future climate scenaria in California predict increased volatility, with atmospheric rivers playing a crucial part.
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California, a state known for its diverse landscapes and Mediterranean climate, is experiencing a shift in its precipitation patterns. A series of studies led by researchers at the University of California San Diego have shed light on this change, revealing a trend towards more volatile and extreme weather events.
During the winter of 2017, California witnessed over thirty atmospheric rivers, three of which were categorized as "extreme." Atmospheric rivers, responsible for 40 to 50 percent of California's annual precipitation in some years, are long, narrow bands of water vapor that travel along the West Coast.
However, a long-term drying trend has been observed on the West Coast, particularly in terms of the frequency and average precipitation contributions from atmospheric rivers. For instance, Oregon’s atmospheric river precipitation rates have decreased by over 2 millimeters per decade since 1980.
This changing pattern is influenced by regional shifts in atmospheric circulation, which reduce the frequency of typical atmospheric river events and cause long-term winter drying on the West Coast. Yet, it also increases the occurrence of extreme, catastrophic atmospheric river events, which tend to cause intense, localized flooding.
The long-term increase in water vapor transport is linked to warming ocean temperatures and increased atmospheric moisture capacity. However, this increase is partly counteracted by changes in atmospheric circulation, leading to a reduction in regular atmospheric river frequency on the West Coast.
These findings have significant implications for California's water resources. The long dry periods between storms allow toxins and pollutants to accumulate on the land surface, increasing the risk of toxic runoff into the ocean and affecting coastal ecosystems and human health.
The research, published in the journals Geophysical Research Letters and Scientific Reports, suggests that California's precipitation regime is becoming more volatile, with intense "atmospheric rivers" and longer dry periods. Despite these challenges, the studies indicate that California is not likely to run out of water in the long term.
The work was funded by the Department of the Interior, the California Department of Water Resources, and NOAA's California and Nevada Applications Program. The catalog of atmospheric river history along the West Coast, created by the research team, provides clues as to how scientists could use the climate variability patterns identified to forecast atmospheric river activity at seasonal timescales.
In summary, California's precipitation pattern is evolving, with less frequent but potentially more intense extreme precipitation events. This change is linked to anthropogenic thermodynamic processes driven by warming sea surface temperatures and rising atmospheric water-holding capacity, but regional shifts in atmospheric circulation partly counteract this trend. The future holds challenges for water resource management, but the state is not expected to face a long-term water scarcity.
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