Thursday, March 23, 2017

Climatologist sees intense drought punctuated by wet conditions as new normal

Stanford University climatologist Noah Diffenbaugh sees no contradiction in California, on the US West Coast, experiencing one of its wettest years on record right on the heels of a record-setting extended drought.

"We are now in a very different climate, one where we're likely to experience more frequent occurrences of hot, dry conditions punctuated by wet conditions. That's not the climate for which our water system was designed and built," said Diffenbaugh, a professor of Earth System Science at Stanford's School of Earth, Energy & Environmental Sciences.

Asked "why did California receive so much rain lately if we're supposed to be in the middle of a record-setting drought?" Diffenbaugh often refers the questioner to a Discover magazine story published in 1988, when Diffenbaugh was in middle school, and written by veteran science writer Andrew Revkin, which detailed how a persistent rise in global temperatures would affect the Golden State's water system.

The article predicted that as the largest state in the United States warmed, more precipitation would fall as rain rather than snow, and more of the snow that did fall would melt earlier in the season, cause reservoirs to fill up earlier, increasing the odds of both winter flooding and summer droughts.

"It is amazing how the state of knowledge in 1988 about how climate change would affect California's water system has played out in reality over the last three decades," Diffenbaugh, who specializes in using historical observations and mathematical models to study how climate change affects water resources, agriculture, and human health, was quoted as saying in a news release from Stanford.

"When you look back at the historical record of climate in California, you see this pattern of intense drought punctuated by wet conditions, which can lead to a lot of runoff," said Diffenbaugh. "This is exactly what state-of-the-art climate models predicted should have happened, and what those models project to intensify in the future as global warming continues."

Viewed through this lens, the recent disastrous flooding at Oroville Dam and the flooding in parts of San Jose in California as a result of the winter rains could foreshadow what's to come. "What we've seen in Oroville and in San Jose is that not only is our infrastructure old, and not only has maintenance not been a priority, but we're in a climate where we're much more likely to experience these kinds of extreme conditions than we were 50 or 100 years ago," he said.

And, the intensifying cycle poses risks in the decades ahead. "In California and throughout the Western US, we have a water system that was designed and built more than 50 years ago," the climatologist said, noting that it is not too late for California to catch up in its preparations for a changing climate.

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