BY MIKE MAGEE

On September 25, 1939, Southern California woke with fear of The Lash of St. Francis or El Cordonazo on the horizon. The term refers to northwestern tracking, cyclone-laden storms that can hit the western shores of Mexico and California most commonly around the Feast of Saint Francis, on October 4th. This one made landfall at San Pedro, California.

The calamity that day in Southern California was a rare event, the only one of its kind in the 20th century. The last one to hit, prior to this was in San Diego on October 2,1858. The Earth’s rotation normally assures that such cyclones in this region move from east to west, and out to sea. But the 1939 storm was the exception, and the big problem was the rain, some 5 1/2 inches over a 24-hour period (though the town of Indio, in the Coachella Valley of Southern California’s Colorado Desert region experienced 7 inches and buried the valley in 4 feet of water. Forty-five died on land, and 48 perished at sea. One positive – the storm marked the end of a 1-week heat wave where Los Angeles reached 107 F degrees and claimed 100 lives.

History repeated itself 84 years later this weekend, with a memorable “Lash” on the backend of a summer heat wave. The human, economic, and ecological tolls remain to be calculated. But one thing is for certain, global warming has arrived, and with it the production of both heat and water and a new, all too familiar meteorological phenomenon, the “atmospheric river.”

NOAA defines “atmospheric river” this way: “Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics. While atmospheric rivers can vary greatly in size and strength, the average atmospheric river carries an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. Exceptionally strong atmospheric rivers can transport up to 15 times that amount. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow.”

To be clear, these drenching above-ground collections of water are generally a blessing because they provide most of the much-needed precipitation to California’s dry areas and replenish the water cycles in the region. But as the Earth has warmed, they more frequently represent “too much of a good thing”, and are now responsible for 90% of California’s flood damage.

NASA reports that “the increases in water vapor are a consequence of global warming. Higher temperatures increase the evaporation of water over land and sea. The warmer area holds onto more water vapor, and slows down condensation and precipitation. The trapped water floating in the sky absorbs even more heat, which in turn attracts even more water vapor – creating a disastrous “positive feedback loop.”

By sucking up water vapor, the phenomenon makes dry regions drier, and by forming and dumping the “rivers”, creates wetter wet regions and tragic flooding. Specifically, here are five predictable repercussions of human behavior-induced alterations in global atmospheric health.

1. Heavier Rainfall: For every 1 degree Celsius (1.8 here F) rise in atmospheric temperature, the air is able to absorb 7% more water. Since the pre-industrial revolution, the atmospheric temperature has risen 1.3 degrees Celsius. By the end of this century, if trend lines are uninterrupted, rainfall amounts could increase up to 60% over current levels.

2.  Massive Infrastructure Destruction: Flood damage in the billions is nearly certain as storms become more intense, prolonged, and closer spaced. Atmospheric river events could increase three or four-fold compared to pre-industrial times. Expect an additional $1 billion in flood damage for every 1 degree Celsius rise in temperature.

3. Diminished Snowpack Reserves: Atmospheric rivers are associated with less snowfall in western U.S. mountain ranges. Intense rainfall on existing snow accelerates melting and extreme flooding from rapid water runoff. Termed “rain-on-snow” events, areas at greatest risk are the Canadian Rockies, the Sierra Nevada, and the Colorado River network.

4. Geographic Shifts: Warmer atmospheres show signs of altering the jet stream, pushing it closer to the equator. Experts have predicted that this will result in the winter expansion of atmospheric river events in Southern California. Paradoxically, soils are drying out due to increased soil evaporation, less snowpack cover, and erosion from rapid downpours.

5. Loss of Sea Ice: Recent studies reveal that shrinking ice cover in the Artics is not simply a function of warming temperatures. A new contributor is that the atmospheric rivers are increasingly moving north toward the Arctic Pole. It is now believed that the resultant water on ice is responsible for at least 1/3 of the loss of winter ice. They do this not only by the melting effect of direct water on ice over 10 days following each downpour but also by magnifying “downward longwave radiation”

As this most recent weather calamity confirms, human-instigated extreme climate-driven events are now inescapable in the short term. This storm is currently dumping 3 to 6 inches across the region, with 10 inches in some locations coming close to overwhelming the deep LA water trenches. Equally evident is that our modern (and aging) infrastructure – including roads, spillways, bridges, dams, building codes, and rescue and safety operations – require a rapid redesign.

Mike Magee MD is a Medical Historian and regular THCB contributor. He is the author of CODE BLUE: Inside the Medical Industrial Complex.