AM Best’s Review: When the Flood Comes

Featured Article – AUGUST 2011

By Matthew F. Power, President, One80 Intermediaries

Climate history study raises the specter of a repeat of a devastating California storm.

For an appropriate perspective of what may lie ahead, sometimes we have to look back first.

To truly appreciate the startling storm risk that California faces, which a new two-year study outlines, some publications and news accounts from the 19th century are tremendously instructive.

Only a smattering of details are known about the Great California Storm of 1861-1862. The state–established fewer than 12 years earlier–had a relatively small population to bear witness. A diaspora of pioneer families, prospectors and fortune seekers spanned the new territory in those early Civil War days, with only a few urban areas beginning to emerge: San Francisco, Sacramento and Los Angeles.

But in the inaugural issue of The Overland Monthly, a San Francisco-based publication created in 1868 as a counterpart to the popular Atlantic Monthly on the East Coast, a short story is set against the backdrop of one of the most significant extreme weather events in the history of North America.

The Luck of Roaring Camp, penned by Overland Editor Brett Harte, tells the story of a boy born in a southern California gold-mining camp. When the mother dies during childbirth, the miners of Roaring Camp determine to raise the child, whom they name Thomas Luck. The story’s title is ironic, as it culminates with the flooding of the foothills location of the camp in 1862 and the death of the child and everyone else in the area. The story, which became an international sensation, is a work of fiction. But, Harte accurately described the mammoth flood.

The few witnesses who did provide firsthand accounts of the storm that created the flood describe a dry and sunnystretch of weather throughout the state in the autumn of 1861 until the holiday season.

In Pioneer Notes from the Diaries of Judge Benjamin Hayes, the chronicle of a Missouri lawyer who moved to the Golden State in 1849 and became a circuit judge there, readers learn that the storm blew in gently on Christmas Day 1861. Hayes wrote: “All through the holidays there continued what we should call a nice, pleasant rain. It then rained continuously for some 15 days and nights. This was followed by a downpour of 24 hours, or longer.”

Los Angeles newspapers contain accounts of the next 25 days, during which the rains fell unabated, resulting in devastating flooding throughout the state. Flooding subsumed the entire Sacramento Valley, creating the equivalent of an inland sea passable by steamboat. The Santa Ana River turned into two large lakes covering massive amounts of land from San Bernardino well into Orange County.

For weeks, fresh water flowed into the Gulf of Farallons off the San Francisco Bay. Normal tidal flow was interrupted as a result, as the continuous ebb of fresh water 18- to 20-feet deep poured constantly into the gulf’s salt water, trapping fresh water fish in the bay for several months.

The storm, and the subsequent flooding it caused, was indeed a colossal climatological event.

Alarmingly, the U.S. Geological Survey’s recent publication, The ARkStorm Scenario: California’s Other ‘Big One,’ contends that the 1861-1862 storm was not without precedent. (AR stands for atmospheric river. See sidebar below.)


Repeat Performance

Research scientist Laurie A. Johnson, Principal, Laurie Johnson Consulting I Research for Lexington Insurance Co. and a participant in the ARkStorm Project, notes that the devastating California flooding of 1861-1862 likely was neither a freak occurrence nor the worst flooding that California has ever experienced.

“The thickness of sediment layers collected offshore in the Santa Barbara and San Francisco bays provides geologic evidence for even stronger storm episodes occurring six times over an 1,800-year period, for a mean occurrence of once every 300 years,” Johnson reported.

California’s population at the time of the storm was approximately 500,000, and the state had little established infrastructure beyond encampments, emerging townships and some nascent urban centers.

Today, with a population of more than 37 million and statewide property values in the trillions of dollars, the implications of a modern-day recurrence of that kind of storm are staggering.

The USGS estimates that despite the best efforts of flood management and disaster preparedness, a similar storm today in California would cause nearly $1 trillion in total economic damage. That would be a crippling blow to one of the world’s most productive economic engines.

Recent flooding disasters in Pakistan and Australia provide some insight into the human and economic costs associated with modern flood scenarios. The July 2010 monsoon in Pakistan caused severe flooding in onefifth of the country, affecting more than 20 million people. Australia continues to counter the effects of the momentous damage from a combined tropical cyclone and prolonged La Niña weather pattern that has generated billions of dollars in damage.

The ARkStorm study is enlightening in terms of the storm and flood risk that California faces and the measures that need to be taken to prevent economic calamity in the state if a storm similar to the 1861-1862 calamity occurs.

To accurately model the impact of a modern-day recurrence of that storm, scientists collected parametric data–precipitation, barometric pressure and wind speed–from two relatively recent storms, and then used high-resolution mapping techniques to calculate an hourly time-series across the state, portioned into fivemile-square cells. State officials, along with hydrology and flood experts, then examined and estimated the potential impact of an ARkStorm scenario.


Major Cities in Jeopardy

According to Johnson, the storm model suggests potential flooding of more than 6,000 square miles, with some areas succumbing to flood depths of 10 to 20 feet. Orange County, Los Angeles County, San Diego and the San Francisco Bay area would sustain billions of dollars in damage and a high probability of fatalities.

The USGS report notes that the economic losses resulting from such a storm scenario would include “direct costs associated with loss of building function and productivity, loss of productivity on agricultural land, reduction of lifeline services from damaged infrastructure and reductions in the labor force due to mass evacuation.”

Compounding those losses, the significant long-term impact on the state’s infrastructure and power generating systems as well as the resulting environmental damage would severely compromise the state’s ability to respond and recover.

After reviewing the ARkStorm analysis, noted climate researchers Dr. William Gray and Dr. Philip Klotzbach of Colorado State University agreed that the 1861-1862 storm conditions could recur, although they said “a scenario such as this falls well into the low frequency/high severity category.”

But, they added: “If an ARkStorm scenario were to occur on the level of the 1861 winter season, the federal government would have to respond in order to prevent a complete economic catastrophe.”

The USGS report calls for a review of current emergency response and disaster financing mechanisms to ensure that the response and recovery costs associated with a similar disaster are adequately funded.

Widespread levee failures in Hurricane Katrina influenced California voters to approve the issuance of $4.9 billion in bonds to fund levee fortification projects in the San Francisco Bay and San Joaquin Delta areas.

Tens of billions of dollars of additional funding is needed to properly protect the remainder of California against the magnitude of flooding that swallowed the state 149 years ago and that research suggests occurs every 167 years on average. Failing to make the appropriate infrastructure investments could result in damage several times that amount.

No natural disaster in modern U.S. history approaches the ARkStorm scenario in magnitude and potential for long-term economic impact. It may ultimately prove itself to be a harbinger of our national infrastructure’s most brutal test.

What Is an ARkStorm?

The AR in the term ARkStorm stands for atmospheric river. Atmospheric rivers in the Pacific consist of very wet, fast-moving air flows that are able to transport intense streams of moisture from the tropics to California. Typically, these atmospheric conveyers consist of fairly regionalized weather patterns that can persist for several days or weeks at a time.

The k in ARkStorm represents the number 1,000, referring to the risk of such a severe climatological event occurring over a 1,000 year period. Atmospheric river-generated storms have been recorded five times in California since the 1930s, but none have approached the intensity and sustained duration of the 1861-1862 storm.


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