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WG4: Flood frequency estimation methods and …

WG4: Flood frequency estimation methods and environmental changePublished by the Centre for Ecology & Hydrology on behalf of : 978-1-906698-36-2 Year of publication 2013 European Flood - frequency analysis in a changing environment iii Preface This report has been prepared as part of the COST Action ES0901 European procedures for Flood frequency estimation (FloodFreq) . The main objective of the FloodFreq COST Action is to undertake a Pan-European comparison and evaluation of methods for Flood frequency estimation under the various climatologic and geographic conditions found in Europe, and different levels of data availability.

European flood-frequency analysis in a changing environment v Summary The report presents a review of methods used in Europe for trend analysis, climate change

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Transcription of WG4: Flood frequency estimation methods and …

1 WG4: Flood frequency estimation methods and environmental changePublished by the Centre for Ecology & Hydrology on behalf of : 978-1-906698-36-2 Year of publication 2013 European Flood - frequency analysis in a changing environment iii Preface This report has been prepared as part of the COST Action ES0901 European procedures for Flood frequency estimation (FloodFreq) . The main objective of the FloodFreq COST Action is to undertake a Pan-European comparison and evaluation of methods for Flood frequency estimation under the various climatologic and geographic conditions found in Europe, and different levels of data availability.

2 The report has been prepared by Working Group 4 Flood frequency estimation methods and environmental change . It provides a review of methods used and results of detection of trends in observations and climate projections of extreme precipitation and Flood frequency in Europe. More information about the COST Action ES0901 can be found at the FloodFreq website European Flood - frequency analysis in a changing environment v Summary The report presents a review of methods used in Europe for trend analysis , climate change projections and non-stationary analysis of extreme precipitation and Flood frequency .

3 In addition, main findings of the analyses are presented, including a comparison of trend analysis results and climate change projections. Existing guidelines in Europe on design Flood and design rainfall estimation that incorporate climate change are reviewed. The report concludes with a discussion of research needs on non-stationary frequency analysis for considering the effects of climate change and inclusion in design guidelines. Trend analyses are reported for 21 countries in Europe with results for extreme precipitation, extreme streamflow or both.

4 A large number of national and regional trend studies have been carried out. Most studies are based on statistical methods applied to individual time series of extreme precipitation or extreme streamflow using the non-parametric Mann-Kendall trend test or regression analysis . Some studies have been reported that use field significance or regional consistency tests to analyse trends over larger areas. Some of the studies also include analysis of trend attribution. The studies reviewed indicate that there is some evidence of a general increase in extreme precipitation, whereas there are no clear indications of significant increasing trends at regional or national level of extreme streamflow.

5 For some smaller regions increases in extreme streamflow are reported. Several studies from regions dominated by snowmelt-induced peak flows report decreases in extreme streamflow and earlier spring snowmelt peak flows. climate change projections have been reported for 14 countries in Europe with results for extreme precipitation, extreme streamflow or both. The review shows various approaches for producing climate projections of extreme precipitation and Flood frequency based on alternative climate forcing scenarios, climate projections from available global and regional climate models, methods for statistical downscaling and bias correction, and alternative hydrological models.

6 A large number of the reported studies are based on an ensemble modelling approach that use several climate forcing scenarios and climate model projections in order to address the uncertainty on the projections of extreme precipitation and Flood frequency . Some studies also include alternative statistical downscaling and bias correction methods and hydrological modelling approaches. Most studies reviewed indicate an increase in extreme precipitation under a future climate , which is consistent with the observed trend of extreme precipitation.

7 Hydrological projections of peak flows and Flood frequency show both positive and negative changes. Large increases in peak flows are reported for some catchments with rainfall-dominated peak flows, whereas a general decrease in Flood magnitude and earlier spring floods are reported for catchments with snowmelt-dominated peak flows. The latter is consistent with the observed trends. The review of existing guidelines in Europe on design floods and design rainfalls shows that only few countries explicitly address climate change .

8 These design guidelines are based on climate change adjustment factors to be applied to current design estimates and may depend on design return period and projection horizon. The review indicates a gap between the need for considering climate change impacts in design and actual published guidelines that incorporate climate change in extreme precipitation and Flood frequency . Most of the studies reported are based on frequency analysis assuming stationary conditions in a certain time window (typically 30 years) representing current and future climate .

9 There is a need for developing more consistent non-stationary frequency analysis methods that can account for the transient nature of a changing climate European Flood - frequency analysis in a changing environment vii Editors Madsen, *, Lawrence, , Lang, , Martinkova, , Kjeldsen, *Corresponding author 1 DHI, H rsholm, Denmark 2 Norwegian Water Resources and Energy Directorate, Oslo, Norway 3 Irstea, UR HHLY, Lyon, France 4 T. G. Masaryk Water Research Institute, Prague, Czech Republic 5 Centre for Ecology & Hydrology, Wallingford, UK Contributors Willems, P.

10 , KU Leuven, Hydraulics Division, Leuven, Belgium Neykov, N., National Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences, Sofia, Bulgaria Balabanova, S., National Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences, Sofia, Bulgaria Toumazis, A., Dion Toumazis & Associates, Nicosia, Cyprus David, V., Faculty of Civil Engineering, Czech Technical University, Prague, Czech Republic Karsten Arnbjerg-Nielsen, DTU Environment, Technical University of Denmark, Denmark Veijalainen, N., Finnish Environment Institute, Freshwater Centre, Helsinki, Finland Renard, B.


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