Tree Rings and Drought
Past drought on the Canadian Prairies
S co tt St. Ge orge
Geological Survey of Canada

Prairie tree-ring network, ca. 1996

3

Fort Dufferin, Manitoba

4,000 year-old
river logs
6

Prairie tree-ring network
Northern Saskatchewan
Eastern Rockies
Northwestern
Ontario
Southern Manitoba

4
Characteristics of
Prairie tree rings

The tree-ring record of summer
drought in the Canadian Prairies
Scott St. George
David Meko Greg Pederson
Martin-Phillippe Girardin David Sauchyn
Glen MacDonald Jacques Tardif
Erik Nielsen Emma Watson
Submitted to the Journal of Climate, January 2008

Tree age

Bristlecone pine
4,844 years
Source: OLDLIST
Photo: Tom Harlan

Eastern white cedar
1,653 years
Source: OLDLIST
Photo: Peter Kelly

Eastern white pine
290 years
Source: M. Girardin

Bur oak
279 years

Limber pine
846 years
Source: G. Pederson
Photo: Greg Pederson

Richard I of England 16
Photo: julie & fanu

Length of regional records
S. Alberta 480
N. Saskatchewan 169
S. Manitoba 485
NW Ontario 225
0 125 250 375 500
Years

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.
”Douglass
A.E.

Dominant seasonal signals
90
82
80
70
60
50
Sites
40
30 24
20
10 7
3
0 20
Autumn Winter Spring Summer Autumn

21

22

Medicine Hat, Alberta
Source: Environment Canada, Adjusted Historical Canadian Climate Data, 1895 – 2006

24

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/s
847 m3/s
809 m3/s
770 m3/s
823 m3/s
787 m3/s
901 m3/s
3

“Trees are not thermometers
or raingauges.”
Keith Briffa and colleagues

Quantitative drought estimates

Quantitative drought estimates

Can we
Absolutely!
do better?

Photo: Emma Watson

Photo: New York Times
38

Focus on long-term drought
100% 60% 43%
Explained variance
75%
50% 57%
40%
25%
0%
Single Year 5-Year Average

Courtesy Keith Lombardo
Measure other stuff
Wood chemistry Wood density
Stable isotopes Wood anatomy

Prairie tree rings
& drought
41

Photo: Monceau
web.mac.com/scottstgeorge