oceanic and Atmospheric Administration Aircraft Operations Center’s Hurricane Hunters for forecasting and research purposes. “The purpose of our mission is to get over data sparse areas in the Pacific and collect data forecasters and researchers otherwise wouldn’t have in-depth access to,” said Capt. Garrett Black, 53rd WRS aerial reconnaissance weather officer.

The question is not if — it’s when. And what do we do afterwards?

Here’s an excerpt from “The Ministry for the Future” Chapter 59 from a survivor of Los Angeles after a mega flood.

“And what was occurring to me over and over again as all this was happening was, Hey: I hate LA. I was born here and I know it well, and have even read or been told some of its history in school, and I really do hate it. The truth is, after World War Two this place went from a sleepy little spread of villages to the ten million people here now, and during that time the developers were getting rich making ticky-tack suburban neighborhoods, that and putting in the freeways, which cut the plain into a hundred giant squares, and all of it crap. No plan, nothing good, no parks, no organization, no plan of any kind. Just buy some orange grove and subdivide it and tear out the trees and build a bunch of plywood houses, and then do it again, over and over. It happened in a snap of the fingers, and it was never anything but stupid. And that’s what we’ve been living in ever since! And more than a few of us trying to live out a remake of the movie La La Land. It was double stupid. So as we were paddling around in our kayaks, people were saying to each other, This whole fucking place is gone! Everything is going to have to be torn out! The entire city of Los Angeles is going to have to be replaced.

Which was great. Maybe we could do it right this time. And I myself am going to find a different job.” Excerpt From

The Ministry for the Future

Kim Stanley Robinson

https://books.apple.com/us/book/the-ministry-for-the-future/id1497486160

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