The decadal character of northern California's winter precipitation

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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 decadal character of northern California's winter precipitation

  1. 1. THE OF NORTHERN CALIFORNIA’S WINTER PRECIPITATION Scott St. George University of Minnesota
  2. 2. Since the 1930s, northern California has experienced extremely strong decadal variability in its wintertime hydroclimate.
  3. 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. 4. Because we don’t know whether this behavior will continue in the near future, we should be cautious about making predictions.
  5. 5. Tree-ring display at elementary school Photograph:Tom Swetnam
  6. 6. Northwestern Ontario
  7. 7. The Winnipeg River basin Northwestern Ontario
  8. 8. Dr. Julio Betancourt United States Geological Survey
  9. 9. Does low-frequency behavior in the oceans cause terrestrial climates to vary on similar timescales?
  10. 10. Dr. Toby Ault Cornell University
  11. 11. How ‘important’ is decadal variability within terrestrial climates?
  12. 12. Dai, WIREs Climate Change, 2010 Sahelian Africa is probably the most decadal place on (the terrestrial part of) Earth.
  13. 13. More commonly, annual or seasonal precipitation has a power spectrum that resembles white noise. total annual precipitation (mm) Des Moines Iowa GHCN 72546000
  14. 14. Cayan et al, Journal of Climate, 1998
  15. 15. CRU TS2.1/GHCN
  16. 16. 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.
  17. 17. 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.
  18. 18. Ault and St. George, Journal of Climate, 2010
  19. 19. Ault and St. George, Journal of Climate, 2010
  20. 20. Source: Pa y Colmer Sacramento River northern California
  21. 21. Source: California Department of Water Resources Florsheim, JL, De inger, MD, 2007. Climate and floods still govern California levee breaks. Geophysical Research Le ers.
  22. 22. Strong decadal variability synchronizes rainfall, streamflow and hazards in northern California Ault and St. George, Journal of Climate, 2010
  23. 23. Since the 1930s, northern California has experienced extremely strong decadal variability in its wintertime hydroclimate.
  24. 24. Why is decadal variability so vigorous along the central Pacific Coast?
  25. 25. SST?
  26. 26. Ault and St. George, Journal of Climate, 2010
  27. 27. 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.
  28. 28. ENSO PDO AMO PNA AO
  29. 29. 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)
  30. 30. 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.
  31. 31. What types of weather leads to strong variability on decadal timescales?
  32. 32. Source: NOAA
  33. 33. [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.
  34. 34. Source: NOAA
  35. 35. Is this behavior a stable feature of the regional climate, or is it just a ‘passing fad’?
  36. 36. Source: Daniel Griffin
  37. 37. Decadal variability was amazingly coherent across the region during the 20th century, but…
  38. 38. Decadal variability was amazingly coherent across the region during the 20th century, but…
  39. 39. 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?
  40. 40. 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.
  41. 41. forced? stochastic?
  42. 42. Xiaolu (Grace) Li University of Minnesota
  43. 43. Where is dec-cen variability a large component of (simulated) annual precipitation? A.D. 1850 -2004 Li et al., unpublished
  44. 44. Where is dec-cen variability a large component of (simulated) annual precipitation? A.D. 1850 -2004 Li et al., unpublished
  45. 45. Where is dec-cen variability a large component of (simulated) annual precipitation? A.D. 1001 - 1150 Li et al., unpublished
  46. 46. Where is dec-cen variability a large component of (simulated) annual precipitation? A.D. 1451 - 1600 Li et al., unpublished
  47. 47. forced? stochastic?
  48. 48. Because we don’t know whether this behavior will continue in the near future, we should be cautious about making predictions.
  49. 49. Central Pacific Coast

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