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Sierra snowpack lowest in 500 years; a wet winter won’t save California

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Sierra Nevada snowpack lowest in five centuries

Posted: 14 Sep 2015 08:45 AM PDT

Snowpack in California’s Sierra Nevada in 2015 was at the lowest level in the past 500 years, according to a new report. The research is the first to show how the 2015 snowpack compares with snowpack levels for the previous five centuries.
“Our study really points to the extreme character of the 2014-15 winter. This is not just unprecedented over 80 years — it’s unprecedented over 500 years,” said Valerie Trouet, an associate professor of dendrochronology at the UA Laboratory of Tree-Ring Research. “We should be prepared for this type of snow drought to occur much more frequently because of rising temperatures,” Trouet said. “Anthropogenic warming is making the drought more severe.” California’s current record-setting drought began in 2012, the researchers note in their report.

On April 1 of this year, California Gov. Jerry Brown declared the first-ever mandatory water restrictions throughout the state while standing on dry ground at 6,800-foot elevation in the Sierra Nevada. The historical average snowpack on that site is more than five feet, according to the California Department of Water Resources. The lack of snow in 2015 stems from extremely low winter precipitation combined with record high temperatures in California in January, February and March, Trouet said. About 80 percent of California’s precipitation occurs in the winter months, she said. Snowpack level is generally measured on April 1 each year, a time when the snowpack is at its peak. “Snow is a natural storage system,” she said. “In a summer-dry climate such as California, it’s important that you can store water and access it in the summer when there’s no precipitation.” In past years the snows of the Sierra Nevada slowly melted during the warmer months of the year, and the meltwater replenished streams, lakes, groundwater and reservoirs. In a winter with less snow or with winter precipitation coming as rain rather than snow, there is less water to use during California’s dry summers….

 

Soumaya Belmecheri, Flurin Babst, Eugene R. Wahl, David W. Stahle, Valerie Trouet. Multi-century evaluation of Sierra Nevada snowpack. Nature Climate Change, 2015; DOI: 10.1038/nclimate2809

 

 

National Geographic graphic

A Wet Winter Won’t Save California

By NOAH S. DIFFENBAUGH and CHRISTOPHER B. FIELD SEPT. 18, 2015 NYTimes Opinion

Noah S. Diffenbaugh is an associate professor of earth system science at Stanford. Christopher B. Field is director of the department of global ecology at the Carnegie Institution for Science.

STANFORD, Calif. — As wildfires rage, crops are abandoned, wells run dry and cities work to meet mandatory water cuts, drought-weary Californians are counting on a savior in the tropical ocean: El Niño.

This warming of the tropical Pacific occurs about every five years, affecting climate around the globe and bringing heavy winter precipitation to parts of California. The state experienced two of its wettest years during two of the strongest El Niños, in 1982-83 and 1997-98. Now climatologists have confirmed that a powerful El Niño is building, and forecasts suggest a high likelihood that El Niño conditions will persist through the next several months. So we in California expect a rainy winter. But before everyone gets too excited, it is important to understand this: Two physical realities virtually ensure that Californians will still face drought, regardless of how this El Niño unfolds.

Our research has shown that global warming has doubled the odds of the warm, dry conditions that are intensifying and prolonging this drought, which now holds records not only for lowest precipitation and highest temperature, but also for the lowest spring snowpack in the Sierra Nevada in at least 500 years. These changing odds make it much more likely that similar conditions will occur again, exacerbating other stresses on agriculture, ecosystems and people. At the same time, extreme wet periods may also increase because a warming atmosphere can carry a larger load of water vapor. In a possible preview, persistent El Niño conditions this year could force Californians to face both flooding and drought simultaneously. The more rainfall there is, the more water will be lost as runoff or river flow, increasing the risk of flooding and landslides. Add in the fact that the drought and wildfires have hardened the ground, and a paradox arises wherein the closer El Niño comes to delivering enough precipitation to break the drought this year, the greater the potential for those hazards. In the United States, we experienced more than 80 “billion-dollar” climate and weather disasters in the last decade, and several have cost much more. The regularity of these episodes and the resulting damage shows that we are not prepared for the current climate, let alone a changing one that portends more weather extremes. From these disasters, we can take away two lessons: Increasing resilience now can build protection for the future, and stressed systems are more prone to disasters. For instance, the risk from a period of extremely low water supply in California is far greater when high temperatures, like those we’ve seen here over the last two years, prolong drought. There are also risks when the combined demands of households, manufacturing, farming and ecosystems tax water supplies even in good years, or when forest management practices create conditions that fuel fires. Californians will benefit by reducing these interacting stresses. We are not arguing that the drought has been caused by climate change alone, or that all weather disasters have a link to climate change. However, the evidence is clear that many areas of the globe are experiencing increasing risks from weather and climate hazards. As with the California drought, climate change is an important thumb on the scale, increasing the odds of particular extremes in specific places. In California, we can expect warmer winters and hotter summers, drier dry years and wetter wet years, and less water storage from snowpack in the mountains, which also controls flooding. This means more years with extreme fire danger, critically overdrawn groundwater, legal water rights that exceed the amount of water available and challenges to balancing trade-offs among water storage, flood control and environmental protection. We have opportunities to rethink the fundamental structure of water rights and markets, re-engineer water storage to compensate for decreasing snowpack, update regulations and infrastructure to embrace water reuse and recycling, and regulate end-user pricing to encourage conservation. In short, we benefit from incorporating climate-related risks in planning for California’s future. Fortunately, California has many assets, including historical experience, robust institutions, sophisticated science and engineering expertise and financial flexibility. Capitalizing on these assets can reduce risks today and set a path for a vibrant future. Doing so will begin by acknowledging that we are already living in a rapidly changing climate.

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