application of a weather type classification to assess … of a weather type classification to...

Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria

Philipp Stanzel1, Thomas Krennert2, Hans-Peter Nachtnebel1

1Institute of Water Management, Hydrology and Hydraulic EngineeringDepartment of Water, Atmosphere and Environment

University of Natural Resources and Life Sciences, Vienna, Austria

2ZAMG-Central Institute for Meteorology and Geodynamics, Vienna, Austria

COST733 Final workshopClassifications in atmospheric sciences and their applications, present state & future directions.

Vienna, Austria22-24. November 2010


Large floods in Austria2002, 2005(picture: Steyr 2009)

“more floods due to climate change”

Floods


Large floods in Austria2002, 2005(picture: Steyr 2009)

“more floods due to climate change”

no general trends observed

Floods

Flood trends in Austria, Nobilis&Lorenz 1997

Flood trends in Germany, Petrow&Merz 2009


− Aim: Investigate possible changes in occurrence of flood events due to climate change in Austria

• Using climate model data

• Focusing on meteorological impacts

− Approach:

Method

Periods of flood occurrence 20C(runoff observations)

Catalogue of weather types 20C

(ERA40)

Flood generating weather types


(GCM control runs)


(GCM scenario)

Flood occurrence 21C


− Simplified version of the WLKC733 classification scheme developed in the framework of COST733

− Input variables: • geopotential height at 500 hPa and 925 hPa

• true wind at 700 hPa

− Result: 36 weather typesdescribed by

• flow direction class

•cyclonic or anticyclonic vorticity at the two levels

Weather type classification

1

3

45

6

7

8 2

15X 2X1X

D06

• wind sectors (0 = undefined)• domain of analysis and weights

Weather type example: 7 A C

7 : wind dominantly from west

A: anticyclonal at 500hPa

C: cyclonal at 925hPa


Month with highest flood frequency

1

234

5

6

7

Flood periods

− Runoff data:• 554 gauges• 1971 - 2000

− Seven climate regions in Austria

− Peak over threshold approach (4 events/year)

− Seasonal analysis

Month with highest flood frequency



− Flood generating period: day of peak + 2 days before

− Weather type catalogue for 1971-2000 from ERA40

− Relative frequency of occurrence of weather types in flood generating periods (relative to overall occurrence)

∑∑

=

==

di

dHWiWL WL

WLhhw

rel.freq. during flood periods

weather type: 1AA



Weather types with high relative frequencies in flood periods identified

10 flood generating weather types selected for CC analysis

for each climate region and season

6AC

7CC

8AC

8CC

3CC

7CA

7AA

8AA

1AA

7AC

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16rel. frequency of occurence in flood generating periods

wea

ther

ty

pe

climate region 7 - Mühl-Waldviertel - spring (MAM)

0AA

0AC

7CC

8CC

1AA

8AC

7AA

8CA

7CA

8AA

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16rel. frequency of occurence in flood generating periods

wea

ther

ty

pe

climate region 5 - Donau - winter (DJF)





− Approach:

Method



(ERA40)



(GCM control runs)


(GCM scenario)



− Climate model data:

• ECHAM5 : A1B, B1

• HADCM3C: A1B

−WLK733: ERA40 vs. GCM control runs• good agreement for flow directions

• large discrepancies for specific weather types

−WLK733: scenarios• shifts from control runs to scenarios (2nd half of 21st century) smaller than deviations

Climate model data and WLK733

0%

5%

10%

15%

20%

25%

30%

0 1 2 3 4 5 6 7 8

rela

tive

frequ

enci

es

flow direction classes

20C ERA40

20C ECHAM5

A1B ECHAM5

B1 ECHAM5

20C HADCM3C

A1B HADCM3C

0AA

0AC

7CC

8CC

1AA

8AC

7AA

8CA

7CA

8AA

0,00 0,02 0,04 0,06 0,08 0,10 0,12relative frequencies of occurence in 20th century

wea

ther

ty

pe

20C ECHAM5 20C HADCM3C 20C ERA40 (observation)

6AC

7CC

8AC

8CC

3CC

7CA

7AA

8AA

1AA

7AC

0,00 0,02 0,04 0,06 0,08 0,10 0,12relative frequencies of occurence in 20th century

wea

ther

ty

pe

20C ECHAM5 20C HADCM3C 20C ERA40 (observation)





− Approach:

Method



(ERA40)



(GCM control runs)


(GCM scenario)



− Change in occurrence of flood generating weather typ:

Indicator for change in flood occurence

− Qualitative analysis

Climate change and flood occurence

0AA

0AC

7CC

8CC

1AA

8AC

7AA

8CA

7CA

8AA

-0,10 -0,05 0,00 0,05 0,10 0,15 0,20change in weather type frequency *rel. frequ. of occurence before floods

HADCM3C A1B

0AA

0AC

7CC

8CC

1AA

8AC

7AA

8CA

7CA

8AA


ECHAM5 A1B

0AA

0AC

7CC

8CC

1AA

8AC

7AA

8CA

7CA

8AA


ECHAM5 B1

6AC

7CC

8AC

8CC

3CC

7CA

7AA

8AA

1AA

7AC

-0,10 -0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35change in weather type frequency *rel. frequ. of occurence before floods

HADCM3C A1B

6AC

7CC

8AC

8CC

3CC

7CA

7AA

8AA

1AA

7AC


ECHAM5 A1B

6AC

7CC

8AC

8CC

3CC

7CA

7AA

8AA

1AA

7AC


ECHAM5 B1

For most climate regions and seasons projected changes varied for different climate models and scenarios

Consistent findings only for winter and spring and western and northern regions: increase in frequencies of flood generating weather types


Flood generating weather types can be identified with WLKC733

Large uncertainties in climate change application:

• Discrepancies in weather type frequencies from reanalyses and GCM control runs

• Different projections in different scenarios and different models

No drastic changes in circulation patterns over central Europe expected

Consistent trends:

• Increase in north-western and western flows in winter and spring

• Indicator for more frequent flood occurrences in northern and western regions of Austria, where these circulation patterns prevalently cause flood events.

Conclusions


Philipp Stanzel ([email protected])Thomas KrennertHans-Peter Nachtnebel

The presented work was funded by the Austrian “Klima- und Energiefonds”

Thank you for your attention!

COST733 Final workshopClassifications in atmospheric sciences and their applications, present state & future directions.

Vienna, Austria22-24. November 2010

application of a weather type classification to assess … of a weather type classification to...

Documents