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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
Large floods in Austria2002, 2005(picture: Steyr 2009)
“more floods due to climate change”
Floods
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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
Catalogue of weather types 20C
(GCM control runs)
Catalogue of weather types 21C
(GCM scenario)
Flood occurrence 21C
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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
Catalogue of weather types 20C
(GCM control runs)
Catalogue of weather types 21C
(GCM scenario)
Flood occurrence 21C
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
Flood generating weather types
− 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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
Flood generating weather types
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)
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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
Catalogue of weather types 20C
(GCM control runs)
Catalogue of weather types 21C
(GCM scenario)
Flood occurrence 21C
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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)
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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
Catalogue of weather types 20C
(GCM control runs)
Catalogue of weather types 21C
(GCM scenario)
Flood occurrence 21C
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
− 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
-0,10 -0,05 0,00 0,05 0,10 0,15 0,20change in weather type frequency *rel. frequ. of occurence before floods
ECHAM5 A1B
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
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
-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
ECHAM5 A1B
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
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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
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
Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria
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