In this presentation, we use tree rings (continuous and discontinuous series) to reconstruct past spring floods in cold environments. Spring floods are short duration events that may not be visible in classical tree ring indicators such as ring widths. Ice scars are conspicuous evidences of past spring floods and can greatly augment the reconstruction’s reliability, but pose a certain number of statistical problems when they are used as proxies. Some of these problems are described and solved here, using a novel reconstruction procedure.

1. É"enne
Boucher
Taha
B.M.
J.
Ouarda
Yves
Bégin
Antoine
Nicault
Ins<tut
Na<onal
de
la
Recherche
Scien<fique
Centre
Eau-­‐Terre-­‐Environnement
boucher@cerege.fr
Photo
credit:
S.
Popov
World
Dendro
2010,
Rovaniemi,
Finland

2. Why
reconstruct
spring
floods?
Hudson
bay
LA
GRANDE
(LG)
hydroelectric
complex

3. Why
reconstruct
spring
floods?

4. Infilling
of
hydroelectric
reservoirs
Spring
Why
reconstruct
spring
floods?
boucher@cerege.fr

5. Pros
Cons
A
mul<-­‐proxy
dendrohydrological
approach
to
reconstruct
spring
floods
Discon<nuous
series
/
uncertain<es
/
non-­‐lineari<es
Direct
rela<onship
with
streamflow
Con<nuous
series
Indirect
rela<onships
with
streamflow

6. Discrete
event
series
e.g.
ice
scarred
trees

7. Uncertain
discrete
series
[0.05,
0.5,
0.95]
Propor<on
of
ice-­‐scarred
trees
around
a
northern
lake
Propor<ons
N
trees
sampled
boucher@cerege.fr

8. Model
uncertain"es
of
discrete
event
series
Uncertain<es
around
observed
propor<ons
are
binomialy
distributed
1)
Model
verifica"on
Jackknife
resampling
3)
Calibra"on
/
Reconstruc"ons
Performed
using
Generalized
Addi<ve
Models
(GAMs)
2)
€
g(E(Q)) = B0 + f1TR1 + f2TR2 + ...
boucher@cerege.fr

10. Reconstruc<on
of
May
water
supplies
to
the
Caniapiscau
reservoir
(northern
Québec,
Canada)
boucher@cerege.fr

11. Hudson
bay
La
Grande
HE
complex

12. Dendrochronological
data
=
Earlywood
density
=
Ice
scar
chronology
at
lake
Montausier
boucher@cerege.fr

13. Water
supplies
to
the
Caniapiscau
reservoir,
&
hydrological
variables
to
reconstruct
boucher@cerege.fr

14. Discrete
and
con<nuous
dendroseries
Propor<on
of
ice
scoured
trees
around
lake
Montausier
Earlywood
density,
PC1
Earlywood
density,
PC2
boucher@cerege.fr

15. The
Montausier
lake
ice
scar
chronology
(an
other
look
at
it…)
Propor<ons
N=300
boucher@cerege.fr
For
each
year,
N=300
possible
propor<ons
were
randomly
generated
from
a
binomial
distribu<on.
Colors
indicate
«
the
number
of
"mes
a
simulated
propor<on
value
falls
in
each
class
»

16. Rela<onships
between
TR
series
&
water
supplies
(QMay)
to
the
Caniapiscau
Reservoir
Propor<ons
of
ice
scarred
trees,
Montausier
lake
PC1
Index
(wet
sites)
PC2
index
(mesic
xeric
sites)

17. Calibra<on
/
verifica<on
sta<s<cs
&
comparison
with
a
tradi<onal
MLR
approach
€
g(E(QMay )) = B0 + f1X1 + f2X2 + ...
€
E(QMay ) = B0 + B1X1 + B2X2 + ...
+
boucher@cerege.fr

18. Historical
May
water
supplies
to
the
Caniapiscau
Reservoir
boucher@cerege.fr

19. Discussion
and
Conclusion
-­‐ A
new
approach
to
reconstruct
paleofloods
from
tree
rings
in
northern
environment.
It
allows:
1) to
take
advantage
of
both
discrete
and
con"nuous
tree
ring
proxys
2) to
model
and
include
the
uncertainty
of
discrete
TR
series
within
the
calibra<on
/
reconstruc<on
process
3) to
account
for
non-­‐linear
rela"onships
that
occur
in
natural
environments
-­‐
Our
approach
can
be
used
in
other
environments
/
situa<ons
where
discrete
and
con<nuous
tree
ring
series
are
available

20. BIENVILLE
MONTAUSIER
CORVETTE
LEC
NECOPASTIC
HERVÉ
POLARIS

21. Many
thanks
to
+
field
assistants
throughout
the
years
boucher@cerege.fr