Tree Rings and DroughtPast drought on the Canadian Prairies
Scott St . GeorgeGeological Survey of Canada
Prairie tree-ring network, ca. 1996
3
Fort Dufferin, Manitoba
6
4,000 year-old river logs
Prairie tree-ring network
Eastern Rockies
Northern Saskatchewan
Southern Manitoba
Northwestern Ontario
4Characteristics ofPrairie tree rings
The tree-ring record of summer drought in the Canadian Prairies
Scott St. GeorgeDavid MekoMartin-Phillippe GirardinGlen MacDonaldErik Nielsen
Greg PedersonDavid SauchynJacques TardifEmma Watson
Submitted to the Journal of Climate, January 2008
Tree age
Photo: Tom Harlan
Bristlecone pine4,844 years
Source: OLDLIST
Photo: Peter Kelly
Eastern white cedar1,653 years
Source: OLDLIST
Eastern white pine290 years
Source: M. Girardin
Bur oak279 years
Photo: Greg Pederson
Limber pine846 years
Source: G. Pederson
Photo: julie & fanu16
Richard I of England
S. Alberta
N. Saskatchewan
S. Manitoba
NW Ontario
0 125 250 375 500
225
485
169
480
Years
Length of regional records
Seasonality
”
“The trees composing the forest rejoice and lament with its successes and failures and carry year by year something of its story in their annual rings. A.E. Douglass
200
10
20
30
40
50
60
70
80
90
Autumn Winter Spring Summer Autumn
82
24
73
Site
sDominant seasonal signals
21
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Source: Environment Canada, Adjusted Historical Canadian Climate Data, 1895 – 2006
Medicine Hat, Alberta
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Effectiveness
Dendrohydrology works best where it’s
dry...
and not so well where it’s
wet
Ringwidth as a proxy for ‘Lethbridge’ PDSI
Ringwidth as a proxy for ‘Dryden’ PDSI
Uncertainty
755 m3/s847 m3/s809 m3/s770 m3/s823 m3/s787 m3/s901 m3/s840 m3/s
“Trees are not thermometers or raingauges.”
Keith Briffa and colleagues
Quantitative drought estimates
Quantitative drought estimates
Can we do better? Absolutely!
Photo: Emma Watson
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Photo: New York Times
Focus on long-term drought
0%
25%
50%
75%
100%
Single Year 5-Year Average
43%60%
57%
40%
Expl
aine
d va
rian
ce
Courtesy Keith Lombardo
Measure other stuffWood chemistry
Stable isotopes
Wood density
Wood anatomy
Prairie tree rings
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& drought
Photo: Monceau
web.mac.com/scottstgeorge