the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Nov 2025
The September 2024 Danube Flood Compared to the 1899, 2002, and 2013 Events: A Hydrometeorological Analysis in a Changing Climate
Abstract. In September 2024, an exceptional flood occurred in the Austrian Danube Basin, producing the highest discharges in parts of Lower Austria since instrumental records began. This study analyses the meteorological and hydrological drivers of the 2024 event and compares them with three historic floods with return periods of around 100 years at the Austrian Danube – 1899, 2002, and 2013 – to identify similarities, differences, and emerging trends in flood generation. Using representative station observations, reanalysis data, and hydrometric records from a dense network of river gauges, we examine atmospheric circulation, spatio-temporal rainfall patterns, runoff response, and flood-wave propagation along the Danube and its tributaries.
The 2024 flood was triggered by a quasi-stationary low-pressure system over the eastern Alps and western Hungary that produced two rainfall phases: a stratiform period in the west followed by convective extremes in the east, with local totals of 450–500 mm in five days. Although antecedent soil moisture was initially low, sustained rainfall led to rapid saturation and unusually high runoff coefficients (0.6–0.9) in central Lower Austria, where tributaries such as the Perschling and Kleine Tulln exceeded their HQ100 discharges by more than 150–250 %. In contrast, the main Danube and western Alpine tributaries showed only moderate responses.
The comparison with historical floods reveals a gradual shift from Alpine-controlled, basin-wide events toward regionally concentrated, convectively enhanced floods. The 2024 case highlights the increasing importance of atmospheric persistence, antecedent saturation, and tributary synchronisation in shaping flood extremes, providing new insights for adaptive flood-risk management in a changing climate.
Competing interests: Günter Blöschl is a member of the editorial board of HESS.
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.- Preprint
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Status: open (until 03 Jan 2026)
- RC1: 'Comment on egusphere-2025-5435', Anonymous Referee #1, 12 Dec 2025 reply
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RC2: 'Comment on egusphere-2025-5435', Anonymous Referee #2, 16 Dec 2025
reply
The study presented in this paper uses compares the September 2024 Danube flood to several historical floods in the same area and analyses the hydrometeorological conditions leading to the floods in the context of climate change.
The paper is well written and easy to follow, however, as I am no meteorologist I am not commenting on the meteorological part of the paper. Most of the comments are just minor corrections, and some to refer to the figures.
I recommend minor revisions and have listed some issues I found in the paper below.
Comments
- Please check the literature list as it does not seem to be complete. Lauda (1908) (page 2, line 54) is not in the literature list (however, this might be a typing mistake). Also, Godina et al. (2005) (page 2, line 59) and HD NÖ, 2024 (pages 15, line 287 and page 17, line 316) are not in the list. Merz et al. (2014) seems to be missing as well. There is a reference to Penna et al. (2006), which I could not find in the text. You might also want to check on the references to Blöschl et al. (2019) (page 29, line 502), Blöschl et al. (2020) (page 29, line 504), and Blöschl et al. (online 2019, printed 2020) (page 31, line 546), as there seems to be some kind of confusion.
- Line 71. Different word order suggested - Smaller tributary catchments in Lower Austria were hit particularly hard.
- Line 97. … to over 3000 m in the Alps. à … to over 3700 m in the Alps.
- Line 126-Line 136. Some parts of these lines seem to be redundant. Please revise.
- Line 140 (Figure 2) – is it possible to add the overlay of the Danube catchment as a red line? This would make orientation easier.
- Line 169 (Figure 3) – The figures do not have the same extent as Figure 2 – maybe this would be able to change. Adding an overlay of the Danube catchment as suggested before would help to orientate.
- Line 179. After Figure 4, there are two punctuation marks.
- Lines 200 ff. … roughly between St. Pölten and Vienna. You could add the two towns in Figures 4a-d for easier orientation. Also, the rivers Traisen and Perschling could be highlighted in the figures for the same reason.
- Line 217. The four maps how heavy rainfall… The word “show” seems to be missing.
- Line 222 (Figure 5) – add locations of some towns and rivers for easier orientation.
- Line 253 – Traisen-Pielach area – add location of rivers in Figure 7.
- Line 256 and 257. Admont and Mittersill – where are they?
- Lines 290 ff. Text is not consistent with Figure 8: … rainfall intensities in St. Pölten and Böheimkirchen. In Figure 8, Lilienfeld and St. Pölten are shown.
- Line 300. Figure 8. For the classification of the flood magnitude it could help to add some HQx (30, 100) values in the figure.
- Line 347 – At Korneuburg (not In Korneuburg)
- Lines 355 ff. … the Inn-Traun-Enns area produced only moderate discharges. In figure 11, the tributaries downstream between Linz and Melk seem to contribute a lot to the flood (steep increase!), also in Figure 9 the hydrographs in these catchments seem to contribute more runoff than the tributaries in Lower Austria.
- Line 368. The Lower Austrian tributaries supplied more than 1000 m³/s of additional discharge between Melk and Korneuburg. In the previous lines, the values for the Melk, Pielach, Ybbs, Traisen, Perschling and Große Tulln add up to roughly 3100 m³/s. Is this just because of the time lag in some of the catchments?
- Line 389. The 2024 maximum discharge of 9800 m³/s remained below the HQ30 level (9340 m³/s). Please check the numbers.
- Line 403. The contrast across the basinS is striking. Please add S at the end of basin.
Citation: https://doi.org/10.5194/egusphere-2025-5435-RC2 -
RC3: 'Comment on egusphere-2025-5435', Anonymous Referee #3, 21 Dec 2025
reply
The manuscript offers an interesting analysis of the recent extreme flooding in Austria in September 2024 and its classification in the context of previous historic flood events. The analysis considers the Danube catchment area above the gauge at Wildungsmauer and covers meteorological and hydrological aspects, including atmospheric conditions, precipitation characteristics, and the propagation of the flood wave. The study joins a series of analyses of previous events and provides new insights into the processes that lead to flooding in the Upper Danube region. The paper is well structured and well written. The results are presented in an appropriate way, and overall, I would recommend publication of the paper in HESS.
However, a few issues should be improved.
The statements about antecedent conditions in section 4.3 are mostly semi-quantitative, and it is not clear how these statements have been derived and if they are comparable between the different events. The paper would benefit from a more systematic assessment of antecedent catchment conditions
Section 5.1 provides an interesting spatial analysis of peak discharge frequency and runoff coefficients. However, this assessment is only shown for Austria and should be extended to the whole region of interest (Danube basin upstream of gauge Wildungsmauer). This analysis should also be applied to the historic events. Additional details about how runoff coefficients have been derived should be provided.
Other minor points that should be corrected are listed below.
l 55 Is the 2002 flood from the past century?
l 117 How is the 'estimated peak of the events' defined?
l 179 repeated full stop
l 180 How have the time periods for accumulated precipitation been determined for the different events?Fig. 4 upper Danube catchment is not completely covered, include lower Austria outline (yellow in Fig. 1)
l 204 rain persisted for five consecutive days - why are only 4 days shown in Fig. 5?
l 217 how - > show how
Fig. 5 indicate location of St. Pölten, Lilienfeld; include lower Austria outline (yellow in Fig. 1); legend title Niederschlag mm/Tag - > Precipitation mm/d
l 240 daily mean - > daily mean temperatures
l 256 Where are Admont and Mittersill located? Include location in Fig. 7
Fig. 7 Upper Danube catchment is not covered completely, include lower Austria outline (yellow in Fig. 1), include contour lines to give orientation for the snow lineFig. 9 Add the gauge station names to hydrographs; include lower Austria outline (yellow in Fig. 1)
l 341 not clear: Why is the 2024 flood steeper at Achleiten? It seems to be much lower and exhibits a double peak.
l 347 rephrase the sentence "By Korneuburg, the 2024 hydrograph closely approached that of 2013, indicating a shift from upstream-controlled to tributary-controlled flood dynamics." - what do you mean by closely? The 2024 flood peak is ca. 1000 m³/s below 2013 and shows a double peak, which is not discussed.
l 356 main-stem - > main-stream
ll 370-371 repetition from ll 348-349
l 387 stem -> stream
Fig 12: include historical reference event labels also for Boeheimkirchen and Sieghardskirchen plots
l 401 basin-wide indicators - > Fig 13 only covers Austria, should be expanded to Danube basin; include lower Austria outline (yellow in Fig. 1); (see above); Location of Perschling, Kleine Tulln, Traisen, and Pielach catchments should be indicated in the map
l410 and l413 Please provide ranges of typical runoff coefficients
l418 Flood peaks are only far above HQ100 in the tributaries, not in the Danube
Citation: https://doi.org/10.5194/egusphere-2025-5435-RC3
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- 1
The paper describes the Austrian flood(s) in September 2024, comparing it to previous notable events. The analysis is climatic, meteorological, and hydrological. The paper is structured as Blöschl et al. (2013), also published in HESS, which describes the August 2013 event in comparison to the previous ones. In a way, this paper is incremental in that a new event is added to the comparison. However, the climate change issue is tackled better in this last work, also thanks to other publications of the same group on the issue. The amount of information analysed here, the clarity of exposition, and the quality of the figures make the paper exemplary in terms of hydrometeorological characterisation of flood events.
Detailed comments:
- line 41: in Blöschl et al. (2020), the recent period is unprecedented in terms of being a flood-rich period in a warmer-than-usual climate. Blöschl et al. (2020) actually shows that other periods in the past were even more flood-rich than the recent one in Europe.
- line 66: what does “assess the plausibility” mean in this context?
- lines 135 and following: the description of the 2024 event here looks like a repetition of what was already said at lines 125 and following.
- line 143: “...during the peak of four historic flood events…”
- line 145: for non-meteorologists, maybe comment on how low the pressures are and how high is precipitable water compared to the usual.
- line 163: looking at Figure 3, Austria seems to be mostly covered by blue colour (negative anomaly). I do not see an abnormally warm air mass over Austria in the figure.
- line 217: The four maps show…
- Figure 5: Niederschlag to be translated.
- line 239: the cold-air outbreak seems consistent with Figure 3 colours (being that a high elevation temperature).
- Figure 7: the two panels seem to be one the negative of the other. Wouldn’t it be prettier to have both rain and snow on the same map but with different colours?
- Figure 8: why not showing more than one hydrograph here? Are the “local” hydrographs (those not affected by major confluences) similar, i.e., increasing slowly (because of the dry initial conditions) and decreasing quickly?
- Figure 9: maybe one could add an indication on how extreme the peak was for the individual sites (e.g. through the colours of the flood waves) to better show the relative importance of the eastern tributaries of the Danube to the event.
- Figure 10: I would mention the distance between the sites (or show them in Figure 9).
- line 370: are 4 events enough to detect the transition of flood dynamics? Is this transition something to be feared?
- Figure 11: if these sites were visible in Figure 9, that would help the reader.
- line 408: the patterns in the two panels of Figure 13 do not look that similar to me.
- line 410: does this imply that the other regions with high runoff coefficients, these are not that unusual?
- line 439: high runoff coefficients…
- line 446: shall we expect more synchronicity in neighbouring small-medium catchments only, or does the reasoning apply also to large catchments?