I appreciate the opportunity to review this insightful manuscript, which examines the impact of climate-induced flood variability on the morphological changes of a sub-arctic river. The study addresses a critical issue in river geomorphology, offering valuable insights into how climate change affects sediment transport and river morphology in cold regions. The 32-year dataset and morpho dynamic modeling are significant strengths, providing both observational and computational perspectives on climate-induced changes in river systems.

From my point of view, the manuscript offers valuable and very timely contributions to the field. However, there are areas that could benefit from further refinement. Incorporating recent studies on warming-driven erosion and sediment transport, particularly in permafrost areas, would broaden the context. Additionally, the manuscript would be strengthened by more empirical evidence, such as observable morphological shifts, to support claims regarding sediment transport dynamics during multi-peaking floods. A clearer explanation of the methodology and its limitations would improve the transparency of the analysis. Finally, a deeper discussion on the role of permafrost thaw and riverbank erosion would enhance the manuscript's relevance to current hydrological and geomorphological research.

Overall, I would recommend a moderate revision.

Major Comments:

 Lines 40-47:

The introduction and discussion provide a solid overview of the impact of climate change on river morphology. However, I believe it would enhance the manuscript to compare with recent studies addressing warming-driven erosion and sediment transport in wider cold regions in a more detailed way. This could place the study in a broader context, providing a more comprehensive framework and thus potentially broadening its appeal to a wider audience. Many sub-arctic rivers drain through frozen landscapes. I also wonder whether the catchment is a catchment with permafrost and seasonally frozen ground and this aspect should be better introduced in the introduction. Please check the permafrost map (https://www.sciencedirect.com/science/article/pii/S0012825218305907) and add such information in the study area Figure 1. Also, some new progress for permafrost river dynamics under climate change are: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL112752; https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL111536;

Lines 440-450:

In the " 5.2. Flood event types and morphological response" section, I believe it could benefit from an explicit reference to permafrost dynamics. The thawing of permafrost significantly impacts riverbank stability, which in turn can alter sediment availability and transport processes. This factor is absent from the manuscript. Additionally, the discussion of future morphological changes mainly emphasizes increased sediment loads due to hydroclimatic shifts, but it would be important to also consider potential changes in riverbank erosion and meander migration rates, which are highly relevant in the context of permafrost thaw and sediment transport dynamics.

Lines 452-462:

The study suggests that the increasing frequency of multi-peaking floods could lead to long-term shifts in sediment transport regimes, potentially destabilizing the channel. While this is a valuable observation, the evidence provided seems to be inferred rather than directly demonstrated. It would greatly strengthen the argument to present evidence of observable morphological shifts in the study reach over the 32-year period. For instance, a comparison of historical channel adjustments (e.g., planform changes, bank erosion rates from in-situ or remote sensing observations) would provide empirical support for the claim of long-term changes in river morphology due to the increasing frequency of multi-peaking floods.

Minor Comments:

 Lines 167-171:

In the "3.2. Hydrograph classification" section, the study classifies flood hydrographs into four distinct categories, but I feel that the rationale for selecting the 75th percentile (p75) as the threshold for flood discharge could be further explained. Why was this specific quantile chosen? It would be valuable to explore whether other quantiles (e.g., the median or the 90th percentile) might result in different classifications and what implications such variations could have on the analysis. Providing a clearer justification for the chosen threshold would enhance the transparency of the methodology.

 Lines 178-184:

While the study classifies flood events based on peak sequencing, it does not address whether these sequences are driven by intrinsic hydrological processes (e.g., soil moisture memory, antecedent conditions) or external climatic factors. A more detailed discussion of the underlying drivers of peak sequencing would add depth to the analysis and potentially strengthen the study's conclusions by clarifying the factors that influence flood event sequences.

Lines 327-335:

The analysis suggests that sediment transport rates during the second peak of multi-peaking events are lower than during the first peak, which is consistent with previous findings on sediment depletion. Nevertheless, it would be valuable to consider whether there is any evidence of hysteresis reversal due to finer sediment contributions. If possible, separating the suspended sediment and bedload data in the analysis could provide a more comprehensive understanding of the sediment transport dynamics during multi-peaking events.

Figures 1-9:

Some of the figures would benefit from clearer labeling, particularly in the distribution of climate data and the identification of flood event types. Additionally, ensuring that the legends and axis labels are consistent across the figures would enhance clarity and facilitate easier comparison of the results.

Dongfeng Li

This is a nicely written paper merging field data and morphodynamic modeling to understand how (a) how climatic changes modify flood characteristics and [by consequence] (b) how changing flood characteristics impact the morphological response to floods of a sub-artic river. The stated aims of the study are to:

i) Analyse and classify the variation in flood event hydrographs over the past 32 years in a sub-arctic river

ii) Link the flood events to seasonal and annual climate conditions, and 

iii) Evaluate the channels morphological response distinctive to each flood event type utilising morphodynamic modelling and sediment hysteresis analysis

These aims are obviously very important given the rapid environmental changes occurring in sub-arctic environments, and I think the authors have nicely achieved their stated aims in the paper. However, there are several aspects of the paper which I think are slightly lacking. For this reason I suggest that the work would be excellent for publication in ESurf after some minor/moderate revisions centered around the following two concerns:

Main comments:

First, the presentation of the morphodynamic modelling results is a little bit "black and white", in that the authors do just four simulations with a set of parameters taken from their group's earlier papers, then they discuss the outcomes of these simulations in a definitive <> type of way, when in fact, the input parameters of these simulations are uncertain and the outputs will definitely depend on them. At the same time, the morphodynamic modelling must lack processes contained in the real world (sediment transport fluctuations?, realistic width changes?, vertical sorting? 3D flow effects? frozen vs thawed banks? within-channel ice?), although the potential lack of any such processes is not acknowledged in the methods or discussion. The reader may naturally be curious as to how robust the authors' modeling conclusions are on erosion and deposition patterns (Figure 9), net sediment budget across hydrographs (Paragraph at 359), stream power trends, and hysteresis patterns for the different hydrograph types they define (Figure 8), and other things. Clarifying the sensitivity of the simulation results on the inputs and model assumptions might be possible with an additional paragraph in the results. The limitations of the modeling approaches might be  described in additional text in the methods or discussion.

The second comment concerns section 4.1 in the results. As the reader arrives at this section, you have previously defined the four different flood-event types: high one-peak floods, low one-peak floods, two separate peaks, and wavy peaked floods. The sorting of your observed hydrographs into these four categories is nicely laid out in Figure 3, where the "typical" hydrographs of each type are shown as red lines. However, the climatic data show only rather weak differences across categories in almost all cases. The box-plots in Figure 6 show that climatic variables are similar (overlapping) across event types. This overlapping makes it tough to believe the claims in 260-272 at face value. With more or less data, we could easily imagine making other conclusions. Can the authors do something more quantitative to strengthen their claims despite the necessarily limited sample size? For example, "High annual and low springtime precipitation were linked with high peak floods". "Wavy flood events (D) experienced the warmest temperatures, high amount of snow, 270 and high levels of both, annual and spring precipitation (Fig. 6)" What do you have for the reader who sees four overlapping box plots which show no significant distinction? In my view this is a pivotal issue since one of your key points is that "each flood event type could be linked to slightly different climate conditions", while it's not immediately obvious that this is the case looking at Figure 6. I would suggest some additional statistical analyses could be added (maybe ANOVA to find significant differences with a given confidence?) to strengthen the claims near lines 260-272.

Secondary comments:

• 47 run-on sentence
• 54 run on sentence
• 60 awkward sentence
• 65 Suggest an edit of this sentence, such as "... through analysis of sediment transport hysteresis patterns, which reflect..." as it's currently a bit awkward seeming
• 71 run on sentence
• 74 You alternate between using oxford commas and not using them. You might aim for consistency in this.
• 89 It may be useful to share the bankful width of the river to give more sense of scale.
• 93 run on sentence
• 96 and both the Atlantic ocean and ...
• 100 you never use the abbreviation "a.s.m.l." again, so I guess there is no need to define it.
• Figure 1 - it is not immediately clear to me what "1, 2, 3" marked on the map mean, although it comes together when I stare at the figure a bit. You might add explanation of these numbers in the figure caption
• 123 I am wondering at this point exactly how often the sediment transport samples were collected
• 128 This should be a colon, not a semicolon: "... based on a combination of field ata were generated: ..."
• 133 intervals
• Fig 2A - "WL m" I infer to be "water level" but this is not defined - the figure caption calls it "x". Suggest to say "Regression curve between discharge measurements (Q) and LeveLogger water level (WL) in ...". Also I noticed at 381 you refer to "x" and "y", which I guess is clear enough as "horizontal axis" and "vertical axis", but it may be better to just say the name of the variable you're speaking about.
• Fig 2B - the regression made between Pulmanki and Tana looks overfitted, since it decreases at large discharges. Why would the discharge in Pulmanki decrease when Q increases beyond 2200cms in Tana?
• Table 1 - several quantities here are not defined in the paper. What are MAE or SDE? What is "n" - Manning? The notation of R-squared is typically written `R^2`, with a superscript. Is r a Pearson correlation coefficient or is it \sqrt{R^2}. A definition is needed for these variables. Maybe you can add it to the Table description.
• 168 - Figure 6 shows also April floods lumped in with may and june. Should you say April, May, and June here?
• 172 - it is natural to wonder how your analyses would vary with changes to your definition of 40cms for a high flow or to your savgol filter parameters. This is a similar-in-spirit comment to the major comment #1 above. In addition, your analyses would not be completely reproducible without details of how you set the peak-finding parameters (prominence, width, etc) in scipy.signal.find_peaks. I think a few sentences about sensitivity and further explaining your peak finding strategy would improve the reader's confidence in your results and enhance reproducibility.
• 181 I have seen up to now many examples in the paper where compound adjectives are not hyphenated, e.g. "precipitation-driven discharge peaks", "high-lattitude rivers", "flood-event shapes", "one-peak flood", on and on. I would suggest to search the paper for compound adjectives and add hyphens everywhere applicable, as this makes the reading smoother and reduces any chance of misunderstanding.
• 195 were selected
• 198 precipitation event magnitudes? Or occurrence of precipitation events?
• 206 to identify
• 207 recurrence or occurrence?
• 209 MK is defined here but not M-K strictly speaking
• 209 error in citation formatting
• 211 removed or compensated for, not neglected I think
• 220 here I am still wondering about the frequency of sediment sampling and how this compares to your detailed dataset on hydrological variables
• 220 intervals
• 221 the gradistat program, the method of moments, a logarithmic distribution (missing articles "a" and "the", I also have seen other places in the paper with this small error)
• 236 model's geometry (apostrophe in wrong place)
• 237 run-on sentence
• Table 2 - suggest to format m3 as a superscript m^3
• 254 Section, not chapter
• 255 from the field
• 260 it's confusing how you speak of "flood events A-D" in this particular section. You use singular tenses, as in "The wavy event D had an average duration of 9 days" which suggests you're using the typical events, i.e. the Red curves from Figure 3, but rather you are using all events of a particular type A-D in this particular subsection. I suggest to speak of "flood events of type A" and so on, in a plural tense. It should be clear you're discussing the statistical outcomes of many floods. Another example - you say "it had more variability than type B", but you really mean "the flood events of type A had more variability than those of type B" and so on.
• 267 what type of preciptation amounts?
• 268 it -> flood events with two separate peaks
• 277 "In general, there were more variation in spring variables than annual variables, which implicates that the hydroclimatic conditions preceding the spring flood impact the flood event type more than the prevailing spring conditions." - Are you sure? Could the larger variation in spring variables not be simply that the spring sample size is smaller? (implicates -> implies)
• 334 and in Figure 8. The linkage between hysteresis type and hydrograph shape seems to me to be a very nice result that is worth emphasising. Currently this is not mentioned in the abstract or key points, although "hysteresis" is in the keywords.
• 426 you refer in the paper to "sediment hysteresis" but it's not hysteresis of the sediment, it's hysteresis of the sediment transport. I suggest to modify everywhere to "sediment transport hysteresis"
• Figure 9 shows beautiful patterns of erosion and deposition in your morphodynamics simulations of the study reach. I guess it would be possible to make videos of the channel evolution across the four hydrograph types rather easily. This would make a nice addition to the paper as supplementary info which would increase its visual appeal and show how the erosion/deposition and sediment export differences between the four event types you've defined actually arise. I would suggest if it's easy enough, you might make these videos and integrate them into the text with a few sentences of discussion. This would strengthen the paper