[env-trinity] CBB: Study tracks California Dryness, Recovery Challenges Back to 16th Century

Mon Apr 17 11:24:08 PDT 2017

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Columbia Basin Bulletin

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Study Tracks California Dryness, Recovery Challenges Back To 16th Century 
Posted on Friday, April 14, 2017 (PST) 

Between October 2011 and September 2015, California saw its driest four-year
period in the instrumental record, which dates back to 1895.

Parts of the state lost more than two full years of precipitation during the
prolonged, severe dry spell. But, a new study by NOAA scientists
<http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0423.1>
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0423.1 suggests that
from the longer-term view of paleoclimate records, the southern Central
Valley and South Coast parts of the state saw their worst dry spell in
nearly 450 years.

California’s hardest hit areas would likely need several decades for their
long-term average precipitation to recover back to normal levels.

This study also looked at how long it would take the state to recover from
its current precipitation deficits.

And, the scientists found that California’s hardest hit areas would likely
need several decades for their long-term average precipitation to recover
back to normal levels, starting from the 2012–2015 deficits.

“The odds of the state completely recovering from its extreme dryness within
two years are estimated at less than 1 percent,” said Dr. Eugene R. Wahl,
NCEI paleoclimatologist and lead author of the study. “But, that may be
what's happening right now if very wet conditions continue into spring.”

The extreme El Niño conditions between 2015 and 2016 helped jumpstart
recovery in the northern half of the state.

And, the scientists found that when very strong or extreme El Niño events
followed a similar deep dryness, California’s full recovery time was nearly
cut in half. 

The high amounts of precipitation California has received during the current
wet season have already set the state up for a faster recovery time than 80
percent of similar events.

If it continues to be an extremely wet year for the state, like fall 1982
through summer 1983, California would be looking at an even shorter recovery
time.

But, different parts of the state have felt the impacts of the dryness
differently, and they will likely recover at different rates. To get a
better view of these regional differences, the scientists also looked at
each of the seven standard climate divisions in California and their
histories of extreme dry spells.

In most of these regions, the scientists found that similar very dry events
had occurred since the late 16th century.

However, two of the state’s hardest hit regions—the San Joaquin Drainage and
the South Coast Drainage—likely hadn’t seen a four-year period as dry since
at least before 1571.

“These two regions include the agriculturally important Central Valley and
the densely populated greater Los Angeles and San Diego metropolitan areas,”
said Wahl, “So, the social and economic impacts are of particular importance
there.”

According to analysis of instrumental data, the Southeast Desert Basin
division had the highest likelihood of recovering within two years at around
4 percent. The San Joaquin Drainage and the South Coast Drainage divisions
effectively had a zero percent chance of recovery within two years. And, the
state's other four climate divisions ranged from a less than 0.1 percent to
around a 1.5 percent chance.

With the paleoclimate records, the results were similar for the Northeast
Interior Basins, Central Coast Drainage, San Joaquin Drainage, and South
Coast Drainage divisions. But, the likelihood of recovering within two years
dropped even lower for the North Coast Drainage, Sacramento River Drainage,
and Southeast Desert Basin divisions.

By looking at precipitation alone, the study says it provides a unique view
of California’s past climate as well as insights into its future. Under
current conditions, the scientists found that precipitation patterns alone
are capable of producing unprecedented dry conditions such as occurred in
the San Joaquin Drainage and the South Coast Drainage regions during
2012–2015, without the compounding factor of increasing temperatures.

If temperatures continue to rise as they have, says the study, the U.S.
Southwest could be facing “megadroughts” -- worse than any droughts in the
region since medieval times. In a warming world, says the study, higher
temperatures could combine with and amplify severe precipitation deficits. 

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