In this study, the Authors investigate the principal factors that influence the spatiotemporal variability and frequency of extremes of Suspended Sediment Load (SSL) in the Alps; please see some minor and one major issue that I hope they can be of help to the Authors:

1) Please mention in the Abstract the hierarchy of the identified impacts of “the catchment elevation, the start of the melt season, and the presence of glaciers.”.

2) I think the main conclusion that “The analysis of 2,398 extreme SSC events across all catchments indicates that rainfall is the primary driver of SSC extremes, responsible for 80% of all events.” may be expected. Please link this to the literature regarding existing SSC hydrological models that also use rainfall as the primary impact force. Also, please mention in the Abstract and Conclusions about the rest of 20% that rainfall was not identified as the primary factor of SSC events and please give further details on the primary factors and how can these be physically justified.

3) The Authors use the SSC units “g/L”. I think for all the SSL events, and their impacts to the environment and humans, to can be directly compared, the SSL material should be similar; is the SSL material similar in all the examined catchments/rivers in the Alps, and if not, maybe it could be useful to mention the differences in the SSLs.

4) Regarding soil-moisture and streamflows, did the Authors considered land-use changes during these 10 years of data that could have an impact to both these processes and so, to the measured SSL?

5) The Authors use 10 years of observed sub-daily SSL data from 38 gauging stations in Switzerland and Austria, and they consider “time-varying hydro-climatic processes and forcing”; I am concerned that 10 years of data may not be sufficient for the investigation of spatio-temporal variability, and at least 30 years of data is required due mainly to the long-term persistence climatic driver (also in line to the IAHS scientific view discussed in Montanari et al., 2013) that has been reported to govern key hydrological-cycle processes for the SSL (such as precipitation and streamflow; for example, see a global-scale analysis in Dimitriadis et al., 2021, where medium and strong Hurst exponents have been found for both these processes) and cause intense hydro-climatic variabilities (for example, see the European-scale study by Blöschl et al., 2019).

Blöschl et al., Changing climate both increases and decreases European river floods, Nature 573(7772), pp. 108-111, DOI: 10.1038/s41586-019-1495-6 , 2019.

Dimitriadis et al., A Global-Scale Investigation of Stochastic Similarities in Marginal Distribution and Dependence Structure of Key Hydrological-Cycle Processes, Hydrology, 8, 59. https://doi.org/10.3390/hydrology8020059, 2021.

Montanari et al., Panta Rhei – Everything Flows, Change in Hydrology and Society – The IAHS Scientific Decade 2013-2022, Hydrological Sciences Journal, 58 (6), 1256–1275, doi:10.1080/02626667.2013.809088, 2013.

Review of „Suspended sediment concentrations in Alpine rivers: from annual regimes to sub-daily extreme events”

The authors investigate median annual suspended sediment concentration regimes for 38 gauges in the European Alps and classify extreme SSC events.

This is an interesting and timely study, and I provide some major and minor comments that should be addressed before this study can be published.

Major comments:

Abstract: Ideally, the abstract would be very easily skimmable – also and especially for an audience that is not experts in the field – to determine quickly whether or not the paper is relevant to them. At its current state, some party are rather difficult to read quickly because of the complicated wording and or long sentences. Consider replacing some words and shortening some sentences. E.g. the sentence starting in line 6: utilizing à using, maybe make two sentences out of this; there is a lot to digest here (the reader has to consider what the “annual median SSC regime” is, what hierarchical clustering is and does and what you use to run it). Also using paragraphs would be helpful for readers to find the structure better.

L 97 ff: The novelty kind of doubles with the aims of the study, and this is repeated again in the first methods paragraph (L 104ff), sometimes even with the exact same wording. I think, this can be shortened.

L 177: “Static characteristics [...] such as [...] mean daily temperature” – I would argue that temperature is not static, and I assume you would agree that there is a trend in temperatures. Thus it is important to state more exactly what you mean here (mean daily temp over which period of time? The 12 or so years you examined? Or the standard 30 years?).

L 179: I would argue that maybe the most important characteristic related to sediment availability is the presence or absence of glaciers in a catchment, but it is missing here. Maybe I don’t understand where you are going with this?

L193: there is no reference given for the actively contributing drainage area. I think it has been used/developed with respect to sediment by Li et al.? And also been used by Schmidt et al.?

L230: You tested using a different method and got similar clusters, which is great. Have you also tested for the importance of individual gauges, i.e. removing some gauges and running the clustering to see whether you still get the same results? It would be good to know how sensitive the result is to the choice of stations.  

L 294ff: I am not convinced here. If the cumulative sSSY is above average, this CAN mean that sediment stores are being depleted – OR that there has been a mass movement event and availability is greater than usual/before, which would imply greater instead of limited sed availability for coming events, right? The same goes for L 388 f.

L403: “suggesting the presence of abundant sed sources” - or rather suggesting that sediment availability is not limiting?

L495ff: I find this comparison of events to the mean soil loss rate difficult, because the latter can vary greatly between catchments – as you state yourself later. Not sure it is needed here?

L 522ff: I agree with this model assumption, and this is what Schmidt et al (2022) showed, that once areas above 2500 m become snow free glaciers also start to become snow-free and start to melt. Also compare to hydrograph separation studies such as Kormann et al. 2016, expecially figure 3 (10.3390/hydrology3010007).

L 599: This is a strong assumption. Have you tested this by applying it to a catchment that is not in your dataset? How well does it work there? If not, I think it would be good to test this.

Minor comments:

L2: detrimental impact on water use – you mean water quality?

L11: start a new paragraph as you move to events?

L13: “based on their dominant transport processes” – this raises questions rather than explaining things? I suggest to either elaborate or explain what you mean by dominant transport processes and how you get there, or remove this bit.

L 22f: “Our findings underscore the importance of [...] extreme SSC events on water quality...” – do they? Isn’t it rather that you present a new systematic way to analyze? Consider whether something along the lines of the sentence in L 87f. would be more appropriate here (improves understanding of sed dynamics not just at the local scale and enables generilazation across catchments).

L 95: what do you mean by “external”? I suggest to remove this, it kind of doubles with “between catchments” and is not necessary. This repeats later (L172), maybe in other places as well.

L 123: “reconstruct”? Maybe find a different word (reconstruct sounds like it has been there before, when really you use SSC from samples and turbidity measurements to compute continuous SSC...)

L124: this is a small thing, but technically, you use the short form NTU before the explanation in the line below.

L147: “on a finer time scale” – at higher temporal resolution?

L 263: on average 73 per catchment – can you add the min and max as well? This would help to understand the range better.

L298f: “we divided the deviation....” – this is really difficult to understand. Can you add a formula or graph to illustrate this?

L308: you mean sediment output or export not input, right? Also, Schmidt et al. have worked in these catchments as well. They also state that the glacier cover is a little lower, according to the glacier inventory of 2015. Did you calculate the glacier cover yourself?

L361: “glaciers have become snow-free” – this sounds like they have to become entirely snow-free. I think it is better so say that snow cover is minimal, because it may remain in the upper parts.

L 372f: “when we look at the average of all events per type (ignoring the outliers)...” – sorry, I don’t understand this, maybe it’s not just me and you could rephrase this?

L384f: Events partly driven by glacier melt occur once snow cover is smaller than 30%: obviously, because there is no glacier melt beforehand, which only starts once the snow cover on the glaciers is removed. Compare to Schmidt et al.

Fig. 7: some of the bars are so transparent that it is very hard to see them – at least on my device. You might want to improve this?

L 409: “three clusters [...] which are similar in terms of static attributes” – wait, the clusters are not similar right? But the stations within a clusters? This is unclear to me, consider rephrasing.

L414: The sentence starting here is very long (until L 417). Consider creating several sentences here.

L418ff: I think there are many more studies showing this (e.g. by Delaney et al., Schmidt et al., Hinderer et al., ....?). I suggest to either cite more here or say “for example” or “just to name a few” or so.

L422ff: so sediment stored in recently deglaciated moraines is then transported in subglacial channels? I think this needs to be restructured and clarified..

L 435: Schmidt et al (2023) have also shown that sediment rating curves do not work well here.

L 441: Have you considered Zhang et al (2021) as well here? (10.1029/2021WR030690)

L485: Schmidt et al 2022 use the same gauge, so it is not “in other alpine catchments”?

L512: you mean up to 280% of the AVERAGE annual sediment yield here, right?

L 525: ... Sediment concentrationS may not rise it THE sediment input is proportional to THE water input”?

L 534: I think you mean that you reset the memory manually in your calculations, correct? First I thought there was some process happening in the catchments, so I think it is important to phrase this in the active instead of passive here.

L 553: particle size, shape... and color?? (Merten et al., 2014, 10.1007/s11368-013-0813-0)

L 566: so k-means does not have the same limitations?

L 620: “shorter periods with reduced snow cover” – I think you mean shorter periods during which there is snow cover and generally reduced snow cover?

L621: increased connectivity or rather longer periods where connectivity is given or can be established?

L 624: projected and future is kind of the same.

L 647: “... the total annual sed yield of a catchment” – I am assuming this is an “average catchment”? This is debatable due to the large differences between catchments..