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

Transcription

1 COST733 Final workshop Classifications in atmospheric sciences and their applications, present state & future directions. Vienna, Austria November 2010 Application of a weather type classification to assess the impact of climate change on flood occurrence in Austria Philipp Stanzel 1, Thomas Krennert 2, Hans-Peter Nachtnebel 1 1 Institute of Water Management, Hydrology and Hydraulic Engineering Department of Water, Atmosphere and Environment University of Natural Resources and Life Sciences, Vienna, Austria 2 ZAMG-Central Institute for Meteorology and Geodynamics, Vienna, Austria

2 Floods Large floods in Austria 2002, 2005 (picture: Steyr 2009) more floods due to climate change

3 Floods Large floods in Austria 2002, 2005 (picture: Steyr 2009) more floods due to climate change Flood trends in Austria, Nobilis&Lorenz 1997 no general trends observed Flood trends in Germany, Petrow&Merz 2009

4 Method Aim: Investigate possible changes in occurrence of flood events due to climate change in Austria Using climate model data Focusing on meteorological impacts Approach: Periods of flood occurrence 20C (runoff observations) (ERA40) (GCM control runs) Flood generating weather types weather types 21C (GCM scenario) Flood occurrence 21C

5 Method Aim: Investigate possible changes in occurrence of flood events due to climate change in Austria Using climate model data Focusing on meteorological impacts Approach: Periods of flood occurrence 20C (runoff observations) (ERA40) (GCM control runs) Flood generating weather types weather types 21C (GCM scenario) Flood occurrence 21C

6 Weather type classification Simplified version of the WLKC733 classification scheme developed in the framework of COST Input variables: geopotential height at 500 hpa and 925 hpa true wind at 700 hpa Result: 36 weather types described by flow direction class cyclonic or anticyclonic vorticity at the two levels D Weather type example: 7 A C 7 : wind dominantly from west A: anticyclonal at 500hPa C: cyclonal at 925hPa 15X 2X 1X wind sectors (0 = undefined) domain of analysis and weights

7 Flood periods Runoff data: 554 gauges Seven climate regions in Austria Peak over threshold approach (4 events/year) Seasonal analysis Month with highest flood frequency Month with highest flood frequency

8 Flood generating weather types Flood generating period: day of peak + 2 days before Weather type catalogue for from ERA40 Relative frequency of occurrence of weather types in flood generating periods (relative to overall occurrence) hhw WL = = i dhw i= d WL WL rel.freq. during flood periods weather type:

9 Flood generating weather types climate region 5 - Donau - winter (DJF) 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 weather type 0AC 0AA 8CA 0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16 rel. frequency of occurence in flood generating periods climate region 7 - Mühl-Waldviertel - spring (MAM) 7AC weather type 3CC 6AC 0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16 rel. frequency of occurence in flood generating periods

10 Method Aim: Investigate possible changes in occurrence of flood events due to climate change in Austria Using climate model data Focusing on meteorological impacts Approach: Periods of flood occurrence 20C (runoff observations) (ERA40) (GCM control runs) Flood generating weather types weather types 21C (GCM scenario) Flood occurrence 21C

11 Climate model data and WLK733 relative frequencies 30% 25% 20% 15% 10% 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 5% shifts from control runs to scenarios (2 nd half of 21 st century) smaller than deviations 20C ERA40 20C ECHAM5 A1B ECHAM5 B1 ECHAM5 20C HADCM3C A1B HADCM3C weather type weather type 20C ECHAM5 20C HADCM3C 20C ERA40 (observation) 8CA 0AC 0AA 0,00 0,02 0,04 0,06 0,08 0,10 0,12 relative frequencies of occurence in 20 th century 20C ECHAM5 20C HADCM3C 20C ERA40 (observation) 3CC 7AC 6AC 0,00 0,02 0,04 0,06 0,08 0,10 0,12 relative frequencies of occurence in 20 th century 0% flow direction classes

12 Method Aim: Investigate possible changes in occurrence of flood events due to climate change in Austria Using climate model data Focusing on meteorological impacts Approach: Periods of flood occurrence 20C (runoff observations) (ERA40) (GCM control runs) Flood generating weather types weather types 21C (GCM scenario) Flood occurrence 21C

13 Climate change and flood occurence Change in occurrence of flood generating weather typ: Indicator for change in flood occurence Qualitative analysis 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 8CA 0AC HADCM3C A1B 0AA -0,10-0,05 0,00 0,05 0,10 0,15 0,20 change in weather type frequency * rel. frequ. of occurence before floods 3CC 6AC HADCM3C A1B 7AC -0,10-0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 change in weather type frequency * rel. frequ. of occurence before floods 8CA 0AC ECHAM5 A1B 0AA -0,10-0,05 0,00 0,05 0,10 0,15 0,20 change in weather type frequency * rel. frequ. of occurence before floods 7AC 3CC 6AC ECHAM5 A1B -0,10-0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 change in weather type frequency * rel. frequ. of occurence before floods 8CA 0AC 0AA ECHAM5 B1-0,10-0,05 0,00 0,05 0,10 0,15 0,20 change in weather type frequency * rel. frequ. of occurence before floods 3CC 6AC 7AC ECHAM5 B1-0,10-0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 change in weather type frequency * rel. frequ. of occurence before floods

14 Conclusions 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.

15 COST733 Final workshop Classifications in atmospheric sciences and their applications, present state & future directions. Vienna, Austria November 2010 Thank you for your attention! Philipp Stanzel Thomas Krennert Hans-Peter Nachtnebel The presented work was funded by the Austrian Klima- und Energiefonds