Permafrost temperatures at Schafberg

Permafrost temperatures at Schafberg
Evelyn Zenklusen Mutter, Juliette Blanchet, Marcia Phillips
[email protected]
CCES-Extremes Meeting, January 19-21, 2009
Outline
•
What is permafrost?
•
Motivation
•
Permafrost at Schafberg:
– Study site
– Ground temperature observation series
– Differences between two adjacent boreholes
– Temporal changes in ground temperature
– Extreme Values
•
Summary & future plans
Definition:
What is permafrost?
permafrost or permafrost soil
- soil at or below the freezing point
of water (0 °C) for two or more
years.
rock glaciers ~80% vol.
- ice is not always present, but it
frequently occurs
- most permafrost is located in high
latitudes, but alpine permafrost
may exist at high altitudes in much
lower latitudes.
cliffs 0 to ? %
Photos:
Marcia Phillips
detritus ~10%
Motivation
Photo: Markus Walser
thawing permafrost ...
- problems with buildings &
constructions (settlements,
liftings)
- natural hazards (rock slides,
debris flows, creeping
processes)
Photo: Marcia Phillips
Schafberg study site
Schafberg (2980 m ASL, Pontresina, E Swiss Alps)
Basel
Zürich
Bern
Davos
Schafberg
Genf
Lugano
Schafberg study site
B2
B1
Photo: Marcia Phillips
Ground temperature observation series
(4.10.1996- ...)
Borehole B1 (disturbed)
2.0 m
3.0 m
4.0 m
6.0 m
8.0 m
10.0 m
13.5 m
17.5 m
0.5 m
1.0 m
6
6
4
4
2
2
temperature [°C]
temperature [°C]
0.5 m
1.0 m
Borehole B2 (undisturbed)
0
-2
-4
-4
-6
-6
1.11.1998
1.11.2000
1.11.2002
1.11.2004
1.11.2006
4.0 m
6.0 m
8.0 m
10.0 m
0
-2
1.11.1996
2.0 m
3.0 m
1.11.1996
1.11.1998
1.11.2000
1.11.2002
1.11.2004
1.11.2006
13.5 m
17.5 m
Differences between B1 and B2
Mean monthly differences (B2-B1)
Near-surface layers
0.5m depth
°C
0.0 0.5 1.0
1.5
2.0
•
Jan Feb
Mrz
Apr
Mai
Jun
Jul
Aug
Sep
Okt
Nov Dez
Largest differences in late spring
and summer:
– B2 deeper active layer
(B2=~3m, B1=~1.5m)
– B1 longer persisting snow
cover
0.08
Deeper layers
0.04
•
0.00
°C
0.12
17.5m depth
Jan
Feb
Mrz
Apr Mai
Jun
Jul
Aug
Sep
Okt
Nov
Dez
Annual offset (B2 warmer than B1)
Conclusion 1
A longer persisting snow cover in summer (due to
avalanche defence structures) delays the penetration of
heat into the ground.
B2
B1
Ground temperature trends
Multiple regression with periodic function:
Y= ß0 + ß1*sin(2p T) + ß2*cos(2p T) + ß3*T + other terms + e
Ground temperature trends
Multiple regression with periodic function:
Y= ß0 + ß1*sin(2p T) + ß2*cos(2p T) + ß3*T + other terms + e
y-axis
intercept
periodic function with
corresponding frequency (1 year)
slope
sin+cos
sin+cos+trend
15
T: length of the period (expressed
in years)
e: error
exogenous explanatory
variables (0 in our model)
10
5
Trend: slope coefficient
significantly different from 0?
0
0
1000
2000
Index
3000
4000
Ground temperature trends
Trend [°C/yr]
Depth [m]
4.10.1996 – 9.7.2008
B1
B2
0.5 (s)
-0.03
-0.04
1.0 (s)
-0.02
-0.03
2.0 (s)
-0.01
-0.02
3.0 (s)
-0.01
-0.01
4.0 (s)
0
-0.09
6.0 (b)
0.01
0
8.0 (b)
0.01
0.01
10.0 (b)
0.02
0.01
13.5 (b)
0.03
0.02
17.5 (b)
0.03
0.03
... cooling inside the scree
... warming of the bedrock
Ground temperature trends
Warming
•
Global warming
•
Soil connected with atmosphere:
ground is warming too
Ground temperature trends
Ground temperature observations
B1 & B2: ~ 1997 - 2008
Ground temperature trends
Warming
Cooling
•
•
Global warming
How does it fit into the global
warming story?
Important!
•
Soil connected with atmosphere:
ground is warming too
•
Tground = f(Tair, topography,
ground cover)
•
Ground cover: vegetation,
scree, bedrock, snow, ..
à snow ...
changing over the last years?
Ground temperature trends
snow cover and ground temperatures
Rules:
snow gauge B1
snow gauge B2
Concerning the interaction between
snow & ground temperature
400
•
Thick snow cover = insulator:
decouples ground from atmosphere
•
Thin snow cover = high albedo +
low insulation: strong cooling effect
•
Time of occurrence
– Thin snow cover at early winter
⇒ cooling effect on permafrost
– Thick snow cover at early
winter ⇒ insulating effect on
permafrost
snow depth [cm]
300
200
100
0
01.01.1996
01.11.1998
01.11.2001
01.11.2004
01.11.2007
Ground temperature trends
snow cover and ground temperatures
cycle 1999
cycle 2003
01.11.1998 – 31.10.1999
01.11.2002 – 31.10.2003
150
200
250
300
11
12
1
2
3
4
5
6
7
8
9
10
100
snow depth [cm]
200
150
100
0
50
50
0
snow depth [cm]
250
300
11
12
1
2
3
4
5
6
7
8
9
10
-6
-4
-2
ground temperature [°C]
0
2
-6
-4
-2
ground temperature [°C]
0
2
Ground temperature trends
snow cover and ground temperatures
Has the snow regime changed over the last years?
•
Number of days
a) with snow cover
b) with snow cover > certain depth (~1m)
c) a) & b) in different seasons (early winter, late winter, high winter, melting
season, summer)
•
Mean snow depth (monthly, seasonally)
•
Air temperatures of the corresponding seasons/months
Problem: missing data (several days/weeks successively) ...
•
Limits to calculate monthly means
•
Snow interpolation with neighbour station („extreme“ location)?
•
Further ideas ...?
... Maybe conclusion 2
In the last years the development of a thick insulating snow
cover occurred later so winterly cooling of the ground
could happen more efficiently.
Trend [°C/yr]
Depth [m]
4.10.1996 – 9.7.2008
B1
B2
0.5 (s)
-0.03
-0.04
1.0 (s)
-0.02
-0.03
2.0 (s)
-0.01
-0.02
3.0 (s)
-0.01
-0.01
4.0 (s)
0
-0.09
6.0 (b)
0.01
0
...
...
...
Ground temperature trends
first speculations
Ground temperature trends
first speculations
? warming rock walls
à positive ground temperature trends in depth
Ground temperature trends
? Ventilation
? increased
winterly cooling
à Cooling inside
the scree
first speculations
? warming rock walls
à positive ground temperature trends in depth
Extreme values
(only Schafberg B1 will be shown)
Extreme values
classification into cold and warm months
Visual classification for every depth (0.5m – 10.0m):
2
depth 0.5m
-2
-4
warm months
-6
°C
0
cold months
1101
1201
101
201
301
401
501
601
701
801
901
1001
1031
Extreme values
GEV parameter estimates
__
warm months
__
cold months
Extreme values
return levels
__
warm months
__
cold months
Extreme values
trend in location parameter
• likelihood ratio test (1%) è trend in location parameter
• annual increase/decrease is similar to earlier results calculated
by annual maxima/minima
Depth [m]
Trend location parameter warm
months [°C/yr]
Trend location parameter cold
months [°C/yr]
0.5
0.034 *
0.062
1.0
0.016 *
0.034
2.0
0.023 *
0.025
3.0
0.022 *
0.010
4.0
0.028 *
0.002
6.0
0.036 *
-0.009
8.0
0.042 *
-0.015
10.0
0.041 *
-0.020 *
Conclusion 3
Annual summer maxima in ground temperature seem to
increase.
Summary & further steps
Ground temperature observations inside the permafrost of Schafberg
lead to the following
Conclusions:
1.
Longer persisting snow cover (due to avalanche defence structures) attenuates
summer warming of the ground.
2.
Response time to warm air temperature is delayed by the coarse and blocky
debris layer of the scree slope which has a cooling effect on the ground.
3.
Annual summer maxima in ground temperature seem to increase.
Further steps:
•
Further analysis of snow covered / snow free periods
•
Modelling of the heat transfer through Schafberg ridge
•
Further process study of cooling scree slope
Thank you for your attention!
Questions ..?
"International Snow Science Workshop 2009 Davos, 27 Sept – 2 Oct 2009
www. issw.ch” + Workshop Construction in Permafrost!
Additional explanatory slides
Schafberg: active layer depth
Def.:
maximum annual active layer depth (ALD)
= the maximum annual penetration of the 0° isotherm (Burn, 1998)
•
max annual ALD in B2 almost as
twice as thick as in B1 (local
differences in stratigraphy, hydrology
and solar radiation, Rist and Phillips
2005)
•
Slight increase of max annual ALD in
B1 and B2
•
Temporary strong deepening during
the extremely hot summer 2003
•
Annual duration of the active layer:
sig. Positive trends 1997-2007 in both
boreholes: B2 +5d/yr, B1 + 6d/yr
Reaction to seasonal warming/cooling
surface
Procedure:
•
year xy
0.5m
Compare the
occurrence of the
annual
minimum/maximum
temperatures at certain
depths
13.5 m
•
No annual cycle below
a certain depth
25.02.
depth
03.08.
time
Schafberg:
reaction time to seasonal cooling
Cooling in winter ...
a)
b)
Depending on snow cover thickness at the beginning of the winter
B1 and B2 react similarly
B1 annual Tmin
B2 annual Tmin
Schafberg
reaction time to seasonal warming
Warming in summer ...
a)
a)
Delayed within the uppermost 3-4 metres due to the presence of the insulating
snow cover
Can additionally be delayed by 1-2 months at B1 compared to B2 (avalanche
defence structures)
B1 annual Tmax
B2 annual Tmax
Ground temperature trends
first speculations
North
•
Gemsstock:
– narrow ridge
– 40m borehole across the
ridge
– Southern slope warmer
than northern slope
– Summer warmth
penetrates into the rock
•
Schafberg:
– Cross section through
Schafberg ridge (~80m)
– Try to model heat fluxes
South
warming effect
Ground temperature trends
first speculations
Winterly Cooling
Ventilation
Conclusion 2:
seasonal chimney effect inside coarse
blocky scree slopes
recent years: thin snow cover at the
beginning of the winter à strong
winterly cooling of the ground
Known phenomenon:
Delaloye, R., and Lambiel, C. 2005.
Fact:
scree has an insulating effect in
summer (high air content)
Consequence:
Phillips M., Zenklusen Mutter E.,
Kern-Luetschg M., and Lehning M.
(in press)
Consequence:
cooling effect