New study links climate change and California's exceptional drought conditions

Monday, September 29, 2014, 4:10 PM - While it's not easy isolating man-made climate change as the specific cause of any particular extreme weather event, a new study from Stanford University has done just that, with the weather conditions that produce the extreme drought in California.

California's persistent drought, which is one of the worst the region has ever experienced, now has at least 80 per cent of the state under extreme drought conditions or worse, and nearly 60 per cent of the state under the worst conditions - 'Exceptional Drought'. Compared this to just one year ago, when, when over 86 per cent of the state was only at the level of 'severe drought' or worse, and nowhere had yet reached 'exceptional drought', and you can see just how bad things have gotten.

Credit: Richard Heim, NOAA/NCDC

Normally, California receives ample rainfall and snowfall, so that its mountains are snow-capped nearly all year long and there is abundant water to meet the needs of agriculture and urban communities. So, what's behind the lack of precipitation in the state these past couple of years?

According to a new study, it's due to a strong high pressure area over the northeastern Pacific Ocean, off the coast of British Columbia and Alaska. Whereas storms coming up from the central Pacific before had little trouble making it to the California coastline, the clockwise rotation of air around this persistent high pressure are diverting nearly all the storms off to the north.

CLICK BELOW TO WATCH: Stanford climate scientist Noah Diffenbaugh and graduate student Daniel Swain explain the 'Ridiculously Resilient Ridge' that is responsible for California's drought conditions.

The video, which was recorded in February of 2014, did not include the latest conditions that were being reported in California at the time this study was published, on Sept 29, 2014. A quick comparison to the U.S. drought maps used in the video to those pictured above show the extreme difference over just the past seven months. Also, some storms did make it through the weakened high, as Swain mentions, but when they did, they caused devastating floods due to the effects of all the precipitation falling on parched ground that just couldn't handle the sudden deluge of water.

The reason for all of this? After examining how often this 'Triple R' (as Diffenbaugh and Swain call it) has happened in the climate record, the study team combined statistical methods with models of past and current climate to produce their results.

"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 gases that began during the Industrial Revolution in the 1800s," Diffenbaugh said in a Stanford press release.

According to the release, the atmospheric conditions associated with this 'Triple R' - which are consistently linked to unusually dry conditions in California - are at least three times as likely to occur now as they were to occur prior to the start of the industrial revolution.

"In using these advanced statistical techniques to combine climate observations with model simulations, we've been able to better understand the ongoing drought in California," Diffenbaugh added in the release. "This isn't a projection of 100 years in the future. This is an event that is more extreme than any in the observed record, and our research suggests that global warming is playing a role right now."