(CN) – Warming oceans and rising atmospheric climates could produce dramatic and potentially deadly shifts between severe drought periods and extreme storms in California by the end of the 21st century, according to a study released Monday.
Cycles of wet weather may become even more concentrated in winter months than they already are, while storms in the spring and fall may become less likely and less frequent, according to the report from University of California Los Angeles researchers.
“In a warmer climate, there is more water vapor in the atmosphere,” said David Neelin, an atmospheric and oceanic scientist at UCLA. “When a storm gets going, air converges at low levels carrying more water vapor with it. With more vapor to dump out, the result is more rainfall.”
The study, published in the peer-reviewed journal Nature Climate Change, sends a clear message to California officials about preparedness, according to lead author Daniel Swain, a climate scientist at UCLA.
State officials’ execution of emergency response to extreme weather events impacts the lives of 40 million Californians, wildlife and the infrastructure of a multitrillion-dollar economy.
Swain said the shifts won’t be noticeable to everyday observer of weather patterns. If you merely track statistics like average annual rainfall, “you’re missing all of the important changes in the character of precipitation,” he said in a statement.
The study also predicts an increase in the frequency of extremely dry years. Dry seasons like the ones that parched Southern California in 1976–77 and 2013–14 could increase by 50 to 100 percent.
Droughts can increase the negative impact of heavy rainfall and lead to more long-term hardship in communities across the state, including forced migration, crop loss and infrastructure damage, according to researchers.
Over the next 40 years, the state will be 300 to 400 percent more likely to experience prolonged rain storms as severe as the one that caused a now-legendary California flood more than 150 years ago, the study found.
The Great Flood of 1862 filled valleys and washed gold rush miners and their equipment out of the mountains. In the Central Valley, floodwaters stretched up to 300 miles long and as wide as 60 miles across. One-third of the state’s taxable land was destroyed, and the recently elected governor, Leland Stanford, was forced to row to his inauguration.
It could happen again, according to the study, only with more catastrophic consequences because the state is so much more populated than it was 150 years ago. In 1862, California’s population was 500,000; today, it’s close to 40 million. Cities like Stockton, Fresno and Bakersfield are situated in locales that were inundated by the legendary flood.
“We may be going from a situation where an event as big as 1862 was unlikely to occur by the end of the century to a situation where it may happen more than once,” Swain said.
The U.S. Geological Survey has a name for such an event – “The Other Big One” – and has prepared emergency planning guidelines for the storm that UCLA scientists said could happen once every 100 or 200 years.
In the world’s sixth largest economy, several massive industries — agriculture, Silicon Valley and Hollywood among them — would be brought to a standstill, the study said.
Massive flooding would likely overwhelm flood-prevention infrastructure such as levees in the Central Valley, the Los Angeles River, dams across the state and concrete waterways in urban areas, according to Swain.
“Millions of people living in the Central Valley would, at a minimum, have to leave for a while, and many could actually have their homes under 20 or 30 feet of water,” he said. “This includes much of Sacramento.”
In another key finding in the study, the increase in dramatic transitions from very wet to very dry weather is referred to by researchers as “climate whiplash.” Researchers predict a 50 to 100 percent increase in the frequency of “whiplash” events, with the greatest number of abrupt changes occurring in Southern California.
“Instead of the sporadic rains that mark the gradual onset of autumn and tapering off of spring, California will likely have a larger percentage of its annual precipitation fall during a narrower window, from December to March,” according to a UCLA news release on the study.
The onset of these weather patterns could lead to conditions where wildfires become more prevalent. Vegetation remains dry into October and November, which historically has been the early part of the rainy season.
One result could be the deadly blending of dry vegetation with warm, dry Santa Ana winds, which tend to reach peak intensity in November and December, “turning swaths of the state into dangerous tinderboxes,” the study said.
Swain said he plans to travel to Sacramento to discuss the findings with representatives of the state water board and the Public Policy Institute of California.