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Starting in the 1930s, northern California has experienced major decade-to-decade swings in the amount of precipitation that falls during winter. Is this behavior
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THE
OF NORTHERN CALIFORNIA’S WINTER PRECIPITATION
Scott St. George University of Minnesota
1Since the 1930s, northern California has experienced
extremely strong decadal variability in its wintertime hydroclimate.
2It’s not clear what’s caused this ‘seesaw’
between wet and dry winters, but it doesn’t appear to relate directly to any of the usual suspects.
3Because we don’t know
whether this behavior will continue in the near future, we should be cautious about making predictions.
Tree-ring display at elementary school
Photograph: Tom Swetnam
Northwestern Ontario
The Winnipeg River basin Northwestern Ontario
Dr. Julio Betancourt United States Geological Survey
Does low-frequency behavior in the oceans cause terrestrial climates to vary on similar timescales?
Dr. Toby Ault Cornell University
How ‘important’ is decadal variability
within terrestrial climates?
Dai, WIREs Climate Change, 2010
Sahelian Africa is probably the most decadal place on (the terrestrial part of) Earth.
More commonly, annual or seasonal precipitation has a power spectrum that resembles white noise.
total annual precipitation (mm)
Des Moines Iowa GHCN 72546000
Cayan et al, Journal of Climate, 1998
CRU TS2.1/GHCN
Ault and St. George, Journal of Climate, 2010
Averaged across all of North America, total annual precipitation exhibits a concentration of spectral power between 10 and 20 years.
0% 10% 20% 30% varianceAult and St. George, Journal of Climate, 2010
Winter precipitation along the central Pacific Coast had more variance at decadal (10-20 yr) timescales
than almost any other part of North America.
Ault and St. George, Journal of Climate, 2010
Ault and St. George, Journal of Climate, 2010
Source: Pa!y Colmer
Sacramento River northern California
Source: California Department of Water Resources
Florsheim, JL, De!inger, MD, 2007. Climate and floods still govern California levee breaks.
Geophysical Research Le!ers.
Strong decadal variability synchronizes rainfall, streamflow and hazards in northern California
Ault and St. George, Journal of Climate, 2010
1Since the 1930s, northern California has experienced
extremely strong decadal variability in its wintertime hydroclimate.
Why is decadal variability so vigorous along
the central Pacific Coast?
SST?
Ault and St. George, Journal of Climate, 2010
0 +0.2 +0.4 +0.6-0.2-0.4-0.6Correlation with the decadal component of winter precipitation
along the central Pacific Coast
Ault and St. George, Journal of Climate, 2010
The decadal component of NoCal winter precipitation shows very li!le correspondence with sea surface temperatures.
ENSO PDO AMO PNA AO NAM
r (precipitation • PDO)Ault and St. George, Journal of Climate, 2010
Northern California is located near the null region of PDO teleconnections (no consistent precipitation response)
2It’s not clear what’s caused this ‘seesaw’
between wet and dry winters, but it doesn’t appear to relate directly to any of the usual suspects.
What types of weather leads to strong variability
on decadal timescales?
Source: NOAA
[Atmospheric rivers] yield important beneficial outcomes, most particularly by providing 30%–50% of annual
precipitation and comparable fractions of overall water resources in the region
“ ”De!inger, MD, 2013, Atmospheric rivers as
drought busters on the U.S. West Coast. Journal of Hydrometeorology.
Source: NOAA
Is this behavior a stable feature of the regional climate,
or is it just a ‘passing fad’?
Source: Daniel Griffin
Decadal variability was amazingly coherent across the region during the 20th century, but…
Decadal variability was amazingly coherent across the region during the 20th century, but…
The history of meteorology is li!ered with whitened bones of claims to have demonstrated the existence of reliable cycles in the weather.“ ”
William James Burroughs Weather Cycles: Real or Imaginary?
0% 10% 20% 30% varianceAult and St. George, Journal of Climate, 2010
In most parts of North America, winter precipitation has very li!le variance at decadal (10-20 yr) timescales.
forced? stochastic?
Xiaolu (Grace) Li University of Minnesota
Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1850 -2004
Li et al., unpublished
Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1850 -2004
Li et al., unpublished
Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1001 - 1150
Li et al., unpublished
Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1451 - 1600
Li et al., unpublished
forced? stochastic?
3Because we don’t know
whether this behavior will continue in the near future, we should be cautious about making predictions.
Central Pacific Coast
