The California Super Storm??

I have been shocked the last few days at all of the media attention regarding a planning meeting discussing a “what if” scenario of a “super storm” hitting California. Here is an article all the way from the UK:

Scientists are now warning Californians that the long-awaited 'big one' earthquake could be the least of their environmental concerns.

Another more deadly threat awaits the West coast of America - in the form of a biblical ‘ARkStorm’, which could bring death and destruction on a scale never before seen.

  

Google California + super + storm yields more than 299,000 hits! And, you guessed, it “global warming” is to blame:

Weather experts say West Coast storms could get more frequent and severe with climate change. Last fall, a team of federal, state and academic experts was formed to tackle what would happen if a series of powerful storms lashed at the state for 23 days. The scenario is expected to be completed this summer and will be used in a statewide disaster drill next year.

So, we are interrupting normal blogging to look at this issue.

The Past Super Storm

Much of this speculation is centered around a major winter storm that apparently went more or less stationary in California in 1861 as described in this paper  written in 1895.  San Francisco had 35" of rain (more than a year's worth) in a month. The flooding and loss of life were catastrophic. There were reports of an "inland sea." 

There were also a number of tropical storms and hurricanes that struck California in the 19th Century:

• after October, 1854: A system considered a tropical cyclone made landfall just north of the Golden Gate.
• October 2, 1858: The 1858 San Diego Hurricane approached very close to southern California. It brought several hours of hurricane and gale-force winds to an area stretching from San Diego to Los Angeles. This storm is reconstructed as just missing making landfall, dissipating offshore.

It is important to note, as it relates to a future storm, that the 1858 storm went stationary.

There was also a period of active tropical weather in the 1930's (op sit):

• August 9, 1936: A hurricane's remnants moving north brought heavy rains to the Los Angeles area.
• September 4–September 7, 1939: The remnants of a hurricane brought over a year's worth of rain to parts of southern California.
• September 11–September 12, 1939: The remnants of a hurricane in the Gulf of California brought rain.
• September 19–September 21, 1939: A dissipated cyclone brought rain.

There are those who believe the 1936 storm was actually a hurricane in the Long Beach area. 

But, here is the key factor when it comes to these storms and earth's temperatures. World temperatures were much colder when these tropical systems occurred!

HADCRUT (British) world temperatures. Temperatures were much cooler in the mid-19th Century
and 1930's when the California tropical storms occurred. 

So, hurricanes and tropical storms do occur in California. Could it happen again? Yes, a powerful winter “cut off low” over California, followed by a strong low pressure system could cause huge rainfall and flooding.

There is a second scenario for huge wind damage and flooding rains which is a Pacific hurricane like the ones cited above. Keep in mind that California's population was a tiny fraction of today's when these earlier tropical storms occurred.  Today, the damage would be massive. 

Future Super Storm

The storm I worry most about is a marginal category 2 hurricane striking California. Low category 2 is probably the most intense hurricane that could make it to California if conditions were just right (or "just wrong"). The wind speeds at sea level are 100 mph. A category 2 hurricane’s winds, in the hills (well above sea level) could reach 115 mph. Building codes in California often specify 70 mph construction. So, thousands of homes and businesses would lose their roofs and/or suffer other structural damage, not to mention the inevitable mudslides.

The mountains of California would wring very high amounts of rain (far more than with hurricanes in the eastern U.S.) and there would be extremely severe flash flooding as the water runs across all of the pavement (rather than being absorbed in the soil). Given the population, the flooding would be far worse than in the past.  

What is the response for hurricanes?  Evacuation. Yet, if you go to the web pages of the California Emergency Management and some of the local EM’s you find no evacuation plans. The loss of life could be extremely high and there would be billions and billons of dollars in damage. 

So, I salute the U.S. Geological Survey, the State of California, and others for considering this possibility and starting to plan for it as it will eventually occur. But, tying it to global warming a scientific non-starter.