California megafloods! New research, articles, prepping challenges, etc.

pnwsarahContributor - August 12, 2022

Scenarios

I don’t think we’ve had a forum thread on this before… LMK if I’m wrong and I’ll delete this and move my links and comments to the appropriate place, but the WaPo ran an article on megaflood risk in CA today.

If you get paywalled, here is:

• The research article that prompted the press coverage (which is allegedly open access)
• A long Mother Jones feature from a couple of years on the same subject

TL;DR — California can get enormous rainfall events that generate enormous floods. There was one in 1862 and it basically turned the Central Valley into an inland sea and drowned a whole bunch of cattle. It would have been a bigger deal if the area were settled and farmed the way it is now. It will happen again and cause all kinds of havoc, destruction, loss of life, etc. My husband called it, “California’s Cascadia Subduction Zone earthquake.”

The thing that makes this so hard to grok for me is that, unlike likely shaking intensity for earthquakes, tsunami run-up, ordinary FEMA flood risk, and event wildfire hazard, this scenario doesn’t seem to have been modeled at the local scale. There isn’t a GIS where I can plug in my address and see whether it will be underwater or not, or plan an evacuation route.

My husband said, “We’d have five days notice, so, have sandbags ready to deploy, move everything valuable to the second floor, and evacuate.” Having sandbags and sandbag alternatives on hand seems like a no-brainer, and a list of things to move to the second floor or take (in addition to BOBs) is easy/consistent with work I’ve already done, but “we’d have five days notice… just evacuate” seems like a bad strategy given the tendency among Bay Area weather media people to totally overhype winter storms, especially those involving atmospheric rivers. If feel like all it would take is a good El Niño year and we’d be evacuating every week. Also, I have no idea where we’d go: “Head for the hills” doesn’t seem like a great rule of thumb given the propensity of the Coast Ranges to rearrange themselves under the duress of a wet winter.

Anyone else thinking about this?

(Edited to address formatting issues!)

50  

pnwsarah,

What do you mean by this ‘… just evacuate” seems like a bad strategy given the tendency among Bay Area weather media people to totally overhype winter storms, especially those involving atmospheric rivers.?

What is the media doing?

 

I haven’t lived in CA in a few years, so my memory is pretty fuzzy, but in the ’10s, some winter storms generated huge buzz— enough that memes were made mocking the disconnect between the rhetoric and the reality. It wasn’t so much a one-off mistake as a pattern of storms that were smaller than everyone had seemed to expect based on the advance reporting. I think it was the convergence of 24-hour weather news culture sort of spilling over into mainstream weather reporting (i.e., weather reports becoming entertainment), the rise of the term “atmospheric river”, and— maybe most importantly— the fact that we were in a huge drought and perhaps everyone (media, local gov, regular folks) was kind of eager for some giant deluge that might signal the end of it.

Basically, my observation is that when I lived in CA, there was one way that media and local government behaved when a big, wet storm was coming— regardless of whether it was just the biggest one we’d had in a while (but not very big, strictly speaking) or something with much more potential to cause harm. It’s not like there is a numeric rating system for storm severity like there is for hurricanes. I don’t necessarily think that we need one… but I do wonder how clear it’s going to be when a Really Big storm comes, given that ANY storm kinda gets treated like a major event. 

Does that clarify what I meant?

 

The Mother Jones article is well written and ominous. A very good reason to grow our own vegetables.

 

As a local SoCal transplant from Ohio, I can totally agree with this assessment. When I first moved here, I told my mother that any weather event is such a big deal they name it – El Niño storms, Santa Ana winds, etc. I since learned that there are conditions that define these names, but the reporting can get overly dramatized. When what would be normal rain in other locations is called “Storm Watch pick a year”, it’s desensitizing the public to truly significant events. A very good example is a 405 freeway closure named Carmageddon. The way it was communicated, it sounded like it would be for a significant duration – like months or year: Doctors relocating; Flights between Burbank and LAX. It was a weekend – 42 hours in actuality. Perhaps it was a CYA activity because this was a public works closure versus a natural closure like the freeway collapses during the Northridge Earthquake.  

I also agree that it’s gotten worse with the internet/social media influence of soundbites and headlines.  TL;DR means that everything must be short and sensational to garner any attention. 

 

Alicia, thank you for explaining the kind of thing I was referring to with MUCH more specificity! That’s it exactly!

 

I used to live in San Diego, near Otay Lake.  You could walk across the dam and see the footings and ripped steel of the previous dam.  The previous dam was destroyed by a flood.  The blame for the flood was placed at the feet of a rainmaker, who coincidentally or not, was in the wrong place at the wrong time when Mother Nature decided to unleash the flood.

If you read the book Seabiscuit, you will read the story of the humongus mountain of manure that was washed out to sea from the Caliente racetrack just south of San Diego in Tijuana.

I remember riding my horse through dry river beds that were restored to living rivers in Bonita. 

California is occasionally visited by disastrous rains.  It’s happened before, it will happen again.  Knowing this, prepare accordingly.

Barb Lee, formerly posting as Dogpatch

 

One thing I’ll add now that I have a minute: I think the way to know when to evacuate is to read the research article more carefully than I have thus far and understand the specific type/position of low pressure system that would give rise to this scenario, and then figure out what resources report on those variables. In grad school I had a professor who used to send out these extensive, very formal/scientific, all caps weather alerts from the National Weather Service to the entire department via email whenever there was a significant weather event on the horizon… I bet that resource would provide enough jargon and detail to match with criteria pulled from the research article (though I def. do not want to get those alerts in my inbox every day).

 

Accurately predicting major weather events is a full-time job. So unless you’re thinking of changing careers, probably better to search for a more reliable weather service. And no, I haven’t found one yet. 😅

 

Hmm, not sure what you mean exactly, Eric— maybe you’re misunderstanding my comment? The problem is that local media treats every impending atmospheric river as a major event, so you can’t use the words “atmospheric river” + the level of alarm shown by media or local government as an indicator of how serious the storm will be— if you did that, you’d be evacuating constantly. However, the research article suggests some additional meteorological factors that are associated with the megaflood scenario, and there are sources that do report in that level of technical detail, so the idea is to couple a more detailed set of factors that signal a megastorm with a more technical forecasting source. I don’t think that will require returning to university.

 

“the idea is to couple a more detailed set of factors that signal a megastorm with a more technical forecasting source”

When you’ve figured out the process I’d be interested in hearing more about your approach.

Without having done anything like this myself, it sounds hard. And it sounds like something that an expert is already doing – if we just knew the right person or agency to listen to.

 

Okay, gotcha. I will look at the article and try to find that thing my old professor sent around and report back. (I wish I could remember where it came from— it was very government-y and jargon-heavy. Like, it was for fisherman, boaters, scientists, and NERDS.) It does sound hard but I think it is doable— in part because the ARkSTORM people clearly have good media relations and relationships with scientists who care about communicating risk to the public. I think the WaPo article hints at some key things to look for and reading the “Intro” and “Discussion” sections of the paper might be enough to get a working list going. 

 

@pnwsarah, thank you so much for finding this and also noting it in the current events discussions. I didn’t remember ever learning about California megafloods and everything you linked has been an engaged and unsettling read. (Even as someone who never plans to live in Californa, the impact of a flood on the rest of the country is still looming, and I’m spending time reading about this risk due to those impacts.)

Did you ever end up spending more time on this paper (in the last half a year)?

I’m reading/skimming Huang and Swain (HS2022) now. I am not a meteorologist, but I liked your idea for trying to pull useful features from HS2022. However, after reading, I think the article alone won’t provide the information an individual household needs to make good evacuation decisions faster than those 5-7 day out weather reports you already mentioned.

I’ll suggest that California preppers might get better mileage finding a meteorologist who is interested in the paper and interested in tracking practitioner/research updates for how to predict such a storm (eg. someone else to talk to other meteorologists and also track/read/translate subsequent papers for non-weather-pros). I think finding such a person (or people) and subscribing to their updates(/getting on their phone tree) for a warning when conditions look sketchy, could be a more helpful alert than preppers trying to search NWS detailed forecasts themselves for these features. (Unless someone out there already wants to learn to understand these features enough to become a hobby/pro meteorologist, in which case, please post your social media updates here when conditions look sketchy!)

My comment is super long, but here are my notes from reading the parts of the paper I thought relevant about what conditions could lead to such a really big storm.

In the introduction, the authors state “This work builds upon previous research by…characterizing large-scale ocean and atmosphere conditions associated with such severe storm sequences,” which gave me hope initially, since that communicates their intent to give information that could lead to predictors of a megaflood. (I say could lead because they rightfully say “conditions associated with” rather than “conditions causing”.) The immediate next section, “Large-scale and regional climate conditions associated with megaflood scenarios,” dives into these associated factors that could one day lead to credible predictors of a megastorm event.

For their modeling, they created regional weather simulations from two sets of climate data: (1) historical* climate data from 1996-2005, labeled “ARkHist”, and (2) simulated climate data for 2071-2080 from another model that assumes a “high [global] warming” scenario, labeled “ARkFuture”.

* (I’m 90% certain it’s actual, highly detailed historical data and not instead a highly-detailed model that does the best-in-class job predicting less-detailed actual historical data and thus is used by scientists to fill in the details, but that 10% uncertainty means I might re-read the methods section more closely later.)

For each of these two regional weather simulations, they checked each 30-day period possible and looked for the three 30-day periods that weren’t right next to each other and that had the highest total (cumulative) precipitation. The authors picked one out of the three periods to focus on when discussing the conditions and impacts of the storms and when comparing the historical data to the high warming future data. (They picked which one out of the three 30-day periods in a subjective but still practical manner: they assessed which of those top three storms would be difficult for emergency managers across the whole state of California to handle.) For just the two chosen storms, they discuss the following features:

• Both occurring in El Nino years (“warm-phase ENSO”)
• “maximum SST anomalies located in the tropical central Pacific … consistent with so-called “central Pacific” or “Modoki” El Niño “
• “Warm (positive) SST anomalies are also present in the western Bering Sea and Sea of Okhotsk, as well as along the immediate California coast, in both cases.”
• “a broad region of negative sea level pressure (SLP) anomalies is centered over the Gulf of Alaska and adjacent portions of western North America—consistent with traditional El Niño teleconnections—although the zone of negative SLP anomalies extends farther westward across the North Pacific in ARkHist.”

However, then they do good scientific diligence and go on to say “We acknowledge, however, that these large-scale patterns and associations with ENSO are drawn from only two individual scenario instances, and we cannot determine from this analysis alone whether these relationships are robust across a wider range of potential megastorm events.” (Emphasis added by me.) Basically the list above can’t effectively be treated as credible predictive features of an incoming megastorm. It’s super tempting, but that’s really just a start. And maybe future research will end up supporting a few of these features as credible predictors. But maybe future research will end up casting doubt and identifying much better predictors not mentioned here. From this part of the paper, there’s not nearly enough information to go on for predicting the when of a megastorm/megaflood. Which is not really a surprise, because I think the major goal of this paper was to create a plausible scenario for emergency managers use in exercises (and also check “is it worse with a warmer global temperature?”).

Given they acknowledge this limitation to these initial features discussed, the authors introduce an additional analysis that goes back and grabs the top 4 thirty-day periods of greatest precipitation from both simulations (top 4 for ARkHist and top 4 for ARkFuture), once again simulates the super detailed weather models for these periods and then discusses the following features after looking at all 8 thirty-day periods of highest precipitation:

• “anomalously warm conditions in the tropical Pacific Ocean”
• “Niño 3.4 SST anomalies are uniformly positive”
• They also check a better quality measurement of ENSO Longitude Index (ELI) (“an ENSO metric that tracks the average longitudinal position of ENSO-associated deep convection”).
• The ELI suggests these storms have less in common than the Niño 3.4 SST anomalies might imply (“ELI values more clearly illustrate a wider range of ENSO spatial variability and dynamical intensity”).
• The ELI measures can be categorized as either “strong El Niño” (4 of the events), “moderate El Niño” (3 of the events), and a “nominally” moderate El Niño (the last of the events).

At this point, they’re comfortable enough to say some magic words (“these findings suggest”), but the discussion is again about features of those eight 30-day periods identified in their simulations: “These findings strongly suggest that there is a substantially elevated likelihood of month-long storm sequences capable of producing very large precipitation accumulations during moderate to strong El Niño conditions and that the conspicuous anomalous deepening of the Gulf of Alaska low present in most of these eight events (fig. S3) is plausibly linked to El Niño teleconnections.”

The following two paragraphs then discusses a whole host of other metrics and patterns observed. The first following paragraph introduces the integrated water vapor transport (IVT) metric, then discusses a “primary storm mode” of atmospheric rivers, things like “a well-defined moisture transport axis extending northeastward from just north of the Hawaiian Islands to central California,” and atmospheric river families. The second following paragraph discusses “composite atmospheric instability,” including levels and spatial distributions of “convective available potential energy (CAPE).”

Then the section on these characteristics ends and I am left with the strong impression that this is a list of features that will be great for future researchers to look into, but not helpful for households trying to set credible alarms for brewing CA megastorms and megafloods. (Especially if someone wants to evacuate for a 30-day megaflood, but to stick around for a two-week parade of atmospheric rivers, and needs predictive features that will distinguish between the two.)

The final kicker reason I think this paper can’t help laypeople predict a megastorm+megaflood event shows up in the more detailed “Materials and Methods” section at the end. The two underlying periods (1996-2005 historical and high warming future) were chosen because they were pretty much the only two currently available with detailed enough data to run the cool weather simulation model used here.

So this paper did a nice job with its goal of “if we simulate plausible weather with cutting edge models and study a megastorm that formed in the simulation, here’s what that storm actually looks like, and let’s give this to emergency managers for the ARkStorm 2.0 efforts.” But this paper hasn’t really made notable progress on the question of: what are all the various weather conditions that could give rise to a megastorm that generates a megaflood, and which conditions are the best/better predictors of such a storm? (Which is the question we’d like to have answered for getting a heads up on danger looming.)

Ok, now it’s time for me to get off the stage here. 🙂

 

Oh wow, thank you internet and awkward timing — I just found a link to the website of one of the authors, Dr. Daniel Swain: https://weatherwest.com/

 

I can’t weigh in on weatherwest.com — but I follow the author (Daniel Swain) on Mastodon and he’s been a great source of data the last couple weeks. (When he posted a few days ago that this wasn’t looking to shape into an arkstorm scenario, I was relieved, and when he posted yesterday about a returning west coast ridge shaping up on the models, I was again relieved.) If anyone else follows anyone that they think is providing good info on this topic, please share as I’d like to add them to my feed as I find this information more helpful than the big news websites.

 

Did you ever end up spending more time on this paper (in the last half a year)?

No, and now I don’t have to, because you just did it— THANK YOU for saving me the trouble! (I am not a modeler and I really do not enjoy reading modeling papers, both because I have to work so hard to understand them and because that engenders some regret about how I approached building my methods toolkit in graduate school.) The candidate factors you distilled match my memory of the language in the paper that made me think we could pull “factors” from it; part of what I had intended to do was pull out more “factors” (which you’ve done here); the other part was to re-read the language around those “factors” to see how much the paper even supports their use as such. The tricky thing, of course, is that at this stage of the endeavor, we’re not going to get anything better than a “these findings suggest”, so a deep dive into the methods is really necessary to figure out how strong the suggestion is. I did…. not want to do that at all, and now you have done it, so, excellent!

If I seem very happy about the fact that my original plan for figuring out when to evacuate is now voided, that’s because I got to the same place just by living through these past couples of weeks in California and reading the news and watching CalTrans road closures and local evacuation orders. This series of storms has demonstrated that even if Huang and Swain had identified a set of factors that they were comfortable characterizing as strongly predictive of an ARkStorm-caliber event, it would still be really tough to evacuate on time: Roads are going to be trashed here long before it’s clear that we’re facing a megaflood-producing storm series. I recently read somewhere (I thought it was Swain’s blog, but I can’t find it there now) that we’ve had maybe 1/3 of the precip that an ARkStorm would produce, and it has been two weeks, compared to the month of ARs in the ARkStorm scenario. What we’ve had has been more than enough for landslides and downed trees everywhere. We’ve had exactly one clear day this year that was forecast as such. This may not be true for folks in the Central Valley, but for those of us in the 1 and 101 corridors (closer to the coast), I can’t see driving around in the Coast Ranges to evacuate as a particularly good idea.

I feel kind of dumb for not having thought of this earlier: I have lived in NorCal most of my life, and I know how things tend to go to pieces when it rains hard after a drought, but I’ve been out of state for the last three years, and the way these storms have come in on top of each other is pretty rare… 

So my current evac strategy is “hope for a couple of decades’ worth of research advances before I need to have one.” For our household personally, that isn’t totally unworkable: These storms have demonstrated that our neighborhood is extremely unlikely to flood, so preparing becomes a matter of keeping a lot of food and water around, which is something we do anyway. For those in low-lying areas, though? I don’t know.

Again, my sincere thanks to you for doing an incredible job on a task I had been putting off!

 

Slow reply on my part, but glad to help, and thank you for leading me to the paper in the first place!

 

That was an interesting article in Mother Jones. Living in the Central Valley with than expected. a father that worked on the “water” business for 36 years gave me a multifaceted view of water issues. I’ve heard stories of the 1969 winter with 300″ of snow in parts of the Sierra. Then to see in come downhill sooner and with greater volume and overfill our dams and river channels was eye-opening. I got to see the Tulare Lake Basin fill again, only later realizing how much farmland was inundated and put out of production. I can believe it will happen again and with a population less prepared.

As a side note there are stories of paddle wheel steamers that provided transportation services from Bakersfield and Fresno to San Francisco, so high water wasn’t abnormal. In the wet year of 1981 a gentleman paddled a kayak from Fresno to San Francisco. some of the trip was upstream in newer channels and the kayak aided in portaging around irrigation headgates.

 

I live in the Sacramento Valley and have given it a fair amount of thought.  I think the original ARKStorm 1.0 study did have inundation maps, but the published maps were too low-res to see where we live in detail.  You might be able to get the data but I wouldn’t be savvy enough to make use of it if I could find it.  Generally, our house is about 100′ above the Sac River elevation at the same latitude.  I think it’s reasonable to expect we’ll be above water.  Whether we’d be able to get groceries or have functioning public utilities would be another issue.  I work in healthcare and would have a hard time leaving town in the midst of a regional disaster, but I would try to get my family and our camper over the mountains to Reno or somewhere.  I think the best prep is getting FEMA flood insurance.  The up-side of FEMA flood maps underestimating risk is that the insurance is pretty cheap unless you live in a swamp or immediate flood plain.  The ARKStorm 2.0 article you referenced said they were going to do more work including inundation mapping, but I think you can learn a lot by studying local topography and seeing what happens with more ‘typical’ atmospheric river storms.

I wouldn’t trust the weather media either.  When your weather is really boring 300+ days/year, anything out of the ordinary is given the same crisis-level attention.  I think flood risk here comes in 3 varieties.  One would be local weather events which are hard to predict (inches of rain in a few hours with localized flooding).  Levee and dam failures are also unpredictable (Marysville flood in mid 90’s, Olivehurst in mid80’s, Oroville dam near-failure 2017).  Bigger flooding events should give some warning.  You can watch the snowpack levels, river/reservoir levels (water.usgs.gov) and rain accumulation forecasts (I use the Windy app).  Big snowpack, full rivers and lakes with an impending warm rainstorm in late Winter/early Spring means you should be on the lookout.  

CA is tricky — too low and you risk flood.  Too high and you will burn.  There are some areas that seem to balance the risk of both but it’s a narrow band.  Definitely look into FEMA flood insurance.

 

Fantastic advice— thank you! Leave it to someone from the Sac Valley to have done their homework on this scenario. This is a little embarrassing, but I actually thought you couldn’t get FEMA flood insurance unless you were in an area that FEMA mapped as high-risk. If we could get cheap flood insurance, that would give us a lot of peace of mind.

I also like your description of the “narrow band” that minimizes exposure to both flood and fire. That was definitely how I was thinking when we bought our house, and I think we threaded the needle pretty well— we’re neither up in the hills nor particularly low-lying. However, the neighborhood drains poorly and the house is on a slab. I wouldn’t be very concerned about flooding if it weren’t for that. I don’t think we’d be ten feet deep in a megaflood— I don’t even think we’d get three feet in that scenario— but 4-5 inches? Sure. And that would be enough to cause a serious, costly mess.

Sounds like you did it right, too, if you’re in the valley but 100′ above Sac River elevation. That sounds promising. I was struck by maps in the Mother Jones article that show how quickly you get out of the danger zone just going east from Sac— Rancho Cordova and Carmichael look just fine.

Will check out your app rec and the USGS site. The plain-language description of factors to look out for probably saved me having to read the whole paper, too, so extra thank you!

 

Thanks pnwsarah & AT! I’m not far from you, and for about 10 years did carry flood insurance because although we live on a slight rise, we’ve seen flooding just a mile south of us & have a slab house also. At the time it was only in the $400 range for a year of flood insurance. We eventually let it lapse after close observation of water events, but you got me thinking & doing more research! Last year’s “atmospheric river” dumped some 5 inches in 24 hours, but we fared fine here at about 35’ elevation. I did stock a box of 100 sandbags just in case…very cheap insurance indeed although filling them when urgently needed may be a problem. I think you can also get a water fillable tube that functions the same, but have doubts about its efficacy. 

 

We are much lower and still fared well because we have sandy soil that just absorbs the rain.  In 20 years we’ve never even had a puddle in our yard.  But those maps show basically Sac, West Sac, Stockton, Fresno, LA, etc., under a considerable amount of water (I wish it showed depths).  I understand the next paper to come out will have more detailed modeling, but I don’t know the timeline. 

 

“the neighborhood drains poorly”

The best prep for this may be a neighborhood project to improve drainage and prevent flooding.

My HOA recently finished a drainage improvement project that included cleaning out the drainage pipes and clearing some brush/debris from around one of the pipes.

”the house is on a slab”

I’m probably missing something obvious here, but… why does your house being on a slab change your flood risk?

 

“The best prep for this may be a neighborhood project to improve drainage and prevent flooding.” 

Great idea if you have an HOA and can sell them or local government on this. We’re not in an HOA, but we have thought about contacting the county and asking them about drainage in the area and whether there are any plans to improve it. They recently put in a park nearby with an incredibly intense drainage system, which actually made us even more nervous, since it was so far beyond what we would have thought necessary. It made us wonder what scenario they were planning for.

“the house is on a slab” — I meant that literally, not that it has a slab foundation. There is no basement or crawlspace. 

 

In our case Eric, the slab foundation, while being nice & stable temperature & minor earth movement wise, puts us only about 6” above the level of our yard & pasture in a larger area that’s mostly pancake flat with a slight rise here & there. So, any floods here over 6” will come right in, and 3-4” feels really close. Raised foundations have their own flood issues: while the flood generally has to be higher before it enters the house living space, the movement of water under your house could move or destabilize the load bearing piers which could create larger issues that are even harder to repair. Our house would get really gross, but probably not move/shift as there’s nowhere any significant current would come from. Previous floods in the area show it just creeps up, then slowly subsides. We’re in a country area, so drainage consists of our neighbors having ditches, with typical variability on how well they keep them cleaned out. 😉

 

AT, nice post!

“…Whether we’d be able to get groceries or have functioning public utilities would be another issue.  I work in healthcare and would have a hard time leaving town in the midst of a regional disaster, but I would try to get my family and our camper over the mountains to Reno or somewhere…”

The nature of a disaster as described in the study would mean infrastructure, power and supply are smashed for a long time. The human misery would be hard to imagine. Getting out of Dodge at the first sign of danger would be prudent. It might even be a good idea to store a few top-lock 55 drums with spare clothes and shoes/boots in a tiny storage rental in Reno in the meantime.

“…I work in healthcare and would have a hard time leaving town in the midst of a regional disaster…”

This really hit home for me. I respect you greatly for this.

Healthcare devotion to patients, team, duty and mission is a hallmark of the industry in this country. COVID19 saw turnover rise in healthcare and that’s not unexpected, after all, healthcare is a reflection of society. I have seen so many small acts of heroism, duty and empathy among healthcare workers that it has left deep impression on me.

I have recently left my job working in a military hospital after many years. I am not a soldier, a veteran or clinical. I was a civilian in a leadership position in IT (or IMD, as the military calls it).

I believe there would be an overwhelming response to a disaster in the Central Valley from all over this country. It would focus the nation on the best of Americans and our love of country.

That being said, after the initial response, some very hard decisions would have to be made by many people in that area.

Right after Katrina I read an excellent blog by a young man and his escaping the storm with his wife. They went to her aunt and uncles’ home in Houston. What was notable was his discussion of their decision to start over in Houston after they realized the full extent of the damage in New Orleans and the lack of jobs.

He spoke about putting together all your stuff to start over again professionally. Documentation of licenses, certifications, and training to get a similar job in your new home.

https://tinyurl.com/53umcna5

 

Great topic!

Here are two more related forum posts about flooding, but this topic here is definitely it’s own thing and am glad it was created.

• Flood Barriers: alternatives to sandbags
• Flood preps & emergency raft recommendations

 

Thanks, Gideon. There is TONS of good info. in the first thread— I’m sure the second one, too, just haven’t gotten there yet. But I will… we’re moving back to CA in the fall and I will probably tackle it then. I guess I’ll enjoy a couple more blissful months with only the CSZ earthquake to worry about. 😀

 

pnwsarah, you have read the second thread – you have posts in it.  🙂 

Thanks for the links Gideon.  The Aquadam mentioned in the first link may be a good option for a flooding event to store water for those in the upper elevations who, as AT put so well, are cut off from access to groceries or no longer have functioning public utilities.   An ARkStorm event would by its definition last 30days getting worse and worse as the days pass.  Any rain barrels would be overflowing, but this could be connected and filled as a natural collection of fairly uncontaminated water.  It would need purification to consume but wouldn’t be the cesspool that the flood waters would be. 

 

Ha, so I did! I just didn’t remember from the link that that was the one where we had the Rapid Raft conversation.

On the bright side… that raft will still be useful (at least for peace of mind purposes) when we move back to CA.

 

“There isn’t a GIS where I can plug in my address and see whether it will be underwater or not, or plan an evacuation route.”

Try plugging your address into this site to see your risk of flood or fire (in percentage) for this year and for the next 30 years. You can also plug in just your zip code to see how risk varies within your area, which is a helpful starting point for planning evacuation routes.

https://riskfactor.com

 

We’ve used this site before, and it looked then (and appears now) like the high res maps aren’t available yet (and will be for paid subscribers only), at least in our area— were you able to find them for your area? The closest I can get is super zoomed out (e.g., the whole SF Bay Area).

I’m also not sure the data incorporates the possibility of an ARkSTORM-style event, which itself is a conservative estimate (since they had to simulate the event by basically combining a past NorCal and past SoCal storm, which is not really the same or as big as what happened in 1862). The discussion of the First Street Foundation Flood Model here implies that they do make efforts to take historic events for which there aren’t good data into account, but it’s hard to know if they did that for any one historic event in any one location. (The technical report provides more info., on p. 45, but I think I would have to go back to school to really understand all that.)

My assumption here is that this is all going to shake out the way the Cascadia Subduction Zone earthquake tsunami modeling did— they needed a few iterations of modeling after the threat was identified to get really good information out there in formats that the public could actually use— and we’re just too close to the “threat identification” point to have those tools.

I’m glad things like this are starting to crop up, though, and I wouldn’t discourage anyone from using a site like this, I just suspect it underestimates flood risk, at least in CA. If you or anyone else can tell otherwise, it would be great to hear further thoughts.

 

“We’ve used this site before, and it looked then (and appears now) like the high res maps aren’t available yet (and will be for paid subscribers only)”

I know this was available before because I used it in that manner. Going back now I can no longer find it. Probably they’re trying to make the pro version more appealing.

 I still recommend this site for getting risk estimates for a specific address, but it seems that risk maps are no longer available.

 

Ah, bummer. I agree, though, still useful. I feel like it would be most helpful to me if I were moving to a completely new area of the country where I didn’t know the history of floods and fires. It gives you a place to start understanding risk (before you buy a house or sign a lease). But if you know generally where the fire and water would come from and where they would move to… it’s all about getting those dang maps! I really like your idea about using the map view to chart an evacuation route, as well. Even if it underestimates flood risk, a map would still tell you which areas are going to be underwater first.

 

“Even if it underestimates flood risk, a map would still tell you which areas are going to be underwater first.”

Exactly. In my case, I determined that my flood risk was very low and was more concerned about fire. I assume that any large fire will start in one of the highest risk parts of my zip code (which riskfactor conveniently showed me on a map), so my evacuation routes need to avoid those areas.

There is a forest just north of me that I can’t avoid in an evacuation. My HOA/neighborhood entrance is across the street from that forest. Riskfactor indicates that highest wildfire risk is NW of me, so my plan is to travel east along the forest for half a mile then take the first available turn to the south. After that, the wildfire risk drops to near zero, and I can just head into the much lower risk city center to wait it out.

Flooding is somewhat simpler. We can all be certain that large scale flooding will start in the lowest areas, or at least areas that are lower than their surroundings. So you could try using a topographic map to help with planning evacuation routes.

 

Realtor.com shows pretty detailed flood and wildfire risk for most areas of CA.  The data comes from RiskFactor.  There is some consideration of climate change, but probably not the ARK STORM data.  I find it pretty useful though.

 

This is only my second time posting here.  This scenario worries me a lot.  We’re in a drought, so I don’t think this risk really registers with a lot of people, but the record-breaking 5″ of rain in 24 hours in the Sac area last winter got me thinking…  I had read about the Ark Storm before.  The issue isn’t just getting to high ground.  Higher ground is also going to be hit with flash floods and potential landslides.  I can evacuate to an area of the Valley not anticipated to flood, but with potentially over a million people impacted, that’s going to cause huge stress on the system even in areas that are not flooded.  Not to mention shutting down transportation (rail tracks underwater, delivery trucks potentially unable it make it over the Sierra on either 50 or 80, etc.).  What would I even take if there was the potential to have to evacuate for months, with the possibility of having nothing left to return to?  We do carry flood insurance, and always have, despite not being in a “required” area.  And yes, the local news channels get WAY too excited every time we have a storm.  Knowing when to leave will be vital.  Likely the best anyone can do in that regard is follow the National Weather Service, who remain somewhat calmer when it rains, lol.  I think I read the modeled scenarios all take place during an El Nino year, and I believe this upcoming winter is forecast for another/continuing La Nina.  I’m also worried about increased heat for the next El Nino, since this summer actually hasn’t been too bad so far.  I suppose the only upside is that there would be plenty of advance warning for a series of ARs.

 

Hey, thanks for getting involved in the discussion! I agree with so much of what you’ve written, e.g., the way drought hampers people’s ability to absorb this threat, and the fact that “heading for the hills” just puts you in the way of landslides, mudslides, washed out bridges, etc. My family was on a ski trip, staying near Kirkwood, in late December 1996 when that big warm storm hit a big snowpack and it was absolute havoc getting back to the Bay Area— took 12 hours because we had to go east to 395 to get to 80, which was a parking lot. I can’t imagine that an ARkStorm scenario would look any better than that in the Sierra— and it would probably be worse.

If you’re in Sac, I think you just have to head for Reno and get there in advance of the weather. I remember that Nevada looked like a lake, but I don’t remember that Reno fared very badly— and it’s better than going to SF, since then you’d just be stuck with a bunch of people dealing with their own disaster and a flooded Central Valley between them and the rest of the world. I mean, as you said, there will be advance notice, you just have to know when to leave so you’re not trying to get out when 80 is a parking lot and it’s already raining.

My husband and I have been talking about it and we think we should just pick up my mom in SF and then head to Oregon on 101. I wouldn’t want to be on that road in a storm like that, but like you say, we’d have notice, and the traffic would likely not be as bad as on I-5. (Plus, I wouldn’t want to get in the way of people trying to flee the valley.) 

You’ve also spoken to two of my preliminary “when to leave” criteria: El Niño year and a forecast of multiple consecutive ARs. To that I would add normal-to-high snowpack in the Sierra (gotta be something for the rain to melt, right?) and a low pressure system in the Gulf of Alaska (though it sounds like we should be less confident in this as a factor given how the researchers simulated the event in ARkStorm 2.0?). So that’s where I’m at right now, but I haven’t read the whole article carefully (so much of my job is reading scientific papers that don’t interest me; I have quite a limited tolerance for doing so recreationally).

Glad your summer hasn’t been too bad so far. I used to live in Sac and I loved it, but summer was really rough. I grew up inside a fog bank so I really don’t do well with feeling the sun on my (pale, pale) skin. 😀

 

In the article about the big flood in 1862 they mentioned that the Indians all moved out of the Valley before the flooding. Their oral tradition told them that when ‘X, Y and Z’ occur they should expect long-term flooding. Their oral history saved them.

The articles also spoke of 30-41 days of continual rain prior to the flood.

ArkStorm also spoke of the gradually rising average temperature from global warming reducing the snow pack and replacing it with more rain. The current California water system is based on large snow pack slowly releasing water as it melts. If snow pack was partially replaced with rain it would cause much greater volumes of water coming from the mountains more quickly. The current system, even after drought would be filled quickly, too quickly. The reservoirs are not designed for a massive deluge and would need to be augmented. $$$

 

Hey, look at this: NYT is joining the fun with some sexy visualizations and “augmented reality” (that I did not try)… also good reporting about how the threat shakes out in various specific areas. Lots more here than in the WaPo article!

https://www.nytimes.com/interactive/2022/08/12/climate/california-rain-storm.html

 

Now that I’ve read the articles and several other links to forums and sites mentioned here, I must agree with the Seismologist that stated she was a 4th generation Californian and never heard of 1862 flood.  I’m a transplant that’s been here for decades through several droughts and heavy rain events and this was never referenced.  We purchased our house in 2005 after what was reported as a “100 year storm” that included mudslides and flash flooding so we knew how the area fared in these situations.  I joked that blue tarp was the latest trend in landscaping as it was so popular.  Interestingly, 2005 was not mentioned as a 100 year storm in any of these studies because it lasted only 15days.  These articles and the comments and discussion here has made me think about a long term rain event in LA.  We would shelter in place as we are on higher ground by 50m than the nearby dry river wash and dam which would fill and possibly flood. So I need to think through the duration without city services and limited access to external resources.  Home resources like solar panels wouldn’t be as helpful either.  There would be a constant water source in our downspouts at least.  

I also find it worth pointing out that that the 1862 reports indicate the native peoples evacuated.  They knew how to predict or at least recognize flood causing storms and warned the anglo people, but no further pursuit of that knowledge and oral history was included in any of these studies.  Our culture is so “not invented here” biased.   Pnwsarah, that local, historical cultural knowledge is likely what we preppers are seeking to learn – observable, clear and decisive. 

 

Totally, Alicia — I (and presumably a lot of other people) would love to know what the indigenous people of the Central Valley saw in 1862 that told them it was time to go to higher ground. Similarly, settlers could have figured out that the PNW is at risk of a megaquake/tsunami combo by talking to the indigenous people of the region about it. When academic anthropologists did bother to look into it in the late 20th century, there were tons of indigenous testimonies about the last big event in 1700.

And to your prior point, I was born in CA and have lived most of my life there, AND I have been obsessed with natural disasters pretty much since I was five, and I STILL didn’t know about the 1862 flood until that Mother Jones article came out! I can’t believe it!

 

I’d like to learn more about flooding. 🌊 I’ve never lived in a home that was prone to flooding and always thought that if a flood did happen to come by it would have to be pretty high to reach my front step.

 

A good starting point is to just type your address into this website to get an estimate for flood risk in your area.

https://riskfactor.com/

I tend to focus on the difference in elevation between my doorways and the nearest body of water. In a flooding situation, water levels can rise by several feet. So if your doorway is only 2 feet higher than a nearby lake, that lake could expand to the point where it includes your house. And yes, if you have steps leading up to your doors, that gives you quite a lot of flood protection.

 

More broadly, try finding your county on this FEMA map, then click “create report” to see a listing of the top natural hazards in your area.

https://hazards.fema.gov/nri/map#

While you can of course learn about any hazard that catches your interest, focusing on a few likely hazards for your area is more likely to pay off.

 

Thank you for the links❣️ Those were really interesting sites to look at. Luckily flooding is not a risk where I am right now, but with climate change it is predicting my chance of a fire will increase over the next thirty years.

 

Risk Factor shows my risk levels as:

Flood: 1

Fire: 2

Heat: 8

So naturally I’m putting a lot more effort into heat-related preparedness than flood. And wildfire preparedness is something I think about but haven’t put much time into yet.

FEMA ranks lightning as only my 5th highest risk. But my house was actually hit by lightning a few weeks ago, so that gets some of my attention as well. Surge protectors for everything, and I’m looking into lightning rods.

 

I think the Risk Factor site only considers Floods, Fires and Heat, not other events such as earthquakes.  For my location in LA: Heat 6, Fire 5, Flood 1.  I can believe that – we get extreme heat often so I expect it to be higher, fires have been in the actual neighborhood twice in the same year, some streets actually flood a bit every year so for some folks the flood risk is possibly higher. 

The FEMA site is a bit broader but also more questionable.  At the same location, it lists the avalanche risk is very low at 10.65.  There is no mountain looming with or without a snowcap. Compare that to the Heat Wave risk of 5.42.  We’re more likely to get an avalanche than a heat wave?  Huh?  Max risks are Earthquake is 32.16 and wildfires at 19.76.  Those make sense.  Once thing is that FEMA separates floods and riverine floods which has a small risk of 3.42.  But no risk of Drought at 0.05 while we’ve been in drought more than not in drought in the last 30 years.  

And to get back to this thread, both sites are likely underestimating the flood risk in California by not including the information from 1862 flooding and recent research into the regions historically cyclic storms and flooding.  I couldn’t tell if the Risk Factor one has done so.  

 

“The FEMA site is a bit broader but also more questionable.”

Yes, I do think there are mistakes. RiskFactor lists my heat risk as 8 (very high) while FEMA says my heat wave risk is very low. I know which of these is right, because I’m boiling in my own sweat right now. 🙂

I still find them useful as a starting point. When I first saw my area’s FEMA ratings, I thought it was strange that lightning was listed as such a high risk. A couple months later, my house was hit by lightning. I think it’s worth going through the top risks by FEMA’s estimate and perform some level of mitigation for each of them.

BTW, when I first started using RiskFactor earlier this year, they didn’t provide heat risk estimates. If they continue to expand their coverage at this pace, I’ll stop recommending the FEMA site.

 

@Eric, when I went over to RiskFactor the other day after seeing the reply in which you mentioned it, there wasn’t a heat factor for my CA address, and now there is!

Since we’re sharing, mine are as follows:

House where I live currently (PNW):

• Flood: 1
• Fire: 1
• Heat: 3 

House where I am moving in a couple of months (CA): 

• Flood: 1
• Fire: 2
• Heat: 3

PNW heat score seems low and CA flood score seems low, but otherwise these seem reasonable.

 

My flood score was low but also, seemed to be correct even with the ARKStorm data.  But that certainly changed my perspective for a vacation home or evacuation from LA location.   

 

I neglected to mention, heat (they define it as >97degF)  occurs every year to some extent here.  And so I empathize with your boiling  🙁   As FEMA goes, we’ve seen here how they can learn (consulting with TP!).  I would not be surprised if they just adopted the Risk Factor Site if it gets broad enough instead of correcting their own.