El Niño Doesn’t Correspond to L.A. River Flooding, La Niña Does

February 29, 2016 § 1 Comment

The interview as it appeared in Friends of the L.A. River's Current News nearly 20 years ago

The interview as it appeared in Friends of the L.A. River’s Current News nearly 20 years ago. Click to enlarge.

Something came up in a recent discussion I was having about current spate of U.S. Army Corps of Engineers make-work projects to degrade the L.A. River in the name of El Niño. If you haven’t seen it, the cutting vegetation and installing dirt-fill barriers along the edges of parts of the river, resulting in nutty bike path detours.

What makes me sad is that the L.A. River generally hasn’t flooded during El Niño years, but instead mostly during La Niña years.

I know this from an excellent interview that FoLAR bird expert Dan Cooper did with climatology professor Richard Minnich back in 1998. I ran excerpts from this in 2010 – a drier La Niña year with some big storms. Below is the whole article.

Talkin’ El Niño
An interview with Dr. Richard Minnich of University of California Riverside, by Dan Cooper

Richard Minnich is a professor of biogeography and climatology in the Department of Earth Sciences at UC Riverside. He has been studying weather patterns and landscape ecology in Southern California and Baja for the past two decades, and recently spoke with FoLAR’s Technical Advisory Board chair, Dan Cooper, in Riverside on March 6, 1998

Dan: Dr. Minnich, let’s begin with the basics – what causes flooding in L.A.?

Rich: Two components are involved, long-term and short-term causes. In the long-term, the ground has to get completely saturated by rain; water hitting dry ground won’t do a thing. Now, in the short term, it’s the hourly rates throughout the day that are important. These rates are what cause catastrophic flooding like we had in 1938.

Dan: What kind of rain are we talking about?

Rich: Ballpark rates, maybe 20 inches in a day in the Transverse Ranges (incl. the San Gabriel and San Bernardino Mtns.).

Dan: Twenty inches in one day? That’s typically what we get in a year.

Rich: In January ’43, it rained 20″ in the mountains, but it was on dry ground so nothing happened. Now downing the coastal plain where everyone lives, all that concrete has led to the potential for flash flood conditions – the water has nowhere to go but into the channels. But even without concrete, major floods are possible – the floods in ’38 occurred before the whole plain was concrete and the rivers were completely channelized.

Dan: So 1938 must have been a big El Niño year…

Rich: Pretty neutral, actually. Neither El Niño nor La Niña conditions were recorded that year. Another neutral year was the winter of 1966-67 – the Transverse Range got 30 inches in December of ’66. The Transverse Range got 30 inches in December of ’66.

Dan: So El Niños don’t coincide with flooding in the L.A. Basin?

Rich: The three spectacular El Niños we’ve seen this century have been 1940-1, 1982-3, and again in the past season [1997-8]. Not one of them caused extensive flooding in the basin.

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What’s Up with this “Dry” La Niña Year?

December 21, 2010 § 3 Comments

This year, it’s La Niña – a climate condition opposite from El Niño. I confess that I am not a climate expert and I don’t entirely understand exactly how hot and cold cycles in the Pacific Ocean actually interact with Southern California weather… but, generally, the basic equation is that El Niño brings wetter winters and La Niña brings drier ones. Various sources have been predicting a relatively dry winter. For example, this KPBS story Researchers Say Strong La Niña Means Dry Winter For California states:  “Researchers say a strong La Niña means below normal rainfall for Southern California…”

Los Angeles has experienced four consecutive days of healthy rainstorms, and a doozy predicted tomorrow. This afternoon’s L.A. Times article Strongest storm yet could bring flooding, tornadoes, hail and high winds to L.A. area predicts “thunderstorms, hail, and even waterspouts and tornadoes along the Southern California coast early Wednesday.” Could this possibly be consistent with La Niña? Well… maybe.

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