Preprints
https://doi.org/10.5194/hess-2021-628
https://doi.org/10.5194/hess-2021-628
 
21 Dec 2021
21 Dec 2021
Status: this preprint is currently under review for the journal HESS.

More frequent flash flood events and extreme precipitation favouring atmospheric conditions in temperate regions of Europe

Judith Meyer1,2, Malte Neuper3, Luca Mathias4, Erwin Zehe3, and Laurent Pfister1,2 Judith Meyer et al.
  • 1Catchment and Ecohydrology Group (CAT), Environmental Research and Innovation, Luxembourg Institute of Science and Technology (LIST), Belvaux, 4422, Luxembourg
  • 2Faculty of Science, Technology and Medicine (FSTM), University of Luxembourg, Esch-sur-Alzette, 4365, Luxembourg
  • 3Institute of Water Resources and River Basin Management, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 4Air Navigation Administration, MeteoLux, Findel, Luxembourg

Abstract. In recent years, flash floods repeatedly occurred in temperate regions of central western Europe. Unlike in Mediterranean catchments, this flooding behaviour is unusual. In the past, and especially in the 1990s, floods were characterized by predictable, slowly rising water levels during winter and driven by westerly atmospheric fluxes (Pfister et al., 2004). The intention of this study is to link the recent occurrence of flash floods in central western Europe to extreme precipitation and specific atmospheric conditions to identify the cause for this apparent shift. Therefore, we hypothesise that an increase in extreme precipitation events has subsequently led to an increase in the occurrence of flash flood events in central western Europe and all that being caused by a change in the occurrence of flash flood favouring atmospheric conditions. To test this hypothesis, we compiled data on flash floods in central western Europe and selected precipitation events above 40 mm h−1 from radar data (RADOLAN, DWD). Moreover, we identified proxy parameters representative for flash flood favouring atmospheric conditions from the ERA5 reanalysis dataset. High specific humidity in the lower troposphere (q ≥ 0.004 kg kg−1), sufficient latent instability (CAPE ≥ 100 J kg−1) and weak deep-layer wind shear (DLS ≤ 10 m s−1) proved to be characteristic for long-lasting intense rainfall that can potentially trigger flash floods. These atmospheric parameters, as well as the flash flood and precipitation events were then analysed using linear models. Thereby we found significant increases in atmospheric moisture contents and increases in atmospheric instability. Parameters representing the motion and organisation of convective systems occurred slightly more often or remained unchanged in the time period from 1981–2020. Moreover, a trend in the occurrence of flash floods was confirmed. The number of precipitation events, their maximum 5-minute intensities as well as their hourly sums were however characterized by large inter-annual variations and no trends could be identified between 2002–2020. This study therefore shows that the link from atmospheric conditions via precipitation to flash floods cannot be traced down in an isolated way. The complexity of interactions is likely higher and future analyses should include other potentially relevant factors such as intra-annual precipitation patterns or catchment specific parameters.

Judith Meyer et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-628', Anonymous Referee #1, 09 Jan 2022
  • RC2: 'Comment on hess-2021-628', Ruben Imhoff, 10 Jan 2022
  • RC3: 'Comment on hess-2021-628', Anonymous Referee #3, 18 Jan 2022

Judith Meyer et al.

Judith Meyer et al.

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Short summary
We showed that flash floods occurred more often in recent years in central western Europe. Therefore, we identified and analysed the major atmospheric ingredients for rain-intense thunderstorms: high atmospheric moisture, sufficient latent instability, and weak thunderstorm cell motion. Between 1981–2020, atmospheric conditions became likelier to support strong thunderstorms. The occurrence of extreme rainfall events, as well as their rainfall intensity, stayed, however, mostly unchanged.