Transcript Proxies

Changes in storm occurrence
over Northern-Central Europe
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #1
Challenge
Storminess best represented by wind statistics, possibly
derived quantities such as stream function, vorticity, but
wind time series are almost always
• inhomogeneous
• too short
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Example of inhomogeneities
in wind records
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Losses from Atlantic
Hurricanes
The increase in damages
related to extreme
weather conditions is
massive – but is it because
the weather is getting
worse?
Hardly
“Great Miami”, 1926,
Florida, Alamaba – damages
of 2005 usage - in 2005
money: 139 b$
Katrina, 2005: 81 b$
Pielke, Jr., R.A., Gratz, J., Landsea, C.W.,
Collins, D., Saunders, M., and Musulin, R.,
2008. Normalized Hurricane Damages in
the United States: 1900-2005. Natural
Hazards Review
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #5
Wind, hydrology and
outlook
• For assessing ongoing change of the
occurrence of extremes as being
(partly) not within the range of
natural variations („detection“) and
for attributing most probable
causes to such changes
(„attribution“), we need
homogeneous descriptions of past
variability – for hundred and more
years, and projections of possible
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Two approaches:
proxies + downscaling
• Challenge
• Storminess best represented by wind
and precipitation short-term statistics
but such time series are almost always
• inhomogeneous
• too short
• For assessing changing storm
conditions, principally two approaches
are possible:
• Use of proxies, such as daily and subEuropean conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #7
Two approaches:
proxies + downscaling
• For assessing changing storm
conditions, principally two approaches
are possible:
a)Use of proxies, such a air pressure
readings.
b)Empirical or dynamial downscaling of
large scale information.
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #8
•Pressure
proxies
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Pressure based proxies
• Air pressure readings are usually
homogenous
• Annual/seasonal percentiles of
geostrophic wind derived from triangles
of pressure readings (e.g., 95 or 99%iles);
such percentiles of geostrophic wind and
of “real” wind are linearly related.
• Annual frequency of events with
geostrophic wind equal or larger than 25
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #10
Other storm proxies
• Variance of local water levels
relative to annual mean (high tide)
water level.
• Repair costs of dikes
in historical times.
• Sailing times of ships
on historical routes.
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•Proxies:
•N
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Geostropic wind stats N Europe
Relevant publications
99%iles of annual
geostrophic wind speeds
for a series of station
triangles in the North Sea
regions and in the Baltic
Sea region.
Alexandersson et al., 2002
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Local pressure stats since 1800
Stockholm
Relevant publications
Lund
Time series of pressure-based storminess indices derived from pressure readings in Lund (blue) and
Stockholm (red). From top to bottom: Annual number of pressure observations below 980 hPa (Np980),
annual number of absolute pressure differences exceeding 16 hPa/12 h (NDp/Dt),
Intra-annual 95-percentile and 99-percentile of the pressure differences (P95 and P99) in units of hPa.
From Bärring and von Storch, 2005: see also BACC 2008.
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #14
Regional
development of
Unchanging extratropcial
storminess and
storm conditions is not
contradicting the fact
that temerpature is
temperature
rising,
Lund and Stockholm
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•Proxies
•N + C
Matulla, C., W. Schöner, H. Alexandersson, H. von Storch, and X.L. Wang, 2007: European
Storminess: Late 19th Century to Present, Climate Dynamics DOI 10.1007/s00382-007-0333-y
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Proxies:
Geostrophic stats
normalized
21 year Gaussian filtered
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #17
24 hr pressure change stats
normalized
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Pressure Proxies E
Canada
less
Subarctic
more
Arctic
Change of intra-winter 10%-ile of pressure
readings at E Canadian stations Halifax and
Pondlnlet in the Arctic.
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #19
less
more
Applications: past and future
marine weather in N Europe
downscaling cascade for constructing
variable regional and local marine
weather statistics
Simulation with barotropic
model of North Sea
Globale development
(NCEP)
Dynamical Downscaling
REMO or CLM
Cooperation with a variety of governmental
agencies and with a number of private companies
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #20
Dynamical Downscaling: Baroclinic storms
Problem solved for synoptic systems in N Europe in
CoastDat@GKSS, using RCM spectrally nudged to NCEP
- retrospective analysis 1958-2005
- good skill with respect
to statistics, but not all
details are recovered.
Weisse, R., H. von Storch and F. Feser, 2005: Northeast Atlantic and North Sea storminess as
simulated by a regional climate model 1958-2001 and comparison with observations. J. Climate 18, 465479
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Stormcount 1958-2001
t≥T
Change of # Bft 8/year
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Weisse et al., J. Climate, 2005
t≤T
Dynamical Downscaling: Polar Lows
Continuous simulation
with regional model
CLM, 1948-2006, run
and (large-scale)
constrained with
NCEP/NCAR re-analysis
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #23
Dynamical Downscaling: E Asian Typhoons
60 year
simulation
with 50 km
grid,
Experimental
case and
season
simulations
with
embedded 18
km grid.
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E Asian tropical cyclones as given by
CLM downscaling
JMA best track data
40
30
20
10
0
1945
1950
1955
1960
1965
1970
1975
1980
Note: different criteria employed
1985
1990
1995
2000
2005
European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #25
2010
Conclusion: Usage
1. Monitoring extra-tropical
of proxies storminess
may be based on air pressure proxies.
2.This allows assessments for 100 and
more years.
3.Decades long upward and downwards
trends have been detected in recent
years.
4.These trends are not sustained and
have show recent reversals in all
considered regions.
5.Recent trends are not beyond the
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Conclusion:
Usage
of dynamical
1. Dynamical
downscaling
for describing
synoptic and downscaling
mesoscale variability is
doable.
2.Spectral nudging, or other forms of
large-scale constraint are helpful.
3.Simulation of extra-tropical baroclinic
disturbances satisfying; wind my be
used for simulating wave and surge
climatologies and trends.
4.Meso-scale variability (Polar Lows and
Tropical Cyclones) is also described, but
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