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

1. THE
OF NORTHERN CALIFORNIA’S
WINTER PRECIPITATION
Scott St. George
University of Minnesota

2. Since the 1930s, northern California has experienced
extremely strong decadal variability
in its wintertime hydroclimate.

3. It’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.

4. Because we don’t know
whether this behavior will continue in the near future,
we should be cautious about making predictions.

5. Tree-ring display at elementary school
Photograph:Tom Swetnam

7. Northwestern Ontario

8. The Winnipeg River basin
Northwestern Ontario

9. Dr. Julio Betancourt
United States Geological Survey

11. Does low-frequency behavior in the oceans
cause terrestrial climates to vary on similar timescales?

12. Dr. Toby Ault
Cornell University

13. How ‘important’ is
decadal variability
within terrestrial climates?

14. Dai, WIREs Climate Change, 2010
Sahelian Africa is probably
the most decadal place on (the terrestrial part of) Earth.

15. More commonly, annual or seasonal precipitation
has a power spectrum that resembles white noise.
total annual precipitation (mm)
Des Moines Iowa
GHCN 72546000

17. Cayan et al, Journal of Climate, 1998

18. CRU TS2.1/GHCN

19. 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.

20. 0% 10% 20% 30% variance
Ault 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.

22. Ault and St. George, Journal of Climate, 2010

23. Ault and St. George, Journal of Climate, 2010

24. Source: Pa y Colmer
Sacramento River
northern California

25. Source: California Department of Water Resources
Florsheim, JL, De inger, MD, 2007. Climate and
floods still govern California levee breaks.
Geophysical Research Le ers.

26. Strong decadal variability synchronizes
rainfall, streamflow and hazards in northern California
Ault and St. George, Journal of Climate, 2010

27. Since the 1930s, northern California has experienced
extremely strong decadal variability
in its wintertime hydroclimate.

31. Why is decadal variability
so vigorous along
the central Pacific Coast?

32. SST?

33. Ault and St. George, Journal of Climate, 2010

34. 0 +0.2 +0.4 +0.6-0.2-0.4-0.6
Correlation 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.

35. ENSO
PDO
AMO
PNA
AO

36. 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)

37. It’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.

38. What types of weather
leads to strong variability
on decadal timescales?

39. Source: NOAA

40. [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.

41. Source: NOAA

42. Is this behavior a stable feature
of the regional climate,
or is it just a ‘passing fad’?

43. Source: Daniel Griffin

47. Decadal variability was amazingly coherent across the region
during the 20th century, but…

48. Decadal variability was amazingly coherent across the region
during the 20th century, but…

52. 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?

53. 0% 10% 20% 30% variance
Ault 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.

56. forced? stochastic?

57. Xiaolu (Grace) Li
University of Minnesota

59. Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1850 -2004
Li et al., unpublished

60. Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1850 -2004
Li et al., unpublished

61. Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1001 - 1150
Li et al., unpublished

62. Where is dec-cen variability a large component of (simulated) annual precipitation?
A.D. 1451 - 1600
Li et al., unpublished

63. forced? stochastic?

64. Because we don’t know
whether this behavior will continue in the near future,
we should be cautious about making predictions.

65. Central Pacific Coast