unesco extreme meeting, paris, 27.-29.9.2010 g.c. leckebusch quantitative assessment of wind storms...
TRANSCRIPT
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Quantitative assessment of wind storms and extreme extra-tropical cyclones under climate
change
Gregor C. Leckebusch
Special Thanks to:
M. Donat, D. Renggli, T. Kruschke,
K. Nissen, P. Lorenz, T. Pardowitz, U. Ulbrich
Institute of Meteorology
Freie Universität Berlin, Germany
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
0) Outline
Introduction to extra-tropical cyclones
Gaussian and Lagrange Perspective of Cyclonic Activity
Recent climate conditions
Anthropogenic Climate Change
• Objective Wind Storm Identification • Extreme Value Analysis• Anthropogenic Climate Change
Summary
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
1. Introduction
Extra-tropical Cyclones: Crucial part of atmospheric circulation;Highly relevant for energy transports
Objective Measure of its strengths?How to deduce information about potential changes of these extreme events?Which processes influence the variability of cyclone occurrence?
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Cyclone & storm~Months ~Days
SST, NAO, snow
Growths factors for cyclones
latent heat Divergence
Baroclinicity
Adapted fromLutgens & Tarbuck (Eds., 2007) ECMWF Forecast for 20.05.2010 00 UTC
Geopotential 500 hPa
Potential Sources of Variability
~Decades
AMM, PNA, AMO, ENSO
~CentenialAnthropogenic Change
1. Introduction
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
MSLP: Stormtrack
Ulbrich et al., 2008 J. Climate
2. Gaussian Perspective
NCEP-NCAR, 1961-2000 23 AOGCM Ensemble
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Ulbrich, Pinto, Kupfer, Leckebusch, Spangehl, Reyers (2008), J Climate
1000 hPa Stormtrack: ACC-Signal (SRES A1B)
2. Gaussian Perspective
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
ERA40 Re-analysis: Track density Winter (ONDJFM), ALL Systems
Ensemble Mean: Track density Winter (ONDJFM), ALL Systems
Unit: Systems per winter
1961-2000
2. Lagrange Perspective: Cyclone Tracks
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
A1B Climate Change Signal All Systems
2. Lagrange Perspective: Cyclone Tracks
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Definition: Extreme Cyclone Systems
Systems with a Laplacian of MSLP ( )above the 95th percentile,
i.e. only the upper 5% of the distribution are recognised here
NCEP or ERA40 re-analysis: most of the historical relevant winter storms are included (as far as storms are resolved by re-analysis data)
2. Lagrange Perspective: Cyclone Tracks
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
A1B Climate Change Signal Strong Systems
Weighting via: W
Weight: W2
Weight: W4
For the region of e.g. NE Atlantic:ca. 10-20% increase
2. Lagrange Perspective: Cyclone Tracks
Leckebusch et al., 2008b
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Cyclone Intensity (Laplacian of MSLP) for ALL Systems:
2. Lagrange Perspective: Cyclone Tracks
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
European Storm Cyclones
ERA40, 1961-2000
Change Signal GCM-Ensemble
cyclone track density
intensity of storm cyclones
Max.Wind speed during storm days
(Donat, Leckebusch et al., 2010a)Isolines: Inter-model std.-dev
2. Lagrange Perspective: Cyclone Tracks
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Introduction of an objective Storm Severity Index (SSI) (cf. Leckebusch et al., 2008)
3
98
max, 1
)(
),(,0max
Ger
Ger
K
k
T
tkKT A
kv
tkvSSI
98th Percentile(ONDJFM)
m/s
Event Tracking: related to impacts
3. Wind storms: Identification
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
• Generalized Pareto Distribution
ξ : shapeσ : scaleμ : shift
Probability density function (pdf)
Containing 3 families of tail distributions• Rotated Weibull (with upper bound)
ξ < 0
• Gumbel (no bound, exponential decay of pdf) ξ = 0
• Fréchet (no upper bound, polynomial decay of pdf) ξ > 0
/1
1exp)(z
zG
e.g. Coles, An Introduction to Statistical Modeling of Extreme Values (2001)
)()( zGdz
dzg
3. Wind storms: 3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
All tracks are considered, which have at least one track point within the according region:
NORTH-EUROPE (NO-EU)
NORTH-WEST-EUROPE (NW-EU)
SOUTH-EUROPE (SO-EU)
NO
NW
SO
3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Threshold selection:
On average 1 event per year and model:= 1024 storms
SSI threshold: 11.19
Percentage of events from single model contribution to the ensemble
Extreme value analysis: Ensemble composition and threshold
%
SSI-Threshold
Region: NW-EU
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Total numbers of events in each 30 year periodENSEMBLESMulti-model ensemble inA1B scenario
Region: NW-EU
Model composition for each 30 year period
Events: SSI > 11.19
3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
2069-20981971-2000
Return Level of a 50-year EventRegion: NO-Europe
EVA:
stationary &non-stationary
model
ENSEMBLESMulti-model ensemble inA1B scenario
Region: NW-EU
3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Region RL5 RL10 RL25 RL50 RL100
NO-EUROPE
+53% +59% +67% +73% +79%
NW-EUROPE
+13% +14% +15% +15% +16%
SO-EUROPE
-19% -27% -36% -43% -49%
Relative changes of Return Levels by 2098 compared to 1971
Trends (non-stationary model)
Red: statistical significant on 95% level
3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
ECHAM5-OM1: 3x30 Years of 20C climate conditionsGermany !!!
3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
2011-2040
2041-2070
2071-2100
Results based on 3 x 30 year simulation (ECHAM5-OM1) SRES A1B scenarioRegion: Germany
3. Wind storms: EVA
UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch
Different methods to assess the potential anthropogenic changes in synoptic cyclone behaviour were applied or newly developed
Stormtrack: A 23 MME reveals significant increase at the downstream end of the climatological storm track over the North-Atlantic under ACC conditions
Cyclone tracks: ACC:
Reduction in the number of all cyclones on an hemispheric scale
Increase in frequency of severe cyclones in winter in certain “hotspots”, e.g. Northeast-Atlantic
Extreme Value Analysis identifies changes in the statistical properties of the frequency of severe wind storms
4. Summary