A team of scientists at Stanford University on Thursday reported that the lingering California drought is “very likely” linked to human-caused climate change.
The new study, led by Stanford climate scientist Noah Diffenbaugh, used a combination of computer simulations and statistical techniques to demonstrate that a persistent region of atmospheric pressure hovering over the Pacific Ocean near the Western Hemisphere has diverted storms away from California and is much more likely to form in the presence of large concentrations of modern greenhouse gas.
“Our research finds that extreme atmospheric high pressure in this region—which is strongly linked to unusually low precipitation in California—is much more likely to occur today than prior to the human emission of greenhouse gasses that began during the Industrial Revolution of the 1800s,” Diffenbaugh said.
When combined with unusually warm temperatures and stagnant air conditions, the study suggests that the lack of rainfall has triggered an increase in wildfires and increased air pollution throughout the state. Another report this week, this time from the National Drought Monitor, said the water shortage may result in direct and indirect state agricultural losses of at least $2.2 billion, and may lead to the loss of more than 17,000 seasonal and part-time jobs this year. Such impacts have prompted Gov. Jerry Brown to declare a drought emergency, and encourage the federal government to designate all 58 California counties as “natural disaster areas.”
Researchers at the National Science Foundation reported this week that the immediate cause of the drought is a “particularly tenacious” trough or “blocking ridge” over the northeastern Pacific Ocean—popularly known among meteorologists as the “Ridiculously Resilient Ridge”—that has prevented winter storms from reaching California during the 2013 and 2014 rainy seasons. Scientists explain that while these “blocking ridges” occur periodically at certain temperature latitudes (depending on the distance from the equator), the aforementioned “Triple R” was exceptional for both its size and longevity. While it dissipated briefly during the summer months of 2013, it returned even stronger last fall, lasted throughout the winter and resulted in no rainfall and little snowpack during the state’s traditional rainy season from February through May.
Swain explained the atmospheric phenomenon as similar to a “large boulder” that has, somehow, tumbled into a narrow steam and has diverted the flow of high-speed air currents known as the jet stream far to the north, thereby causing Pacific storms to bypass not only California, but also Oregon and Washington. Therefore, rain and snow that would normally fall on the West Coast were instead re-routed to Alaska and as far north as the Arctic Circle.
