Joint Trends in Flood Magnitudes and Spatial Extents Across Europe

Kemter, Matthias; Merz, Bruno; Marwan, Norbert; Vorogushyn, Sergiy; Blöschl, Günter

doi:10.1029/2020gl087464

Cited by 102 publications

(108 citation statements)

References 31 publications

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“…The important role of both meteorological and land-surface processes in shaping spatial flood dependence suggests the potential for substantial change in the spatial dependence (and even overall occurrence) of floods in a warming climate. Kemter et al (2020) have shown in a recent study that spatial flood extents are already undergoing changes because of changes in the importance of different flood generating mechanisms. In future, the spatial dependence of floods may evolve in a spatially and temporally nonuniform manner due to changes in snowmelt contributions to runoff (Li et al, 2017), the frequency of rain-on-snow events (Li et al, 2019), the spatial extent of convective storms (Chang et al, 2016;Wasko et al, 2016), widespread projected soil moisture aridification (Cook et al, 2015), and shifting regional seasonality of precipitation (Swain et al, 2018).…”

Section: Implications For Changes In Spatial Flood Dependence In Warmmentioning

confidence: 99%

“…Two recent studies by Berghuijs et al (2019) and Kemter et al (2020) have shown for large sets of European catchments that the distance between catchments experiencing floods at the same time varies regionally and depends on the homogeneity of a particular region's flood generating mechanisms. While the authors looked at regional differences in this distance, seasonal differences were not considered because their analysis focused on annual maxima floods.…”

Section: Introductionmentioning

confidence: 99%

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Spatial Dependence of Floods Shaped by Spatiotemporal Variations in Meteorological and Land‐Surface Processes

Brunner

Gilleland

Wood

et al. 2020

Geophysical Research Letters

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Floods often affect large regions and cause adverse societal impacts. Regional flood hazard and risk assessments therefore require a realistic representation of spatial flood dependencies to avoid the overestimation or underestimation of risk. However, it is not yet well understood how spatial flood dependence, that is, the degree of co‐occurrence of floods at different locations, varies in space and time and which processes influence the strength of this dependence. We identify regions in the United States with seasonally similar flood behavior and analyze processes governing spatial dependence. We find that spatial flood dependence varies regionally and seasonally and is generally strongest in winter and spring and weakest in summer and fall. Moreover, we find that land‐surface processes are crucial in shaping the spatiotemporal characteristics of flood events. We conclude that the regional and seasonal variations in spatial flood dependencies must be considered when conducting current and future flood risk assessments.

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Section: Implications For Changes In Spatial Flood Dependence In Warmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spatial Dependence of Floods Shaped by Spatiotemporal Variations in Meteorological and Land‐Surface Processes

Brunner

Gilleland

Wood

et al. 2020

Geophysical Research Letters

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“…Please note that Figure 3 is not a representation of changes in flood-rich/poor periods but a representation of the total number of flood-rich/poor periods, which is a reflection of the degree of temporal clustering of floods. On the other hand, the regional differences in the frequencies (e.g., much larger frequency in central eastern than Atlantic) may be more related to differences in the flood generating mechanisms such as a prevalence of snowmelt floods in eastern Europe (Kemter et al, 2020). Figures A1 and A2 give the corresponding maps for 2-and 10-year thresholds, and the percentages of the anomalies are 17.54% and 12.31%, respectively.…”

Section: 1029/2019wr026575mentioning

confidence: 99%

Detecting Flood‐Rich and Flood‐Poor Periods in Annual Peak Discharges Across Europe

Lun

Fischer

Viglione

et al. 2020

Water Resources Research

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This paper proposes a method from Scan statistics for identifying flood‐rich and flood‐poor periods (i.e., anomalies) in flood discharge records. Exceedances of quantiles with 2‐, 5‐, and 10‐year return periods are used to identify periods with unusually many (or few) threshold exceedances with respect to the reference condition of independent and identically distributed random variables. For the case of flood‐rich periods, multiple window lengths are used in the identification process. The method is applied to 2,201 annual flood peak series in Europe between 1960 and 2010. Results indicate evidence for the existence of flood‐rich and flood‐poor periods, as about 2 to 3 times more anomalies are detected than what would be expected by chance. The frequency of the anomalies tends to decrease with an increasing threshold return period which is consistent with previous studies, but this may be partly related to the method and the record length of about 50 years. In the northwest of Europe, the frequency of stations with flood‐rich periods tends to increase over time and the frequency of stations with flood‐poor periods tends to decrease. In the east and south of Europe, the opposite is the case. There appears to exist a turning point around 1970 when the frequencies of anomalies start to change most clearly. This turning point occurs at the same time as a turning point of the North Atlantic Oscillation index. The method is also suitable for peak‐over‐threshold series and can be generalized to higher dimensions, such as space and space‐time.

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“…These works fueled debates on the origins and hence the choice of appropriate methods for estimating upper tail (i.e., the largest) floods. Moreover, recent process‐based investigations of flood changes (e.g., Berghuijs et al, 2019; Blöschl et al, 2019; Kemter et al, 2020) showed that their observed disparate regional patterns might in fact be driven by changes in the mix of flood generation processes, thus further complicating reliable estimations of future flood hazards.…”

Section: Introductionmentioning

confidence: 99%

Transformation of Generation Processes From Small Runoff Events to Large Floods

Tarasova

Basso

Merz

2020

Geophysical Research Letters

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Mixture of runoff generation processes poses a challenge for predicting upper flood quantiles. We examined transformations of generation processes from all identifiable runoff events to frequent and upper tail floods for a large set of mesoscale catchments and observed a substantial change of the dominant processes. Two trajectories of transformation were detected. In regions where floods occur almost exclusively in winter the dominance of processes related to snowmelt consistently increases from small events to frequent and upper tail floods. In catchments characterized by frequent winter-spring floods and occasional summer-autumn flood events triggered by rare meteorological phenomena (e.g., Vb cyclones), processes that dominate upper tails are not adequately represented in the sample of frequent floods. Predictions of extremes and projections of flood changes might remain highly uncertain in the latter cases. Plain Language Summary Prediction of floods remains a challenging task for the engineering practice. Floods triggered by different physical mechanisms have contrasting statistical attributes. Mixture of these processes hinders reliable prediction of the largest floods. In this study we classified a large number of streamflow events observed in a wide range of German river basins according to their generation processes. We analyzed changes in the frequency of occurrence of different generation processes, from the smallest identifiable runoff events to annual floods to rarer events corresponding to larger river flows. Interestingly, for some river basins certain processes tend to consistently increase their frequency from small streamflow events to common and larger floods. In other cases, we observed an opposite tendency. Certain processes become less important for the generation of annual floods compared to small streamflow events but then dominate generation of the largest floods. This has important implications for our ability to predict extreme floods and their possible changes.

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Joint Trends in Flood Magnitudes and Spatial Extents Across Europe

Cited by 102 publications

References 31 publications

Spatial Dependence of Floods Shaped by Spatiotemporal Variations in Meteorological and Land‐Surface Processes

Spatial Dependence of Floods Shaped by Spatiotemporal Variations in Meteorological and Land‐Surface Processes

Detecting Flood‐Rich and Flood‐Poor Periods in Annual Peak Discharges Across Europe

Transformation of Generation Processes From Small Runoff Events to Large Floods

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