Posted: 05 Dec 2014 09:43 AM PST
California finally experiences the arrival of a rain-bearing Pineapple Express this week, two climate scientists from the University of Minnesota and Woods Hole Oceanographic Institution have shown that the drought of 2012-2014 has been the worst in 1,200 years. Daniel Griffin, an assistant professor in the Department of Geography, Environment and Society at the University of Minnesota, and Kevin Anchukaitis, an assistant scientist at Woods Hole Oceanographic Institution, asked the question, “How unusual is the ongoing California drought?” Watching the severity of the California drought intensify since last autumn, they wondered how it would eventually compare to other extreme droughts throughout the state’s history. To answer those questions, Griffin and Anchukaitis collected new tree-ring samples from blue oak trees in southern and central California. “California’s old blue oaks are as close to nature’s rain gauges as we get,” says Griffin. “They thrive in some of California’s driest environments.” These trees are particularly sensitive to moisture changes and their tree rings display moisture fluctuations vividly… Tree rings are a valuable data source when tracking historical climate, weather and natural disaster trends. Floods, fires, drought and other elements that can affect growing conditions are reflected in the development of tree rings, and since each ring represents one year the samples collected from centuries-old trees are a virtual timeline that extend beyond the historical record in North America. So what are the implications? The research indicates that natural climate system variability is compounded by human-caused climate change and that “hot” droughts such as the current one are likely to occur again in the future. California is the world’s 8th largest economy and the source of a substantial amount of U.S. produce.
Surface water supply shortages there have impacts well beyond the state’s borders. With an exceptionally wet winter, parts of California might emerge from the drought this year. “But there is no doubt,” cautions Anchukaitis, “that we are entering a new era where human-wrought changes to the climate system will become important for determining the severity of droughts and their consequences for coupled human and natural systems.”
Daniel Griffin, Kevin J Anchukaitis. How unusual is the 2012-2014 California drought?
Geophysical Research Letters, 2014; DOI: 10.1002/2014GL062433
Natural cycles, sea surface temperatures found to be main drivers in ongoing event
December 8, 2014
According to a new NOAA-sponsored study, natural oceanic and atmospheric patterns are the primary drivers behind California’s ongoing drought. A high pressure ridge off the West Coast (typical of historic droughts) prevailed for three winters, blocking important wet season storms, with ocean surface temperature patterns making such a ridge much more likely. Typically, the winter season in California provides the state with a majority of its annual snow and rainfall that replenish water supplies for communities and ecosystems. Further studies on these oceanic conditions and their effect on California’s climate may lead to advances in drought early warning that can help water managers and major industries better prepare for lengthy dry spells in the future. “It’s important to note that California’s drought, while extreme, is not an uncommon occurrence for the state. In fact, multi-year droughts appear regularly in the state’s climate record, and it’s a safe bet that a similar event will happen again. Thus, preparedness is key,” said Richard Seager, report lead author and professor with Columbia University’s Lamont Doherty Earth Observatory. This report builds on earlier studies, published in September in the Bulletin of the American Meteorological Society, which found no conclusive evidence linking human-caused climate change and the California drought. The current study notes that the atmospheric ridge over the North Pacific, which has resulted in decreased rain and snowfall since 2011, is almost opposite to what models project to result from human-induced climate change. The report illustrates that mid-winter precipitation is actually projected to increase due to human-induced climate change over most of the state, though warming temperatures may sap much of those benefits for water resources overall, while only spring precipitation is projected to decrease. The report makes clear that to provide improved drought forecasts for California, scientists will need to fully understand the links between sea surface temperature variations and winter precipitation over the state, discover how these ocean variations are generated, and better characterize their predictability. This report contributes to a growing field of science-climate attribution-where teams of scientists aim to identify the sources of observed climate and weather patterns. “There is immense value in examining the causes of this drought from multiple scientific viewpoints,” said Marty Hoerling, report co-author and researcher with NOAA’s Earth System Research Laboratory. “It’s paramount that we use our collective ability to provide communities and businesses with the environmental intelligence they need to make decisions concerning water resources, which are becoming increasingly strained.” To view the report, visit: http://cpo.noaa.gov/MAPP/californiadroughtreport