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Southern California Deadly Mudslides | Met Analysis

California mudslides: How it happened, is this the new norm?

Jaclyn Whittal

Wednesday, January 10, 2018, 1:58 PM - Flash floods kill more people in the United States than any other weather phenomenon, at around 100 people per year. The reason they're so deadly is that flooding happens so fast...in a flash.

Then there are landslides and mudslides. An average between 25 and 50 people are killed by these each year. Most landslide fatalities are from rock falls, debris-flows, or volcanic debris flows. Debris flows occurring in December, 2003 killed 16 people in the San Bernardino, CA, area. On Tuesday Jan 9, 2018, 13 people lost their lives due to this type of natural hazard in California. Devastating pictures and videos are coming out of southern California. The rain was a blessing in disguise -- a double edge sword, if you will. The state needed rain to help with a very active fire season, but when it  finally arrived, it became too much, too fast. 

This is what has happened in Montecito, CA, an area that averages 45 inches of rain per year. On Tuesday, with a half inch of rain falling in just five minutes and no ground soil left to help absorb the water (because of the wildfires), the affluent coastal city flooded. Badly. Portions of Highway 101 was closed, with the area looking like what some described as a 'war zone', with muddy cars floating away among large boulder rocks and other floating debris. 

Burn scars can be blamed for the mudslides and debris flows, but this story has a lot more to do with many years of weather patterns. We dive deeper into this story below.


In April 2017, California Gov. Jerry Brown declared an end to the state’s drought emergency that had drained reservoirs, devastated forests and farmland and forced millions of people to drastically reduce water use. Californians are used to drought beginning and ending. However, this one was different. This went on for over 5 years

By late 2016 and 2017 signs of a potential end to it though were on the horizon. Statistically, Northern California typically gets more rain than Southern California. The state knows this and water systems have been designed with that in mind; they move water from the Sierra into cities and farms to the south. Right on cue, in the rainy season the north got a record breaking precipitation and that water drained into many basins and just like that the drought was all over by April! Good news right? Not so fast. The rain was a blessing, until the once parched land couldn't handle any more of it... 

Watch below: Snowpack measured above normal on April 1, 2017:


Nearly 200,000 people living below America’s tallest dam -- which measures at 770 feet -- were ordered to flee their home last year as the Oroville Dam nearly was compromised, threatening locals with a wall of water flooding neighborhoods. The dam is capable of storing more than 3.5 million acre-feet which sounds like a lot and it is, but the problem is when you have a rainy season such a 2016/2017 that adds a whopping 12.8 in (330 mm) of rain in the Feather River Basin. 

Inflow of water into Lake Oroville rose from 30,000 cu ft/s on February 6 to over 130,000 cu ft/s at mid-day on February 7. This made emergency officials very nervous. Despite local officials working overtime to prevent a tragic situation flooding still materialized for many areas. 

Watch below: Gold seekers flock to Oroville dam in hope to strike it rich

The Oroville Dam area was not the only area that heavy rain fell throughout 2016/2017. As a whole California saw 30.75" of rain as numerous atmospheric river events drenched the state. It was an unusually high amount of precipitation to occur during a La Niña winter. The wettest water years in California tend to occur with El Niño conditions during the winter, while the drier years are often concurrent with La Niña winters. Either way, the significant rain had a big effect on what is playing out now. The rain allowed for the local vegetation to grow in abundance and later became fuel for major wildfires to spread.  

What is La Niña? | What is El Niño?


The wildfires of 2017 were something that many of us will remember for years to come. The scenes of people fleeing their Hollywood Hills homes with blazes surrounding them on either sides of the freeway. People trapped in their homes and many watching minute to minute as more evacuation orders were issued throughout Ventura County. The record-breaking wildfire season burnt nearly 1.4 million acres of the state

The largest fire and now the largest wildfire in California's history was the Thomas Fire. This scorched approximately 281,893 acres leaving a major void in the vegetation. This void is known as a burn scar. Burn scars are charred hillsides that have lost all their root systems and trees -- and these are what become a major mudslide hazards when heavy rain falls. Heavy rain just like on Tuesday. Let's mention it again: half an inch in 5 minutes!


We are seeing dry conditions return to the area once again in early 2018. While cold and wet conditions have enveloped the eastern United States, the Desert Southwest of the United States has been left warm and dry with constant ridging in the West. It is possible that we see more in the way of drought conditions and therefore more flooding events when the rain does come.  


Southern California and other areas of the western and central US are showing clear signs of drought as the winter progresses. Moderate drought is already affecting portions of southwest California and those numbers could rise if negative precipitation anomalies continue during the peak of the rain season, which begins now.

There are other areas that are in worse shape than California, like the Four Corners, the northern Rockies or even the Plains anywhere from the Dakotas to Texas. California, however, is more vulnerable to seeing drought grow, especially during a La Niña year when above normal temperatures and below normal precipitation is the norm during precipitation months.

Image courtesy of NOAA Precipitation probability outlook for the month of January, February and March.

The National Weather Service has been firm on predicting a scenario of this type during the next three months, which basically make up the rainy season for a large portion of the state. Snow pack is the main concern, as it is critical to the state's water supply when the dry period from late spring to fall rolls around.

STUDY: 'The Big One' puts California at risk of significant sinking

WATCH BELOW: Crushed vehicles in California after devastating mudslide

With files from The Weather Network meteorologist Caroline Floyd.

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