the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Brief communication: A first hydrological investigation of extreme August 2023 floods in Slovenia, Europe
Panos Panagos
Leonidas Liakos
Matjaž Mikoš
Abstract. Extreme floods occurred from 4th to 6th of August 2023 in Slovenia claiming 3 casualties and causing economic damage of a few billions EUR. The weather situation not typical for summer period in combination with high temperatures of the Mediterranean Sea and high antecedent soil moisture lead to the most extreme flood event in the last several decades. The return period of precipitation extremes and peak discharges exceeded 250–500 years return period, and runoff coefficient of typical torrential and mostly forested meso-scale catchments was around 0.5. Additionally, intense soil erosion, mass movements and sediment transport processes caused large damages on housing and infrastructure.
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Nejc Bezak et al.
Status: open (until 27 Oct 2023)
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RC1: 'Comment on egusphere-2023-1979', Anonymous Referee #1, 11 Sep 2023
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This is a well elaborated paper on a recent disaster event of Slovenian floods occuring at the beginning of August this year. Although submittted only a month after the event, it already presents some important insights. Having said that, there are some issues (mainly in presentation of the research) that should be addressed in order to improve comprehensibility and impact of the paper.
- the duration of the event could be reconsidered for consistency throughout the manuscript. Abstract indicates August 4-6, but as far as I know, heavy rains started in the evening of August 3 already causing local floods (which seems to be indicated in the paper as well)
- l. 17 - please provide more specific explanation or a reference to what do you mean by 'unstable terrain'
- l. 20 - relation of the extremes to climate change continues to be a subbject of studies and discussions. Authors should provide regionally-specific references to these links.
- Figure 1 - I sugget adding a scale into the photos since they are not easy to read
- l. 49 - authors describe the synoptic situation leading to heavy rains and floods. I believe this is a very important part of the manuscript and should be extended and possibly illustrated with a synoptic/pressure field map. Also, when talking about future trends (l. 131) and increasing probabilities of similar flood events, authors could not only point to temperature or rainfall trends, but provide a comment on whether the specific synoptic situation is becoming more frequent
- l. 96 - authors mention flooded areas according to satellite maps, but it is not clear who did this estimation. If it was another organisation, it should be specified. If it was the authors, than I think it is redundant and they should only present their final (up-to-date) estimates. Also figures (satellite images) in supplement would have benefitted from inserted arrows or numbers that would refer to specific morphological changes. Currently, it is up to readers' ability to analyse the images.
- l. 126-7 - the sentence about implications of increased rainfall needs rephhrasing or clarification
- there is also a couple of typos (not affecting general readability) and the paper should b checked again for language consistency
- authors may consider avoiding the term 'natural disaster', which has been widely problematised recently
Citation: https://doi.org/10.5194/egusphere-2023-1979-RC1 -
CC1: 'Comment on egusphere-2023-1979', Lorenzo Marchi, 12 Sep 2023
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The amount and quality of data on the flood of August 4-6, 2023 in Slovenia gathered and processed by Bezak and colleagues deserves to be stressed. Such data collection and analysis is especially remarkable as it was implemented a few weeks after the event, thus timely providing the scientific community with fundamental data on flood drivers, runoff response, and produced damage.
This short comment proposes a comparison of unit (or specific) peak discharge observed in the August 2023 flood with a severe flash flood that occurred in Slovenia on September 18, 2007. The September 2007 flood was caused by a shorter-duration rainstorm and affected a much smaller area, mostly corresponding to the catchment of Selška Sora, west of the sector most severely affected by the August 2023 flood.
It can be observed (Fig. 1) that the empirical threshold line of unit peak discharge (Qu) versus catchment area (A) derived for the 2023 flood (Qu=28·A-045) fits well also the highest values of the 2007 flood. Data from the 2007 flood mostly derive from post-flood surveys in ungauged channels (Marchi et al., 2009). The fact that another remarkable flood is defined by the same upper limit of unit peak discharge could increase the significance of this envelope line for the design of mitigation measures.
It can also be noted that the threshold line that defines the upper limit of the August 2023 (and September 2007) floods lies below not only global envelopes such as those by Herschy (2002) but also the regional envelope for Alpine and Alpine-Mediterranean catchments (Amponsah et al., 2018).
Fig. 1. Comparison of the empirical envelope curve for the August 2023 flood with data from the September 2007 flood and the regional envelope curve for Alpine and Alpine-Mediterranean catchments (Amponsah et al., 2018).
References
Amponsah, W., Ayral, P.-A., Boudevillain, B., Bouvier, C., Braud, I., Brunet, P., Delrieu, G., Didon-Lescot, J.-F., Gaume, E., Lebouc, L., Marchi, L., Marra, F., Morin, E., Nord, G., Payrastre, O., Zoccatelli, D., Borga, M.: Integrated high-resolution dataset of high-intensity European and Mediterranean flash floods. Earth Syst. Sci. Data, 10, 1783–1794, https://doi.org/10.5194/essd-10-1783-2018, 2018
Herschy, R. W.: The world’s maximum observed floods, Flow Meas. Instrum., 13(5), 231–235, https://doi.org/10.1016/S0955-5986(02)00054-7, 2002
Marchi, L., Borga, M., Preciso, E., Sangati, M., Gaume, E., Bain, V., Delrieu, G., Bonnifait, L., Pogačnik, N.: Comprehensive post-event survey of a flash flood in Western Slovenia: observation strategy and lessons learned. Hydrological Processes, 23(26), 3761-3770, https://doi.org/10.1002/hyp.7542, 2009
Citation: https://doi.org/10.5194/egusphere-2023-1979-CC1 -
CC2: 'Comment on egusphere-2023-1979', Ognjen Bonacci, 18 Sep 2023
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I think that this paper is very important. As , it is brief communication it can be accepted as it is.
Citation: https://doi.org/10.5194/egusphere-2023-1979-CC2
Nejc Bezak et al.
Nejc Bezak et al.
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