This study presents a compilation of hydraulic head measurements from polder regions across the Netherlands and conducts a data-driven time series analysis of current and future trends in head. The authors find that a non-linear threshold model best reproduces the observed data, and observation data may be clustered into 4 groups based on coincident observations of peak head in space and time. Under four different climate scenarios, changes to the return interval of extreme head values may be negative or positive because future outcomes depend on the change in future hydroclimatic variables. This study is likely to be of interest to the scientific community, particularly to those involved in hazard assessments of low-lying canal dikes. I look forward to seeing it in print.
The manuscript would benefit from a round of minor revisions. Suggested edits to improve the manuscript primarily relate to manuscript organization. There are multiple places where content in the Introduction, Methods, and Results would fit better in a different section. In addition, the results of the climate change analysis are interesting and will be of interest to the community, but they merit further attention in the Discussion section. Lastly, there are some grammatical errors to resolve. Specific recommendations on each of these themes (as well as a few minor ones) are presented by line number below.
Line 12-13: I recommend rephrasing this sentence to: “These models were used to simulate 30-year time series of head under current and plausible future climate scenarios.”
Line 56: remove comma after “heavy rainfall event”
Lines 84-98, and Figure 2: This paragraph and Figure 2 are useful to understanding the methodological framework of the study, but they feel out of place in their current location at the end of the Introduction section. This paragraph and figure summarize the Methods used in the study; for this reason, I suggest moving both the paragraph and Figure 2 to the very start of the 3. Method(s) section, before section 3.1. This will fit more naturally within the structure of the manuscript and will give readers a helpful summarization of methodology right before diving into all of the details. Note that this change will also require renumbering Figures 3 & 4 and their respective references in the text. The final sentences of the previous paragraph (i.e., lines 78-82, starting with “This study aims to…”) seem like a more natural end to the Introduction section, as they provide a general roadmap of the study. The authors may also choose to expand on the roadmap with an additional statement or two on the novelty of their approach and the research gap that they address.
Line 85: the acronym “IRF” is defined in three separate places in the text (here, line 193, and the caption of Table 1), but “IRF” is only used as a column header in Table 1. I would recommend removing this acronym from the text since it is not used, or alternatively, replacing the following instances of “impulse response function” in the text with “IRF”.
Line 89: remove comma after “resulting in a set of models”
Line 110: fix spelling of “focusses”
Figure 4: I find this figure to be very helpful. One recommended change: it is not clear on first glance what is meant by the terms “90th percentile profile” and “10th percentile profile" – my first interpretation was that they referred to the phreatic surface profiles. These terms are eventually defined as points drawn from elevation profiles on line 309. Please make this clearer in either the figure itself or in the figure caption.
Line 197: the index of summation under the summation symbol is a capital “M”, the same as the upper bound of the summation. Should this be a lower-case “m”?
Line 205: I understand that the authors use more than one type of response function (e.g. exponential, gamma) that are not defined in the manuscript. This seems fine, but can the authors provide a citation here to point interested readers to a resource with fuller descriptions of the response functions?
Line 215: this water budget does not include surface runoff (follow-up: as described in the Discussion section 5.1); is surface runoff unimportant/less relevant to polder canal hydrology? This merits a brief mention here, too.
Table 1: please replace all instances of “lineair” with “linear”
Lines 246-249 and Figure 5: These results belong in the Results section.
Line 296-298: though not entirely clear, this sentence seems to imply that only the exponential distribution was used throughout the study. If this was the case, then for clarity, I would recommend removing the discussion and definition of the general form of the generalized Pareto distribution and instead define just the exponential distribution. If not, then please clarify where/how the Type I, II, and III distributions were utilized in the text.
Line 310: as with “IRF”, the target levels acronym “TL” is not used in the text (other than in Figure 4) and should be removed. Its definition in the caption of Figure 4 should remain.
Line 317: “clusters of dikes” is mentioned here, but no methodological details are provided. They are instead described later in the Results section 4.2.1 (lines 394-411). Most of the paragraph on lines 394-411 belongs in the Methods, not the Results.
Section 4. Results: there are several places where interpretation of results (and attribution of causes behind the results) are included in the Results section but likely belong in the Discussion section. Moving them would help focus the reader’s attention on the results of this study while helping to bolster the discussion of study results within a wider scientific context, which is largely missing from the Discussion section. In general, I encourage the authors to more fully differentiate presentation of results in the Results section from interpretation of results and their connection to past work in the Discussion. The lines below are suggested places to consider moving content from the Results to the Discussion:
• Lines 379-386: beginning with “The difference in response time can be…”
• Lines 473-479: all sentences on these lines
• Parts of lines 498-503 that infer explanations for the results
Line 330: recommend using “Therefore,” in place of “So,”
Figure 6 and lines 350-351: what is “A” in the block response plot? It seems to be the peak response value. Additionally, lines 350-351 state “The peak of the block response represents the maximum increase in head level that would occur,” implying that the block response has dimensions of length (e.g., units of meters), but the y-axis label in the block response plot is “Response [-]”, implying it is dimensionless. Can the authors please clarify?
Line 425-426: This first sentence is unnecessary; it can be removed without loss of detail.
Lines 464-466: The definition of decimate height and how it is used would be more appropriate in the Methods section, probably section 3.2.
Line 485: little information is provided in the manuscript on the climate change analysis portion of the study. Greater description of the datasets presented in section 2.2.2 would be helpful to the reader, i.e., fuller descriptions of SSP5-8.5, SSP1-2.6, and the wet- and dry-trending scenarios that were introduced on line 176. Sentences from this section that describe methods should be moved to an appropriate section in the Methods (e.g., lines 485-488, the definition of the probability factor on line 494-495). The authors might consider a new section at the end of the Methods to bring the descriptions of climate change data and methods together in one place.
Line 502: the authors state that the “precipitation increases” in the climate scenarios with drying trends; this seems like a contradiction, although it may not be. Perhaps additional details on the methods behind the climate-change analysis (as suggested above) would alleviate this confusion.
Lines 503-504: The authors state “For climate scenarios in 2100 with a wetting trend, the frequency of occurrence of extreme load levels is increasing,” but the right plot in Figure 11 seems to indicate that the low-emission, wet regional response scenario (Lw) results in little-to-no change in probability factor. Please clarify.
Line 516: change “Frist” to “First”
Lines 629-631: One important aspect of the Conclusions and the Abstract is that extreme peak heads “…are expected to occur between 3 times less and 8 times more frequently by 2100, depending on the climate scenario and the type of canal dike,” but this statement is not expounded upon in the Discussion. In addition to the above-mentioned modifications of the Results/Discussion sections, I would recommend a few sentences in the Discussion that explicitly tease this conclusion apart. For instance, under which specific scenarios (and timeframes) do the extreme peak heads tend to become less frequent, and under which do they become more frequent? The right plot in Figure 11 also shows some interesting results that are not discussed: the high emission + drying scenario (Hd) shows large declines or no change to the probability factor in 2050 but generally shows increases in 2100. Likewise, the high emission + wetting scenario (Hw) shows a slight increase in 2050 but a much larger increase across the board in 2100. Can the authors infer any causes behind these temporal trends? Finally, a discussion of precipitation seasonality is mentioned in the Abstract, Introduction, Conclusions, and the Appendix, but is almost entirely absent from the Discussion. Trends in seasonality and the importance of the type of canal dike when considering future climate conditions should be explicitly commented upon in the Discussion. |
