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