As soon as the National Oceanic and Atmospheric Administration (NOAA)
released climate data for the summer of 2014, the two scientists sprang
into action. Using their blue oak data, they reconstructed rainfall back
to the 13
th century. They also calculated the severity of
the drought by combining NOAA's estimates of the Palmer Drought Severity
Index (PDSI), an index of soil moisture variability, with the existing
North American Drought Atlas, a spatial tree-ring based reconstruction
of drought developed by scientists at Columbia University's
Lamont-Doherty Earth Observatory. These resources together provided
complementary data on rainfall and soil moisture over the past
millennium. Griffin and Anchukaitis found that while the current period
of low precipitation is not unusual in California's history, these
rainfall deficits combined with sustained record high temperatures
created the current multiyear severe water shortages. "While it is
precipitation that sets the rhythm of California drought, temperature
weighs in on the pitch," says Anchukaitis.
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.
http://www.sciencedaily.com/releases/2014/12/141205124357.htm
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