What could be "worse" than a megadrought in California? How about a "megaflood"

 

Although it appears that we won’t have any 100 degree days like last summer here in the Seattle area, for August the forecast indicates that every day this month will see high temperatures of 80+ degrees with a few 90+ days thrown in there, and not a drop of rain in sight. As I’ve posted before that doesn’t mean we are in drought conditions, since we are still well above the normal precipitation expected for the year at this point, and it is nice to have some dry weather for a change.

So it is within reason to speculate that we are in the midst of climate change and global warming, right? Well, that wouldn’t be obvious if the well-below normal temperatures and above normal precipitation during the spring and most of June was any indication, although this was explained by unusual air pressure pushing the Polar Vortex further south. But in general we seem to be having a better time of it than some other places, like parts of California that have seen years and even decades of drought conditions, to the point it is referred to as “megadrought.”

So when is it going to end? Not sure, but it could get worse before it gets better. In fact California may be in for something that it hasn’t been seen in 160 years: a “megaflood.” This old map shows a massive 300-mile long inland “lake” in the central valleys and flooding along some coastal regions…

 

…and this is from a journal covering the event:

 

A megaflood like this would occur during a month-long succession of atmospheric rivers, which are bands of air that are heavily-concentrated with water vapor, which must be released somewhere. In the Pacific Northwest we encounter these “rivers” a few times a year, but never for more than a few days with the accompanying cresting of rivers and creeks. But we are told that because global warming has rapidly increased, the probability of a megaflood event happening sooner than later in California is higher, and with greater severity, since warmer air holds more water. While serious flooding events have occurred from time to time and are natural occurrences, the possibility of more serious events being more frequent would have particularly dire consequences.

To quote from a CNN story a few days ago in regard to the 1861-62 megaflood event,

Some areas had up to 30 feet of water for weeks, obliterating infrastructure, farmland, and towns. Sacramento, the new state capital at the time, was under ten feet of debris-filled water for months.The catastrophe began in December 1861, when nearly 15 feet of snow fell in the Sierra Nevada. Repetitive atmospheric rivers dropped warm rain for 43 days thereafter, dumping water down the mountainous slopes and into the valleys. Four thousand people lost their lives, one-third of the state’s property was destroyed, a quarter of California’s cattle population drowned or starved, and one in eight homes were a complete loss by floodwaters. In addition, one-fourth of California’s economy was obliterated, resulting in a state-wide bankruptcy.

A just released Science Advances study warns that a similar or worse event occurring in California would be much more catastrophic than a massive earthquake, and five times more costly than Hurricane Katrina. A loop that was created for the study shows the west coast as a massive atmospheric river event approaches…

 

…begins flooding events near the coast and dumping heavy snowfall in the mountains to the east of the Central Valley...

 

…and then causes various degrees of flooding over most of the state, virtually “obliterating” it with water:

 

Because the air carrying this moisture is warm, snow melt in the mountains occurs faster and what falls as snow occurs only at increased elevations.  The Science Advances study (which, to be honest, isn’t easy to fully comprehend) has several scenarios (none of them good) for major precipitation events, but the one that specifically speaks to the variables leading to a megaflood event notes this effect by atmospheric rivers on snow fall, which is serious because snow pack in the mountains is itself a “reservoir” of water held in reserve.

Water managers in drought-stricken California may “rejoice” when an atmospheric river results in man-made reservoirs like Lake Powell suddenly filling with water, but the rapid increase of water over a short period of time—which is predicted to produce double or even quadruple the runoff than the previously recorded megaflood—means the flow of water will be much more difficult to control, particularly where it goes and what damage it causes. With less snow pack, there will be less water in “reserve” when drought conditions return.

We are told that California is “overdue” for a megaflood event, and because there is so much more to reap destruction on, one can only imagine its effect not just on the state, but the country as well. The SA study suggests that “natural variation” has forestalled such an event, but this can only be a temporary “fix.”  Because of the effect of global warming, this is more like a damaged dam that has been eaten away out of sight below the waterline but has managed to hold on until that one massive surge of water that it isn’t strong to hold back breaks through.