ENVIRONMENTAL CHANGES IN THE SOUTHERN CANADIAN
ROCKIES FROM MULTIPLE TREE-RING PROXIES
Emma Watson1, Brian Luckman2, Greg Pederson3 and Rob Wilson4
1Meteorological
Service of Canada, Environment Canada
of Geography, University of Western Ontario
3U.S. Geological Survey and Big Sky Institute, Montana State University
4School of Geosciences, Edinburgh University
2Department
Peyto Glacier in 1966 taken by W.E.S. Henoch (NHRI Canadian Glacier Information Centre).
Introduction
• study of glacier fluctuations had traditionally provided many of
our ideas about the climate history of the last millennium in the
Canadian Rockies
• Paleoclimate signal in glacier records is complex, incomplete and
biased to large events
• we describe tree-ring based research of the late Holocene climate
of the area
• in particular we detail the development of continuous records of
temperature, precipitation, glacier mass balance and streamflow
from tree-ring chronologies sampled in different environments
which can be compared with the glacial record
PEYTO
Moraine dating is
available from 66
glacier forefields
in the Canadian
Rockies
Luckman, 2000
Summary of Little Ice Age (LIA) glacier events in the Canadian Rockies
Periods of advance:
• 1150-1350 (advances through forest- calendar dated logs)
• selected preservation of glacier record between 14th and 17th centuries
• widespread advances early 18th and throughout 19th century
May-August Maximum temperatures Columbia Icefield, Canadian Rockies 950-1995
Based on regional ringwidth and maximum tree-ring density chronologies
Update to Luckman (1997) using: more chronologies from wider area (i.e. better replication
and more regionally representative); different predictand (original Apr-Aug mean) and RCS
standardization of MXD data
• RCS on average cooler,
shows more low
frequency trend, 1690s
most extreme cold period
reconstructed
Anomalies from 1901-1980 mean
Comparison with northern Hemisphere temperature reconstructions
Standardized to the 1000-1980 period.
Tree ring chronologies and precipitation records
Instrumental and estimated precipitation
Smoothed annual precipitation reconstructions
for the southern Canadian Cordillera
Widespread wet periods
Widespread dry periods
Using tree-rings to study glacier mass balance
• mass balance is a time series that represents the difference
between accumulation and ablation on a glacier on an annual
basis - mass balance records are short (~30 yrs)
• because tree-ring chronologies are responsive to similar climate
controls as those that influence mass balance, they may be useful
for studying and reconstructing mass balance
• Developing seasonal mass balance reconstructions can help us
understand the climate parameters responsible for changes in
glacier length (e.g. do the contributions of winter and summer
balance vary back through time or during important intervals (e.g.
the LIA max?)
Peyto Glacier, Rocky Mountains, Alberta
Peyto Glacier in 1966 taken by W.E.S. Henoch
(NHRI - Canadian Glacier Information Centre).
Area estimates
• Outlet glacier from Wapta Icefield
• contributes flow to the Mistaya River
catchment and the North Saskatechewan
River Basin
1887 17.15 km2
Peyto Glacier in 1966 taken by W.E.S. Henoch
(NHRI - Canadian Glacier Information
Centre).
2
1966 13.5 km
1993 11.81 km2
• 34% decrease in Bw
Impact of 1976 PDO shift on glacier mass balance in the Pacific Northwest
Relationships between measured mass balance and instrumental climate (1966-1995)
• meteorological data from stations in Banff, Jasper, Lake Louise, Golden, Carway, Valemont
• agrees with other findings for continental glaciers (e.g. Yarnal, 1984)
Winter balance (Bw) – October-April precip
Summer balance (Bs) – June-Aug temps
500
Banff temperature
Banff precipitation
450
17
300
13
250
200
11
150
100
y = -0.0009x + 11.18 9
y = 0.1296x + 93.774
50
0
0
500
1000
1500
R = 0.70
R = -0.48
R2 = 0.49
R 2 = 0.23
2000
2500
-3000
-2500
-2000
-1500
-1000
-500
7
0
Bs (mwe)
Bw (mwe)
18
350
Jasper precipitation
Jasper temperature
17
300
Oct-April precip (mm)
mean Jun-Aug tmp ( oC)
15
350
16
250
15
200
14
150
13
100
12
50
y = 4.8817x + 256.81
y = -0.0014x + 11.723
R = 0.65
R = -0.83
R = 0.61
R = 0.42
0
0
500
1000
1500
Bw (mwe)
2000
11
2
2
2500
-3000
-2500
-2000
-1500
Bs (mwe)
-1000
-500
10
0
mean Jun-Aug tmp ( oC)
Oct-April precip (mm)
400
Reconstruction Strategy
• goal = reconstruct seasonal and net mass balance from tree-ring chronologies
• ablation related to SUMMER temperatures therefore use summer temperature reconstruction
• winter accumulation more difficult because there are no winter-sensitive chronologies available for
the area
• winter climate in Alaska and the southern Canadian Cordillera are both influenced by conditions in
the North Pacific
Typical winter season climate anomalies during positive PDO years
• therefore, use tree-ring chronologies from Alaska to study WINTER mass balance at Peyto
Location and length of records used in the study
Lat. N
Monthly Climate Records
Banff Precipitation1
51 11
1
Banff Temperature
51 11
Jasper Precipitation1
52 53
2
Jasper Temperature
52 53
Long. W
Elev. (m)
Prov./State
Length
115 34
115 34
118 04
118 04
1389
1389
1061
1061
Alb.
Alb.
Alb.
Alb.
1895-1995
1895-2001
1936-1995
1916-1994
Mass Balance
Peyto3
51 41
116 32
2140-3180
Alb.
1966-1997
Tree-Ring Data
Miners Well (MW)4
Athabasca (ATHA)5
Waterton (WA)6
Lytton (LY)6
60 00
52 13
49 28
50 14
141 41
117 14
113 34
121 35
650
2000
1200
258
Alaska
Alb.
Alb.
B.C.
1428-1995
869-1994
1673-1996
1468-1996
Reconstructed versus measured mass balance at Peyto Glacier
The predicted net mass balance
series is the difference between the
winter and summer series
It is not a separate reconstruction.
Mass balance reconstructions
(1673-1994) for Peyto Glacier
based on tree-ring data
• 1966-1995 winter accumulation below
long-term mean
• 1966-1995 summer ablation is greater
than the long-term mean
• 1966-1995 net mass balance is well
below the long-term mean
• the LIA maximum at Peyto glacier is
estimated between ca. 1836 and 1841
based on dating of killed and damaged
trees along the western trimline
(Luckman, 1996)
mean balances
1673-1883 +70 mm w.e./yr.
1883-1993 -317 mm w.e./yr.
• the decrease in Bn since the 1880s
corresponds well with Wallace’s (1995)
estimate that Peyto has lost 70% of its
volume over the past 100 years
Moving correlations between the seasonal and net mass balance series
Correlations calculated using a 31-year window (plotted on central year). The dashed horizontal
lines denote statistical significance (p<0.05). Correlations over the full period (1673-1994) are
given in parenthesis beside each legend entry.
• over the full period correlations are highest between Bn and Bs
• Bn-Bw and Bn-Bs correlations are variable but always significant
• Bw-Bs are not significantly correlated over the full period but correlate positively during the early
1700s and 1800s (higher accumulation and reduced ablation) and again near the end of the record
(lower accumulation and greater ablation)
The LIA moraine record for the Canadian Rockies and
reconstructed mass balance at Peyto Glacier
Dated moraines in the Canadian Rockies
(66 glaciers, 25 year intervals Luckman
2000)
• The reconstructed periods of
positive mass balance during the
early 18th, early and late 19th centuries
immediately precede or coincide with
regional periods of moraine
development in the Canadian
Rockies.
•The correspondence between these
totally independent proxy climate
records provides strong mutual
verification of the regional climate
history.
• some glaciers in the Premier range
built small moraines in the 1970s
(Luckman et al., 1997)
Exploring relationships with Pacific SSTs
• winter mass balance reconstruction filtered to yield time series of high (<8 years) and low (>8 years)
frequency variability
• Nov-Mar SSTs regressed on the mass-balance reconstructions (1870-1994)
previous studies have associated changes in glacier mass balance with decadal-Interdecadal
variability in the Pacific Ocean
• the mass balance reconstructions allow relationships with SSTs to be explored over a much longer
period than the short measured balance records (1966-present) permit
Winter balance – high frequency
ENSO-like pattern
Winter balance – low frequency
Resembles pattern of decadal-interdecadeal
variability identified previously (e.g. Zhang et al. 1997)
• Luckman (2000) noted that at the
most northerly sites (Mount Robson
area and Premier Ranges), most
glaciers have 18th century moraines at
their downvalley limits while few
glaciers farther south formed moraines
during this period (e.g. Kananaskis
area)
• only 19th century moraines have been
identified in Waterton Lakes National
Park and Glacier National Park,
Montana
1300 1400 1500 1600
1700 1800 1900
Mass Balance reconstructions in the Canadian and northern U.S. Rockies
• How do recent mass balance
reconstructions for Peyto Glacier and
Glacier National Park, Montana compare?
Does the timing of the LIA maximum
coincide?
Mass Balance reconstructions for Peyto Glacier and Glacier National Park (GNP)
For a detailed comparison of these mass balance records please see the poster by
G. Pederson, E. Watson, B. Luckman, D. Fagre, S. Gray and L. Graumlich titled:
Tree-Ring Based Estimates of Glacier Mass Balance in the Northern Rocky
Mountains for the Past 300 Years
Exploring the controls of pre-instrumental streamflow
How have changes in precipitation (winter and summer) and glacier wastage affected
streamflow?
Can this be addressed using tree-ring based reconstructions?
Bow at Banff streamflow (1912-1996)
• flows from Bow glacier in Wapta Icefield
across the semi-arid Canadian Prairies
• unregulated upstream
Banff precipitation
• precipitation-sensitive Douglas-fir
chronologies exist and have been used to
reconstruct annual (July-June precipitation)
Data used in this study
Peyto Glacier Mass balance
• outlet glacier from Wapta Icefield
• regionally representative
• separate summer and winter balances
available which represent summer melting
and winter accumulation (i.e. snowpack)
What controls streamflow?
Correlations with climate-related
parameters over the instrumental
period
• does not correlate highly with summer
precipitation
•streamflow correlates most highly with
winter precipitation at Banff (r=0.68)
• Bw correlates with winter precipitation at
Banff (r = 0.60) and Bow streamflow and
can therefore be used as a surrogate
for winter snowpack
•flow is snowmelt dominated
• 76% of flow is concentrated in the
months April-August
Instrumental
Bow Apr-Aug
Common period (1966-19941)
Instrumental
Banff Pre (Apr-Aug)
Banff Pre (Oct-Apr)
Peyto Bw
Peyto Bs
0.15
0.68
0.60
0.09
Developing a physically realistic streamflow reconstruction for the Bow at Banff
• Decided to model summer flow
• Predictors = precipitation-sensitive chronologies from Cranbrook, Jasper and Waterton AND winter
Balance (as a surrogate for winter snowfall)
Summary characteristics of the reconstruction
Reconstruction Record/Season
Length 1
Bow at Banff
1619-1995 4 1912-1995 0.60
streamflow/Apr-Aug
N
calib.
period
calib.
R
calib.
Adj. R2
ver.
r2
2 SE
%of mean
0.33
0.29
25
Summer precipitation reconstruction for Banff
• April-August based on Douglas-fir chronology from Banff
• totally independent of streamflow reconstruction
Summary characteristics of the reconstruction
Reconstruction Record/Season
Length 1 N
Banff
1308-1995 2 1896-1994 0.60
precipitation/Apr-Aug
calib. calib.
period
R
calib.
Adj. R2
ver.
r2
2 SE
%of mean
0.35
0.31
43
How realistic is the streamflow
reconstruction?
• instrumental streamflow correlates most
highly with winter precipitation at Banff
(r=0.68; 1966-1994) and this relationship is
also identified in the reconstructed series.
Reconstructed
Bow Apr-Aug
Common period (1966-1994)
Reconstructed
Banff Pre (Apr-Aug)
Peyto Bw
Peyto Bs
0.24
0.53
0.11
Maximum Paired Interval (1912-1996)
Reconstructed
Banff Pre (Apr-Aug)
Peyto Bw
Peyto Bs
0.28
0.41
0.01
Simple comparison of reconstructions
Winter precipitation (snowpack)
Summer melting
Summer precipitation
Summer streamflow
• difficult to establish to what
extent coherent departures
are a result of causal
relationships or pure
coincidence
• However, the majority of
low and high streamflow
events over past 350 years
are related to changes in
snowpack (33%) or
snowpack and summer
precipitation (44%)
• remaining 23% of
pronounced high and low
streamflow events appear to
be related to changes in
summer precipitation alone
Moving correlations between streamflow and inputs
• Relationships between the variables vary considerably through time
• Correlations between streamflow and summer balance (glacier melting) over the
full period of record are not significant (p>0.05) -- small component of total flow; outside the seasonal
window; proportion of flow in individual months related to glacier wastage varies by year.
• suggests that total volume of flow may not change as much as the timing of flow and that such
changes in timing cannot be detecting using these tree-ring data
Conclusion
• Tree-ring chronologies from different species and environments can
be used to reconstruct temperature and precipitation and more
complex variables such as glacier mass balance and streamflow in
the Canadian Rockies
• Intercomparison of independently-derived proxy records from within
and outside the region are useful for validating results and identifying
the spatial scales of climate events (e.g. droughts)
• Future attempts to integrate and compare reconstructions must try
to reconcile differences in the climate signal in the proxies and the
timing of changes in the environmental variable of interest
• A better understanding of the relationships between glacier mass
balance, streamflow and the major driving forces of climate variability
(e.g. ENSO, PDO etc ) will be useful in predicting how these
phenomena may respond to future climate changes.