Southern Germany's 100-year flash flood discharge expected to increase by 30 % under an RCP8.5 climate

Voit, Paul; Hundhausen, Marie; Seregina, Larisa; Feldmann, Hendrik; Ahrens, Bodo; Heistermann, Maik

doi:10.5194/egusphere-2026-1229

Preprints

https://doi.org/10.5194/egusphere-2026-1229

Preprints

08 Apr 2026

| 08 Apr 2026

Status: this preprint is open for discussion and under review for Natural Hazards and Earth System Sciences (NHESS).

Southern Germany's 100-year flash flood discharge expected to increase by 30 % under an RCP8.5 climate

Paul Voit, Marie Hundhausen, Larisa Seregina, Hendrik Feldmann, Bodo Ahrens, and Maik Heistermann

Abstract. The frequency and intensity of convective heavy rainfall events are generally assumed to increase in a warming climate. So far, however, it remained difficult to assess the corresponding changes in flash floods. This difficulty resulted from the mismatch between the coarse spatial resolution of global and regional circulation models, which do not explicitly resolve convective processes, and the small spatial extent of flash-flood-prone headwater catchments. Recently, though, the results of several convection-permitting climate models (CPMs) became available for parts of Germany. Our study presents the first attempt to utilize these high-resolution data (1 h, 3 km) for an assessment of flash-flood changes in southern Germany. Based on an ensemble of 6 CPM models, we simulated the runoff for the periods 1971–2000 (historical) and 2071–2100 under the RCP8.5 scenario for the German part of the Danube basin. We then compared the 100-year return levels of rainfall and discharge maxima between these two periods. The results indicate an increase of 100-yr flood return levels for 94 % of the Danube subcatchments with a median increase of 30 % across all subcatchments under the RCP8.5 scenario.

Received: 05 Mar 2026 – Discussion started: 08 Apr 2026

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Preprint (PDF, 1724 KB)

Supplement (3659 KB)

Download & links

Paul Voit, Marie Hundhausen, Larisa Seregina, Hendrik Feldmann, Bodo Ahrens, and Maik Heistermann

Status: open (until 02 Jul 2026)

Post a comment Subscribe to comment alert

RC1:
'Comment on egusphere-2026-1229', Alison Kay, 14 May 2026 reply
Review of “Southern Germany’s 100-year flash flood discharge expected to increase by 30% under an RCP8.5 climate” by Voit et al.
This is an interesting and well-written paper using data from multiple CPMs with a flash-flood model to investigate potential future changes in such floods across southern Germany. The higher spatial and temporal resolution of data from CPMs are clearly going to be important for flood modelling, at least for some events/catchments (see for example my own recent work using hourly 5km CPM precipitation data for Britain https://onlinelibrary.wiley.com/doi/10.1002/hyp.70523).
I only have relatively minor comments:
My main issue is that I don’t really like the term ‘flash-flood’ as I feel it is ill-defined in the literature generally. Can you be precise about what you mean by this term, and are you sure that all the events you are analysing fit that definition?

It is stated in Section 2.2, and shown in Fig 1, that one of the CPMs does not include the whole drainage area. How does this affect modelling of downstream catchments - surely it means some water-input to these catchments is missing? This should be discussed.

In Section 3.2 it says that the modelling is limited to March-October, because you focus on convective rainfall and have no snow routine. But how are antecedent conditions then properly accounted for, if you don’t run the model continuously? By antecedent conditions I mainly mean soil moisture, but also is there no snowpack still to melt at the start of March in some places in this region? Can ‘flash floods’ sometimes be caused by rapid snowmelt and/or rain-on-snow, and how might this change in future?

Section 2 says that the flash-flood model has been ‘proven and tested’ previously. A brief outline of what this actually means would be helpful. E.g. presumably this has used observed driving data and compared against observed flows, but where, over what range of catchments/events, how were you judging performance?

In Section 3.3, it’s rather confusing to describe extracting annual maxima if you are only modelling Mar-Oct…

Also in Section 3.3, you say that basins where the shape parameter is outside a certain range are excluded, but the number excluded varies by CPM. This means that an inconsistent number of catchments is used for various later plots. Is there a sub-set of catchments that are well-behaved for all CPMs, which could be used subsequently?

Section 4.2: I like the pooling of annual maxima from all ensemble members – since you are looking at 100-year return period events this larger sample will be helpful (although the question is whether this could skew results in a certain direction based on members of the ensemble, since it’s an ensemble of opportunity rather designed for this purpose). Can you make it clear that ‘fitting to pooled AM’ is what you mean for the bottom plot in Fig. 2 (i.e. it’s not just taking all the points from the above 6 plots and plotting boxplots for the larger set)?

Adding a horizontal line at 1 for the plots in Fig 2 would help, since this represents the boundary between increases or decreases.

You could also note that the pooled data might be better used with the empirical distribution rather than fitted EVD, although this might be more the case with initial-condition climate ensembles than the multi-model ensemble you have here (e.g. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL081967).

Line 182: what do you mean by ‘significantly though not substantially’?!

Line 189: ‘ensure’ or ‘guarantee’.

Line 194: I’m confused by the ‘results not shown’ comment. The reduced spread of ratios is in the bottom plot in Fig 2, compared to plots above? Or do you mean that you have checked the robustness of GEV fits. If the latter, could you add this info in the Supp Mat?

Alison Kay, UKCEH, May 2026

Reply
Citation: https://doi.org/10.5194/egusphere-2026-1229-RC1

Paul Voit, Marie Hundhausen, Larisa Seregina, Hendrik Feldmann, Bodo Ahrens, and Maik Heistermann

Supplement

https://doi.org/10.5194/egusphere-2026-1229-supplement

Paul Voit, Marie Hundhausen, Larisa Seregina, Hendrik Feldmann, Bodo Ahrens, and Maik Heistermann

Viewed

Total article views: 501 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	Supplement	BibTeX	EndNote
354	123	24	501	54	20	20

HTML: 354
PDF: 123
XML: 24
Total: 501
Supplement: 54
BibTeX: 20
EndNote: 20

Views and downloads (calculated since 08 Apr 2026)

Month	HTML	PDF	XML	Total
Apr 2026	218	92	13	323
May 2026	120	29	8	157
Jun 2026	16	2	3	21

Cumulative views and downloads (calculated since 08 Apr 2026)

Month	HTML	PDF	XML	Total
Apr 2026	218	92	13	323
May 2026	120	29	8	157
Jun 2026	16	2	3	21

Viewed (geographical distribution)

Total article views: 499 (including HTML, PDF, and XML) Thereof 499 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 08 Jun 2026

Short summary

Extreme rainfall is expected to increase with a warming climate. However, it remains unclear how this will impact future floods. This study utilizes an ensemble of 6 new datasets, containing the future projected rainfall, and compares the simulated flash floods of the past (1971–2000) and future (2071–2100) under the RCP8.5 scenario for the German part of the Danube catchment. Our results indicate an increase of 100-yr flood return levels of 30 % across all subcatchments under this scenario.


Total:	0
HTML:	0
PDF:	0
XML:	0