California’s drought is, if not broken, seriously dented, especially for the upcoming summer. As of Tuesday the 17th, average depth of snow in the Sierra Nevada Mountains was one and two-thirds the thirty-year average and increasing. As usual, once the media could get in, and the storms proved to be numerous and productive (and photogenic. Large bounders on the highway are cool. So are floating cars if they are somewhere far away from you,) people began trying to blame someone for the “atmospheric river.” (Climate change! Global warming! Cars and trucks! Hollywood’s moral turpitude!*) Um, well, not really. This isn’t new, just mildly uncommon.
California and parts of the western coast of North America have a Mediterranian Climate. This means that summers are warm and dry, because the ocean currents tend to be cold, and discourage evaporation. Also, winds from inland bring warm, dry air down from the mountains and push out to sea, sending any storms away from the coast. This makes for predictable seasonal weather – you can plan a picnic for July 15 and be 99% sure it will be sunny and warm, even if you set the date in December of the previous year. Likewise, November through March tend to be moist and cooler, although how wet and how cool vary from year to year. A strong La Niña pattern will send the moisture well to the north, and Seattle will get lots of snow, as will British Columbia. Southern California will be dry, and soon start worrying about water limits and rationing and Mega Drought. An El Niño year means California wades, the northern Rockies are relatively dry, and Arizona has a ski season as well as flooding. Remember when the Colorado River almost ripped out Glen Canyon Dam in the early 1980s? El Niño years. We’ve been having a series of La Niñas.
The short-term pattern his shifted, thanks to a series of Pacific storms that formed well south of the usual track in the Gulf of Alaska. These are sometimes called “the Pineapple Express,” because a southern branch of the jet stream picks them up from as far as Hawaii, and slings them over the west coast. From there they might go straight east, or north, or more rarely a little south**. They dump rain and snow on the West Coast.
Since California lives and dries by the winter rainfall and snow pack, all this would be great if it were spread out between October 1 and March 1. However, it is all in December-January, and the overload has filled rivers, flood plains, reservoirs, overloaded snow-removal equipment, and generally made a mess of the place. This is also not new. If you build a lot of hard surfaces along a river, it will rise higher and faster than before, causing flooding. Land-slides are part of the process as well, which people have observed going back to the Spanish colonial period. That’s just what the geology does in that part of the world, especially when very wet.
We’re nowhere near the mess of 1861-62 yet. Back then the Central Valley was still a wetland for the most part, undrained and grass covered, with meandering streams and only one major outlet. So when lots and lots and lots of snow and rain fell, and fell, and fell between November and January, some of it very hard and all at once, the Central Valley went under water. Literally. Sacramento was navigable by boat. Arizona, Washington, Oregon, and New Mexico also had flooding, and the Texas Panhandle finally saw the terrible drought of the 1850s broken for a while. A drought had plagued the area in the 1850s, and the shift to a very strong El Niño broke the drought hard. Very hard. Now, since there were far fewer people to be afflicted, it was a pain but not the disaster it is today. Only a few thousand people died (!) The rest of the country was more worried about the Civil War (and in TX, about the Comanches raiding again). It wasn’t that flooding hadn’t happened before, but that the scale was so impressive. Thirty-feet deep floodwaters are uncommon, and memorable. The good news was, it refilled the aquifers. The bad news was, it wiped out the ranches in the Central Valley along with a lot of other property, and cost human lives, and made a mess of the place. Wired has a pretty good article, if you skim the climate-apocalypse bits. The cautions and observations about the long-term sequence of floods and modern consequences is food for thought – and disaster novels.
Today, parts of the Central Valley have sunk from ground-water pumping. California’s water storage and use policies are . . . I will be charitable. Convoluted, awkward, complex, and perhaps slightly off in their use priorities. The current series of storms will be good in the medium-run, especially this spring and summer as the snow-pack melts and provides summer in-stream flow. Right now, it’s rough on people, livestock, and wildlife. It will also be a major concern for produce growers and other things, since so many fields are under water – literally – and will be water logged for a while. What the state of the soil will be after the water drains is to be seen. We may lose some to sand and other sediment deposits.
What we’re seeing isn’t new, just news. It’s not caused by people but by atmospheric pressure and temperature systems. Rain happens, and sometimes a lot of rain happens all at once.
*The Book of Genesis says no more global floods. There’s nothing about a localized scouring not being an option.
**The southern track is more common with El Niño patterns, and that’s where southern NM, TX, and northern Mexico get winter precipitation. Or we get it from the Gulf of Mexico, but that’s rare this time of year.