California ‘megaflood’ could leave Fresno and the Valley underwater
Californians were practically born preparing for the “Big One”.
For decades, the “Big One” has meant a giant earthquake. More recently, severe drought and wildfires have entered the scene. Now is the time to make room in the natural disaster lexicon for an extreme mega-flood. One that would leave much of the Central Valley, including Fresno, underwater.
So says a new study published by Science Advances that has received widespread media attention. Its authors claim that California is in fact overdue for a megaflood event, which they have given the biblical name “ArkStorm”. Moreover, climate change has nearly doubled the likelihood of it occurring every 25 to 50 years.
“Something that was once possible, but unlikely, in our lifetimes, has become quite likely in our lifetimes,” said Daniel Swainclimatologist at UCLA.
Using computer modeling, Swain and co-author Xingying Huang compared the results of two extreme weather scenarios: a century-long atmospheric river and another between the years 2081 and 2100. Both produced storms of a month that dumped 100 inches of rain in the Sierra foothills and even more precipitation at higher elevations.
More than enough to overwhelm our state’s water collection and delivery system and cause vast swaths of destruction.
The very idea of a mega-flood may seem inconceivable – especially during a prolonged drought – but it has happened before. Most recently in 1862, and probably five times per millennium before that, the authors said.
“On the scale of human time, 100 or 200 years sounds like a long time,” Swain said. “But these are fairly regular occurrences.”
Redux of the devastating flood of 1862?
California history buffs should already be familiar with 1862, when floods devastated Sacramento (causing widespread destruction and forcing the state legislature to pack up and move to San Francisco) and transformed much of the central valley into an inland sea.
Fresno did not become an incorporated city until 1885, 13 years after its founding as a railroad station. In 1862, there weren’t many people around.
Lucky too. Because historical accounts say the flood produced an inland sea 300 miles long and 20 to 60 miles wide that filled almost the entire central valley.
“Nearly all the homes and farms in this huge area are gone,” wrote William H. Brewer, a Yale-trained scientist hired by the state of California to study its natural resources.
“There was such an expanse of water…that the winds made high waves that tore the farms to pieces. America has never seen such flood desolation as this, and seldom has the Old World seen its like.
In his reports to the state treasurer, Brewer estimated that “more than a quarter of all state taxable property was destroyed”.
Certainly, a lot has changed since 1862. The population of the state at the time was about 500,000. Today it is nearly 40 million. We have also built a series of reservoirs, intakes, diversions and canals to store and transport water and protect against flooding.
1997 a net in comparison
These measures proved largely successful during Fresno County’s last major flood in January 1997. At the time, Millerton Lake was so flooded by the inflow of the San Joaquin River that Friant Dam operators been forced to far exceed the maximum allowable flow rate of 8,000 cubic feet per second. . At peak flow, water gushed through the dam’s four trough gates – and spilled over them – at 59,770 cfs. Almost four times the previous record.
The resulting surge wiped out a bridge in Friant and flooded the nearby San Joaquin River Hatchery as well as the Fresno County Sportsman’s Club on Lanes Road. In Firebaugh, which sits along the San Joaquin, half the town was evacuated as residents protected their homes with sandbags.
Local news reports described the 1997 flood as a “once in a century” event. But compared to 1862 and what is projected by the authors of the study, 1997 was just a trickle.
A mega-flood would not only devastate Central Valley cities such as Fresno, Sacramento and Stockton, but would also impact Los Angeles and the Bay Area. The resulting home and infrastructure losses could eclipse $1 trillion, making it the costliest natural disaster in US history.
“All major population centers in California would be affected at the same time — likely parts of Nevada and other adjacent states as well,” Swain said.
The study authors say their intention is not to cause fear and anguish, but to help state officials prepare for the mega-flood, which they say is a matter of “when ” rather than “if”.
Unfortunately, these people already have a full plate right now in the face of historically destructive wildfires, our dwindling water supply, rising sea levels, and a myriad of goals and initiatives related to climate change.
I’m skeptical of how many natural disasters and global warming crises California can realistically prepare for. But if Fresno and the Central Valley end up underwater in our lifetime, we sure would.