the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jan 2025
Morphological response to climate-induced flood event variability in a sub-arctic river
Abstract. This study examined the effects of climate-induced flood event variability and peak sequencing on the morphological response of a sub-arctic river. We classified 32 years of discharge hydrographs of a sub-arctic river in terms of their flood event shape variability and peak sequencing, and linked them to seasonal and annual climate conditions. We utilised morphodynamic modelling to examine the effects of the flood characteristics on the morphological response of the river. The findings highlight the critical role that discharge hydrograph shape and sequencing plays in shaping river morphology and sediment transport dynamics. The increasing frequency of double-peaking floods, associated with higher geomorphic activity and sediment loads due to rising temperature and precipitation amount, points to alterations in the morphological response of the river channel. This suggests a gradual change in long-term morphological adjustment and potentially a gradual shift in sediment transport regime in the future. These shifts could have long-term implications for river stability, sediment connectivity, and ecosystem dynamics. Even in regions where hydroclimatic changes are not yet fully visible, the flood event characteristics can be evolving and re-shaping the morphodynamics of the river channel. The study underscores the importance of catchment-scale assessments and future research into the combined effects of flood sequencing, sediment transport, and changing hydroclimatic conditions.
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Status: open (until 27 Mar 2025)
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RC1: 'Comment on egusphere-2024-3802', Anonymous Referee #1, 09 Feb 2025
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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
Citation: https://doi.org/10.5194/egusphere-2024-3802-RC1
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