• Re: A 'megaflood' in California could drop 100 inches of rain, scientis

    From Cavemen caused global warming@21:1/5 to governor.swill@gmail.com on Sun Aug 14 04:54:16 2022
    XPost: alt.global-warming, talk.politics.guns, sac.politics
    XPost: alt.fan.rush-limbaugh

    In article <t15rrk$2qu36$115@news.freedyn.de>
    <governor.swill@gmail.com> wrote:

    Flood drown fags. Let it rain, let it rain, let it rain rain rain.


    It hasn’t happened since 1862, but California is due for another
    one

    A mention of California might usually conjure images of
    wildfires and droughts, but scientists say that the Golden State
    is also the site of extreme, once-a-century “megafloods” — and
    that climate change could amplify just how bad one gets.

    The idea seems inconceivable — a month-long storm that dumps 30
    inches of rain in San Francisco and up to 100 inches of rain
    and/or melted snow in the mountains. But it has happened before
    — most recently in 1862 — and if history is any indicator, we’re
    overdue for another, according to research published Friday in
    Science Advances that seeks to shed light on the lurking hazard.

    “This risk is increasing and was already underappreciated,” said
    Daniel Swain, one of the study’s two authors and a climate
    scientist at the University of California at Los Angeles. “We
    want to get ahead of it.”

    In such an event, some in the Sierra Nevada could end up with 25
    to 34 feet of snow, and most of California’s major highways
    would be washed out or become inaccessible.

    Swain is working with emergency management officials and the
    National Weather Service, explaining that it’s not a question of
    whether a megaflood will happen but when.

    “It already has happened in 1862, and it probably has happened
    about five times per millennium before that,” he said. “On human
    time scales, 100 or 200 years sounds like a long time. But these
    are fairly regular occurrences.”

    His paper built on the work of other scientists, who examined
    layers of sediment along the coastline to determine how
    frequently megafloods occurred. They found evidence of extreme
    freshwater runoff, which washed soil and stony materials out to
    sea. Those layers of material became buried beneath years of
    sand. The depth of the layers and the sizes of the pebbles and
    other material contained in them offer insight into the severity
    of past floods.

    “It hasn’t happened in recent memory, so it’s a little bit ‘out
    of sight, out of mind,’ ” Swain said. “But [California is] a
    region that is in the perfect area … in a climatological and
    geographic context.”

    On the West Coast, there commonly are atmospheric rivers, or
    streams of moisture-rich air at the mid-levels of the atmosphere
    with connections to the deep tropics. For a California megaflood
    to occur, you’d need a nearly stationary zone of low pressure in
    the northeast Pacific, which would sling a succession of high-
    end atmospheric rivers into the California coastline.

    “These would be atmospheric river families,” Swain said. “You
    get one of these semi-persistent [dips in the jet stream] over
    the northeast Pacific that wobbles around for a few weeks and
    allows winter storm after winter storm across the northeast
    Pacific into California.”

    The paper warns of “extraordinary impacts” and reports that such
    an episode could transform “the interior Sacramento and San
    Joaquin valleys into a temporary but vast inland sea nearly 300
    miles in length and [inundate] much of the now densely populated
    coastal plain in present-day Los Angeles and Orange Counties.”

    The effects of a month-long barrage of soaking storms could be
    disastrous, but Swain notes that it’s possible to have advance
    warning.

    “This is something we’d see coming three to five days out, and
    I’d hope a week and perhaps even two weeks out, with a
    probabilistic type of prediction,” Swain said. “We’d have a
    decent amount of warning for it.”

    Swain’s simulations showed the odds of a megaflood occurring are
    far greater in winters dominated by El Niño than in winters
    influenced by La Niña. El Niño is a large-scale chain-reaction
    atmosphere-ocean pattern that can dominate the atmosphere for
    several years at a time, and it usually begins with higher-than-
    normal sea surface temperatures in the eastern tropical Pacific.

    “When you look at the top eight monthly precipitation totals in
    simulations, eight out of eight occurred in El Niño years,”
    Swain said.

    The influence of human-caused climate change also plays a role:
    Swain says it boosts the ceiling in a megaflood.

    “We have multiple scenarios. The future one is much larger,
    consistent with [climate change],” he said. “In the historical
    scenario, the lesser one, certain parts of the Sierra Nevada see
    50 to 60 inches of liquid-equivalent precipitation … but in the
    future event, some places see 70 to 80 and a few see 100 in a 30-
    day period. Even places like San Francisco and Sacramento could
    see 20 to 30 inches of rain, and that’s just in one month.”

    An independent study published in Scientific Reports on Friday
    concluded that human-caused climate change will intensify
    atmospheric rivers and could double or triple their economic
    damage in the western United States by the 2090s.

    A warmer atmosphere has a greater capacity to store moisture. In
    the absence of storms, that means the air can more quickly dry
    up the landscape — hence California’s prolonged drought — but
    should rain occur, the deck is stacked to favor an exceptional
    event.

    “Moisture isn’t the limiting factor in California,” Swain said.
    “There’s plenty of moisture around even in the drought years.
    The absence is a lack of mechanism. It’s a lack of storms rather
    than moisture.”

    Alan Rhoades, who is an expert on atmospheric rivers and was not
    involved in either study, said the research highlights the “the
    importance of not forgetting about major flood events, which are
    also central to California’s history."

    “The major worry is how much climate change will alter the
    frequency of these event occurrences and how much it will fuel
    and amplify the impacts of the next record-setting [atmospheric
    river] event,” wrote Rhoades, a hydroclimate research scientist
    at Lawrence Berkeley National Laboratory, in an email.

    He added that compared to previous megafloods in the late 1800s,
    “California has vastly expanded its rural, urban, and
    agricultural sprawl, which could lead to more potential for loss
    of life and property.”

    While researchers can’t say when the next California megaflood
    will strike, forecasters are confident that it will happen.
    There’s a 0.5 to 1.0 percent chance of it happening in any given
    year.

    Swain said one goal of his work is to push officials to prepare.
    He suggested working with the National Oceanic and Atmospheric
    Administration to “run through simulations as a real tabletop on
    the ground disaster scenarios.”

    “We’ll work through where the points of failure would actually
    be, because one of the things we want to do is get ahead of the
    curve,” he said.

    https://www.washingtonpost.com/climate- environment/2022/08/12/megaflood-california-flood-rain-climate/

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