February 26, 2005

Torrential Rains in Southern California

Back in 2003, I recommended John McPhee's In Control of Nature as an informative look at the interaction of fire, wind, earthquakes and rain in shaping the Southern California landscape. After the huges fires of that season, heavy rains came early creating a potential for massive slides. One segment aired on the California Report said that the consequences of the fires would remain a hazard for several years.

The segment reported that the burning of the Chapparal left a thin layer of wax on the dirt that causes the dirt to be "hydrophobic". (Aside: I just love this terminology -- such compelling and vivid verbage!) This means that the land (with its very steep slopes) acts like it has been paved with a very thin layer which sluffs off water with ease, but eventually with enough water can create enomous mudslides and debris flows. Today, even though the debris basins are very large, some of them are at least 4 times smaller than they should be to protect the schools, businesses and homes below.

In the area of Rancho Cucamonga, a debris flow could create a huge disaster because of the schools in the path of the potential mudslides. The areas affected by the fire will take at least a couple of years before this thin impermiable area is broken down and the threat from debris flows will return to normal.

So here we are less than two years later where the rainfall in Southern Calfornia is greater than either Seattle or Portland in normal years and indeed, this year's total is currently the third highest LA record since people started to keep records.

So what is causing these torrential rains? Today, NOAA reports that they've identified two causes: a weak El Niņo and a blocking pattern that prevents the eastward jet stream from flowing east, keeping the water laden air hovering over Southern California.

Back in 1997, the BBC had a story about how in the future El Niņos could become a permanent part of our weather instead of only happening every 5 years likely due to global warming.

El Nino events normally occur roughly every 5 years, and last for between 12 and 18 months. However unpublished scientific research now suggests that the complex weather systems could occur every 3 years, making them a dominant weather pattern and in effect, almost permanent.

...That's a theory endorsed by Dr Russ Schnell, a scientist doing atmospheric research at Mauna Loa Observatory, 11,000 feet up on Hawaii. "It appears that we have a very good case for suggesting that the El Ninos are going to become more frequent, and they're going to become more intense and in a few years, or a decade or so, we'll go into a permanent El Nino."

Looking at NOAA's reports on El Niņos, it appears that we are experiencing weather patterns shaped more by the warming ocean temperatures without the cooling oscillation of the La Niņas. Indeed, the last La Niņa didn't show up although the scientists had been predicting its arrival in 2003. If global warming is leading to more or less permanent El Niņos, look for more brutal storms in LA's future.

Posted by Mary at February 26, 2005 03:28 PM | Environment | TrackBack(1) | Technorati links |

Dammit California, send us our rain back! We don't want to run out of water this summer!

Posted by: Seattle Girl at February 26, 2005 06:45 PM

Well, if none if the precipitation stays as snow, we'll have droughts as well.

...hmm, does ground water affect slippage along earthquake faults? Maybe--maybe not.

Posted by: Darryl Pearce at February 26, 2005 08:50 PM

Um, chapparal vegetation has evolved to burn. It's like grassland, in that the plant life of both biomes is at its optimal best when it gets burned every so often. Now granted, this may suck, human habitation-wise, but there it is.

They've got a high concentration of flammable dwellings in an area that regularly gets earthquakes and whose natural vegetation is designed to dry itself into tinder and go up in blazes every so often to germinate its seeds. Ideally, this should happen often, in which case the root systems are healthy and can still hold the soil in place.

So, in this location, with the regularly scheduled fires and frequent earthquakes, people have razed the hillsides of trees and planted thousands of tons of impermeable house on the slope instead. Then they act surprised when the hills fall down, or catch on fire, as inevitably they will given the circumstances. It entirely boggles the mind.

There are some places for which no disaster coverage (except possibly relocation reimbursement) should ever be offered to residents by insurance agencies or through FEMA. Some habitats, floodplains, natural fire zones, and soggy swamp bottoms should simply not have 'permanent' structures on them where people intend to live.

Posted by: natasha at February 27, 2005 12:00 AM