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Federal Departement of Home Affairs FDHAFederal Office of Meteorology and Climatology MeteoSwiss
Revisiting Swiss temperature trends 1959-2008*
Paulo Ceppi, Simon C. Scherrer, Andreas M. Fischer, Christof Appenzeller
Federal of Office of Meteorology and Climatology MeteoSwiss
16 July 201011th International Meeting on Statistical Climatology, Edinburgh UK
* submitted to the International Journal of Climatology
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2 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
MotivationTemperature trends: The hallmark of climate change
IPCC 2007, WG1
seasonal differences different processes on different spatial scales
local climate change = large scale + local processes
new Swiss grid
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3 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Outline
Geographical setting, input data and gridding
What are the linear temperature trends (yearly / seasonal)?
Can regional climate models explain the observed trends?
What is the trend contribution of
… large scale circulation?
… local factors?
Conclusions
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4 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Geographical setting and input data
91 homogeneous station series, 1959-2008 station altitude range: 203 to 3580 m asl ~2 km x 2 km gridded data set
Edinburgh
Switzerland
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5 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Monthly anomaly griddingclimatological distance λ
spatial interpolation of altitude corrected residuals influence of topography determined independently every month
C. Frei, MeteoSwiss
valley setting
λ = 0.01 λ = 0.05 λ = 0.1
summit setting
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6 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Gridded temperature anomaliesExample December 2009
good representation of local/altitude effects!
C. Frei, MeteoSwiss
topography
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7 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Yearly temperature trends1959-2008 (°C/10yrs)
average OLS trend: +0.35°C/10yrs
stronger trends than in global mean (+0.13°C/10yrs)
highly significant trends everywhere (p < 0.0005)
small spatial variability
no altitude dependence
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8 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Seasonal temperature trends1959-2008 (°C/10yrs)
°C/10yrs trends positive, (almost) everywhere significant
large seasonal differences of the trends [°C/10yrs] autumn weak (+0.02-0.38), summer strong (+0.34-0.62)
clearly larger than NH-land (exception autumn)
altitude depences in autumn (stronger for low altitudes)
NH-land
trend [°C/10yrs]
dens
ity
SONJJA
MAM
DJF
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9 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Can climate models reproduce warming?Northern Switzerland
ENSEMBLES models (smoothed)
observed change (smoothed)
ano
mal
y [°
C]
wrt
196
1-19
90
20yr Gaussian smoothing
but: models are NOT forced with observed circulation! Can observed circulation changes explain the differences?
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10 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
)(tTOBS = + )(tε)(tTCIRC
Different warming by circulation changes? Linear regression model
Quantify effect of circulationon T via regression model:
• principal components (PCs) of geopotential height at 500 hPa over N-Atlantic/Europe
• model calibration: 1959-83 / validation: 1984-2008• choice of PCs by „stepwise selection“
observed temperatures
“modell error”other effects
)(10
1
tPCi
ii∑=
β
atmospheric circulation
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11 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Circulation effects on temperatureSwiss mean 1959-2008
trend lines 1959-2008observed / modelled trend (°C/10yrs)
observed / modelled temperatures
bright: calibration dark: validation
0.35 0.13
0.39 0.21
0.46 0.07
0.39 0.08
0.17 0.02
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12 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Summary temperature trend analysisSwitzerland 1959-2008
[°C/10yrs]DJF MAM JJA SON YEAR
observed 0.40 0.39 0.46 0.17 0.35
circulation 0.21 (54%) 0.08 (21%) 0.07 (15%) 0.02 (12%) 0.13 (37%)
residual 0.19 0.31 0.39 0.15 0.22
Can regional climate models account for the residual (circulation corrected) trends?
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13 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Summary temperature trend analysisSwitzerland 1959-2008
[°C/10yrs]DJF MAM JJA SON YEAR
observed 0.40 0.39 0.46 0.17 0.35
circulation 0.21 (54%) 0.08 (21%) 0.07 (15%) 0.02 (12%) 0.13 (37%)
residual 0.19 0.31 0.39 0.15 0.22
RCM 0.16 0.18 0.16 0.24 0.18
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14 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
trend (°C/10yrs)
Altitude dependencegridded temperature trends 1959-2008
negative
anomaly
°C/10yrs
altitude [m
asl]
positive
anomaly
0.6
0.4
0.2
0
-0.2
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15 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Swiss temperature trend anomalies1959-2008 [°C/10yrs] month-to-month evolution
altitude [m
asl]
month of the year
more trend than all altitude average
less trend than all altitude average
3000
2500
2000
1500
1000
500
Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
changes in fog/visibility?
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16 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Swiss temperature trend anomalies1959-2008 [°C/10yrs] incl. mean temperature evolution [°C]
altitude [m
asl]
month of the year
more trend than all altitude average
less trend than all altitude average
3000
2500
2000
1500
1000
500
Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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17 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
altitude [m
asl]
month of the year
Swiss temperature trend anomalies1959-2008 [°C/10yrs] … and mean snow pack [cm]
more trend than all altitude average
less trend than all altitude average
100
30
5
100
30
5
snow-albedo effect?3000
2500
2000
1500
1000
500
Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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18 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh [email protected]
Conclusions
Swiss temperature trends stronger than NH-land trend (1.6)
Large seasonal differences, altitude dependence in autumn
~50% of the trend in winter due to changes in circulation – much less in other seasons
Regional climate models underestimate circulation corrected trends in spring & summer
Local processes important for local trends, especially in autumn (fog), spring (snow-albedo effect) and summer