Decadal Signals In Precipitation

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Scott St. George

Graphics supporting a February 20 lecture at the University of Arizona's Laboratory of Tree-Ring Research.

Greg McCabe, Michael Palecki, and
Julio Betancourt, 2004:
Paciﬁc and Atlantic Ocean
inﬂuences on multidecadal
drought frequency in the
United States
PNAS 12, 4136 - 4141

Here be
decadal variability

Decadal variability in precipitation or
drought as a signal detection problem

Terrestrial climate records often
processed to emphasize D2M timescales4

1920 1940 1960 1980 2000

Decadal variance
30%

Decadal variance
5%

1920 1940 1960 1980 2000

Where is decadal variability
in precipitation strong?

Dan Cayan, Michael Dettinger,
Henry Diaz, and Nick Graham,1998:
Decadal variability of
precipitation over
western North America.
Journal of Climate 11, 3148-3166

PDSI
Temperature
Precipitation Streamﬂow
Storms
Rain/snow

Gridded (0.5 deg) monthly
precipitation, Climate Research
Unit, University of East Anglia
Period of record: 1901 - 2002

Decadal variability
Decadal variabil
Decadal varia
Decadal v

Noise
Interannual
Trend

Multidecadal
Decadal

Annual multidecadal

0% 10% 20% 30% variance

Northern California precipitation

Decadal variance = ~30 percent

“Decadal-scale ﬂuctuations are
crucial because they control water
supplies, affect biota, and may
modulate higher-frequency events
such as ﬂoods and drought.”
Dan Cayan and colleagues [1998]

Photo: California Department of Water Resources

Levee break, Sacramento basin

1915 levee break
Photo: California Department of Public Works
Courtesy Joan Florsheim

Mississippi River at Minneapolis

Photo: Mulad

Mech et al. (1987):
Does high snow over
consecutive winters have a
cumulative, negative, effect
on the viability of moose
offspring?

location and
seasonality
make a big difference
50

D2M propagates into
hydrology* and
ecology**
* clearly
** maybe
51

Is it a coincidence that D2M
variability is strongest in
the ENSO-PDO
null?
52

Thank you
Julio Betancourt Dave Meko
Julia Cole Joellen Russell
Susan Pullan Mike Wallace
Mike Mann Connie Woodhouse

Support
Manitoba Hydro
Natural Resources Canada
National Science Foundation

S co t t St. G e o r g e Toby Au lt
Geological Survey of Canada University of Arizona
sstgeorg@nrcan.gc.ca tault@email.arizona.edu

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Large-scale low-frequency variability has emerged as a priority for climate research, but instrumental observations are not long enough to characterize this behavior or gage its impacts on dependent geophysical or ecological systems. As the leading source of high-resolution paleoclimate information in the middle- and high-latitudes, tree rings are essential to understand low-frequency variability prior to the instrumental period. But even though tree rings possess several advantages as climate proxies, like other natural archives they also have their own particular impediments. In this lecture, Dr. St. George will describe the structure and characteristics of the Northern Hemisphere tree-ring width network, and outline how the fingerprint of decadal and multidecadal climate variability encoded within ancient trees varies across the hemisphere.

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In many settings, trees growing on floodplains provide an important source of indirect evidence that may be used to infer the occurrence, extent, and magnitude of floods prior to direct observations. That evidence may take several forms, including external scars caused by abrasion or impact from floating debris, anatomical changes within the annual growth increment following prolonged stem or root inundation, or tilting or uprooting due to the hydraulic pressure of floodwaters. Likely the most useful characteristic of paleoflood studies based on floodplain trees is their relatively high temporal resolution and dating accuracy compared to most other methods. Dendrochronological methods can routinely date past floods to the year of their occurrence and, in rare cases, can estimate the timing of floods that occur during the growing season to within two weeks. This high degree of chronological control, which is surpassed only by that provided by direct observation or instrumentation, can be used to determine whether floods in separate watersheds were synchronous or offset by several years and test hypotheses that suppose linkages between extreme floods and specific forcing mechanisms. Furthermore, the wide geographic distribution of tree species with dateable rings combined with the broad suite of methods available to examine interconnections between floods and tree growth allow this style of paleoflood hydrology to be applied to many settings that are not suitable for techniques that depend on geological evidence. Future paleoflood research involving tree rings will need to strike a balance between improving our understanding of the biological and fluvial processes that link tree growth to past events, and providing answers to questions about flood dynamics and hazards that are needed to safeguard people and property from future floods.

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Decadal Signals In Precipitation

1. The prominence of decadal variability in North American precipitation S c ott St. G eorge Geological Survey of Canada Toby A ult University of Arizona

3. Greg McCabe, Michael Palecki, and Julio Betancourt, 2004: Paciﬁc and Atlantic Ocean inﬂuences on multidecadal drought frequency in the United States PNAS 12, 4136 - 4141

4. Here be decadal variability Decadal variability in precipitation or drought as a signal detection problem Terrestrial climate records often processed to emphasize D2M timescales4

5. Does it matter at the regional scale? 5

6. 1920 1940 1960 1980 2000 Decadal variance 30% Decadal variance 5% 1920 1940 1960 1980 2000

7. Where is decadal variability in precipitation strong?

8. Dan Cayan, Michael Dettinger, Henry Diaz, and Nick Graham,1998: Decadal variability of precipitation over western North America. Journal of Climate 11, 3148-3166

9. Methods Photo: Christos_m2001

10. PDSI Temperature Precipitation Streamﬂow Storms Rain/snow

11. Gridded (0.5 deg) monthly precipitation, Climate Research Unit, University of East Anglia Period of record: 1901 - 2002

12. Decadal variability Decadal variabil Decadal varia Decadal v

13.

14.

15. Noise Interannual Trend Multidecadal Decadal

16.

17. What did we ﬁnd? Photo: futureshape

18. Slides missing* * Thank goodness

19. Winter decadal 0% 10% 20% 30% variance

20. Autumn decadal 0% 10% 20% 30% variance

21. Annual multidecadal 0% 10% 20% 30% variance

22. Northern California precipitation

23. Northern California precipitation Decadal variance = ~30 percent

24. D2M ‘hotspots’

25. “Decadal-scale ﬂuctuations are crucial because they control water supplies, affect biota, and may modulate higher-frequency events such as ﬂoods and drought.” Dan Cayan and colleagues [1998]

26. Decadal hotspot - Oregon/California

27. Northern California

28. Sacramento River Photo: Patty Colmer

29. Northern California

30. Northern California

31. Photo: California Department of Water Resources Levee break, Sacramento basin

32. 1915 levee break Photo: California Department of Public Works Courtesy Joan Florsheim

33. Northern California

34. Northern California

35. Decadal hotspot - Minnesota

36. Minnesota

37. Mississippi River at Minneapolis Photo: Mulad

38. Minnesota

39. Minnesota

40. Minnesota

41. Mech et al. (1987): Does high snow over consecutive winters have a cumulative, negative, effect on the viability of moose offspring?

42. Minnesota

43. Minnesota

44. Minnesota

45. Associations with major climate modes

46. It’s complicated. 46

47. Winter precipitation and the PDO

48. Winter precipitation and the PDO

49. Three main points 49

50. location and seasonality make a big difference 50

51. D2M propagates into hydrology* and ecology** * clearly ** maybe 51

52. Is it a coincidence that D2M variability is strongest in the ENSO-PDO null? 52

53. Thank you Julio Betancourt Dave Meko Julia Cole Joellen Russell Susan Pullan Mike Wallace Mike Mann Connie Woodhouse Support Manitoba Hydro Natural Resources Canada National Science Foundation

54. S co t t St. G e o r g e Toby Au lt Geological Survey of Canada University of Arizona sstgeorg@nrcan.gc.ca tault@email.arizona.edu

Decadal Signals In Precipitation

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