Tuesday, January 5, 2016

California Rains Are Wonderful! California Rains Are Horrible!

Car stuck in floods n Sepulveda Basin in southern California's
 San Fernando Valley on Tuesday. Photo from KTLA. 
Talk about double-edged swords: A series of storms that might last two weeks or more began in California last night.

The storms promise to drop inches and inches of rain onto the parched landscape, definitely eroding a multi-year drought, perhaps the severest in memory.

Many feet of snow will accumulate in the Sierra Nevada mountains. That's also great news: If it keeps accumulating like crazy, there will be plenty of melt water flowing from the mountains into the state's nearly empty reservoirs.

Who can complain about that?

Well, everybody. California's landscape is not good at big rainstorms. There's steep slopes that can become saturated and turn into deadly mudslides.

There's been a lot of wildfires in California in the past few years because of the drought. In areas where vegetation has burned away, there's nothing to hold the soil in place. That increases the risk of mudslides and debris flows.

Flash flooding is also common when it rains hard in California.

Ideally, the way to break the California drought is to have daily light rain and drizzle all winter to soak into the ground and restore the aquifers after such a horrible drought.

However, that's not how California winter storms work, especially in years when there's a strong El Nino, like this one.

In the short term, the first storm so far has created some local floods and mudslides and debris flows in California, but nothing hugely destructive so far.

There was flooding on the 101 Freeway, and boulders fell on the Pacific Coast Highway in Malibu Canyon, the Los Angeles Times reported. 

More flash flooding is possible Wednesday, but it looks like there might be a break in the rain over the weekend and early next week, which is a good thing.

Beyond that, the parade of storms coming off the Pacific Ocean could feature bursts of heavy rain that makes flash flooding more likely, despite the drought.

This problem could keep getting worse if the storms keep coming through the rest of January, February and into March. The steep hills will get more and more saturated, and will become more likely to give way, sending walls of mud into densely populated neighborhoods.

The damage from floods could get pretty nasty too. Everybody is especially worried about the area around Sacramento.

It's widely believed that Sacramento has the second biggest flood risk of any metro area in the nation, behind New Orleans. And we all know what happened to New Orleans when Hurricane Katrina hit in 2005.

As the Sacramento Bee put it:

"A levee breach in Sacramento could cause many deaths and cripple the economy for 1.4 million people in the metro area who depend to some degree on the city of Sacramento staying dry."

As I noted El Nino storms tend to have a lot of juice, a lot more moisture and energy than storms that happen when there's not an El Nino. You could also get a series of so-called "Pineapple Express" storms, which are basically huge atmospheric rivers that tap deep tropical moisture and spray it like a fire hose onto sections of the West Coast.

Plus, climate change has, in general, made rain storms more intense, since warmer air can hold more moisture than cooler air.

Indeed, there have been more frequent extreme floods in recent years and decades. Ask anybody in Missouri, or South Carolina, or Texas, or where I live in Vermont.

I am being all gloom and doom here, I realize. If we're lucky, if California is lucky, the floodig and mudslides won't be too bad. Maybe there will be frequent dry breaks between storms allowing the water to soak into the ground. That would help end the drought without causing too many flash floods or mudslides.

If we're lucky, California will have a gloriously wet winter without anything too extreme.

If we're lucky.

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