Superstorms and Megafloods – How Concerned Should California Be?

Science Editors’ Pick Superstorms and Megafloods – How Concerned Should California Be? Marshall Shepherd Senior Contributor Opinions expressed by Forbes Contributors are their own. New! Follow this author to stay notified about their latest stories. Got it! Aug 16, 2022, 05:14pm EDT | New! Click on the conversation bubble to join the conversation Got it! Share to Facebook Share to Twitter Share to Linkedin Flood under the Old Route 49 bridge crossing over the South Yuba River in Nevada City, California, .

. . [+] saw local and regional visitors during the atmospheric river event across Northern California on January 9, 2017.

(Photo by: HUM Images/Universal Images Group via Getty Images) HUM Images/Universal Images Group via Getty Images A new study by two very credible climate scientists warns that climate change has increased the chances of a megaflood in California. As I scoured the media landscape, I saw terms like “Superstorm” or “Megastorm” being used to describe the research. As a climate scientist, it felt appropriate to provide context on the new study and associated risks for California (and frankly other parts of the western U.

S. ). The study was recently published in the journal Science Advances and is entitled, “Climate change is increasing the risk of a California megaflood.

” Here’s my elevator ride synopsis. Using a weather model connected to a suite of climate model scenarios, the researchers assessed two “megastorm” scenarios as climate changes. Both Arkstorm scenarios were situated within El Nino conditions – anomalously warm eastern Pacific waters.

The first scenario was based on the recent past (1996 to 2005), and the second scenario was set in the 2071-2080 timeframe under a very aggressive greenhouse emission scenario, referred to as RCP8. 5 . Both cases produced megaflood outcomes associated with atmospheric rivers.

At this point, you may be thinking, “ What’s an atmospheric river (AR)? ” An atmospheric river affecting California in 2017 NASA SVS They are very narrow ribbons of moisture transport (400-600 km wind) in the atmosphere. According to a NOAA website, roughly 30-50% of annual precipitation along the U. S.

West Coast states is associated with a few AR events. Many people in the West, for example, have heard of the “ Pineapple Express . ” These AR events have a significant impact on water supply, flood hazard potential, and even snowpack after they make “landfall.

” The science of atmospheric rivers NOAA Recommended For You 1 New Research Finds A Connection Between Domestic Violence And These Two Personality Disorders More stories like this Fewer stories like this 2 This Scientist Helps Andean Forests And Ecuador’s Women In STEM More stories like this Fewer stories like this 3 Exceptional Fossil Preservation Suggests That Discovering Dinosaur DNA May Not Be Impossible More stories like this Fewer stories like this One of the study authors, University of California – Los Angeles (UCLA) climate scientist Daniel Swain tweeted, “In this work, we develop a pair of plausible extreme, month-long winter storm sequences in California—one from the recent historical climate, and one from a much warmer future climate. These sequences involve a multi-week series of successive #AtmosphericRiver storms. ” He went on to say that both the ARkHist and ARkFuture scenarios produced large precipitation amounts, but the future scenarios was 45% wetter on a statewide basis.

Amazingly, he said that some of the 30-day totals exceeded 100 inches in the future scenario. What caught my eye in the study was an increased flash flood risk. Locally, some areas were 80% wetter in the future scenario.

Swain’s Tweet thread continued, “Interestingly, we find larger increases in daily / hourly precipitation *intensities* than in overall amounts—suggesting that risk of flash flooding in smaller watersheds/urban areas, as well as debris flows, might increase more than river flood risk in warming climate. ” Beyond flooding and runoff concerns, the future scenario also produced far more rainfall than snowfall in the mountainous regions. Snowpack is vital to watersheds in the West, and this result should concern water supply managers.

So to answer the question, “How concerned should California be?” Concerned. Candidly, the concern should have been there before this study. This is just one more chip on the increasingly-loaded board.

The study clearly showed that AR systems are extreme right now and will continue to worsen. OROVILLE, CA – FEBRUARY 9: In this handout provided by the California Department of Water Resources . .

. [+] (pixel. water.

ca. gov), The California Department of Water Resources stopped the spillway flow on Thursday morning to allow engineers to evaluate the integrity of the structure after water had been released at 20,000 cubic feet per second (cfs) through the night February 9, 2017 in Oroville, California. Almost 200,000 people were ordered to evacuate the northern California town after a hole in an emergency spillway in the Oroville Dam threatened to flood the surrounding area.

(Photo by Kelly M. Grow/ California Department of Water Resources via Getty Images) Getty Images I will close with some caveats. This is one study.

However, it is certainly consistent with scientific understanding of warming-water vapor relationships and atmospheric river-climate change connections , respectively. Some critics will say, “Why do climate studies always use the worst-case RCP8. 5 scenario?” My answers is simple – it is always useful to understand the full range of possible outcomes for planning.

I suspect that most insurance companies, reinsurers, or business analysts plan with all scenarios on the table. Many climate scholars have also argued that the RCP8. 5 scenario is the “business as usual” world if we do not act to curb greenhouse gas emissions.

Others have criticized the RCP8. 5 scenario. Scenario framing is emerging as we learn more.

As imperfect (or as good) as they may be, they are useful. I will save my thoughts for another day on the term “Superstorm” within the AR context. Things are bad enough without the hyperbole.

My approach is to give a clear explanation of the “so what” factor that results when extreme rainfall becomes more extreme. That’s scary enough. Follow me on Twitter .

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