Unraveling Regional Patterns of Sea Level Acceleration over the China Seas

Round 1

Reviewer 1 Report

In this study the authors analyze sea level accelerations along the China coast and also in the China marginal seas using multi-source dataset. The steric and mass contributions are explored. The role of climate variability in modulating the accelerations is discussed. Overall, this is a useful study and the results are straightforward. Below I have some comments for the authors. A bit Language polishing is also necessary.

L15-16 Sorry – can’t understand this sentence

L18 why do you say altimetry “underestimate/overestimate” sea level acceleration? It seems you trust tide gauge more? Why?

L22 what does “strengthening pattern of sea level acceleration” mean?

L24 “none steric component” – can you just say “mass component instead”

L55 where is NPQB? Near which city?

L81 what does IAP mean

L120 also reference 27 using similar way to calculate acceleration

L123 more details about filtering

L126 “accelerations” here and other places

Figure 1a longitude/latitude ranges could be smaller

Figure 1b using equation 1?

L144 can’t understand how the results suggest “20-30 yr oscillation”?

Figure 2 this figure seems NOT necessary at all

Figure 3 from the caption I can’t understand how this figure was derived; Year in X-axis means middle year of the time window?

L194 explain TG, ST, AL here

A bit Language polishing is necessary.

Author Response

We are grateful for the critical comments and suggestions from the reviewer. We have responded to all comments below, our response is in italics, quotes and modifications from the manuscript are highlighted with yellow. Please see the attachment for all details.

Author Response File: Author Response.docx

Reviewer 2 Report

This study analyzes sea level acceleration in China's seas and coastal areas and the drivers of short-term and long-term acceleration patterns. The authors used both tidal gauge records and satellite altimetry data. Using variable analysis window lengths, they identify short-term and long-term patterns and compare the satellite altimetry data with gauge records. Furthermore, they consider the effect of ENSO and PDO variability to assess its impact on sea level acceleration and provide information on how components and drivers of acceleration may vary in seas and coastal areas. Overall, the study provides insights into sea level acceleration from steric and non-steric components in China's seas and coastal areas and identifies the potential and limitations of such analysis with the available data.

1) I suggest the authors include more background information on different components contributing to sea level acceleration and the effect of ENSO and PDO.

2) Line 14-16: I suggest the authors rewrite and make this sentence clearer:

“Since 1950s a wide range of acceleration in tide gauge records reveals that coastal sea level is dominated by low frequency variability up to 30 years.:

3) Line 46-47: The sentence is not clear.

“and it remains a lack of understanding of physical mechanisms underlying processes of sea level acceleration along the coast of China.”

4) Line 70: There is a formatting issue for URL of the data source it goes to the next line in the middle of the line.

5) Line 75: The authors state that NCEP data is used to inverted barometer correction of gauge records. Why not mention this in the previous section when the gauge record data are explained. Also, how the satellite altimetry data was corrected?

6) Line 107-108: The authors state they have removed annual and semi-annual cycles but there is no mention of how they did this.

7) Line 117: The authors state that they assume residuals are pure noise. Is there any justification for this?

8) Line 179-180: The reference to the Figures is unclear. Did the authors mean: “open ocean (Figure. 4a) is statistically significant and in agreement with steric sea level acceleration (Figure4 b)?

9) Line 183-188: The authors first state that after removing ENSO and PDO variability the sea acceleration becomes stronger, then at the end they state that this reveals steric changes through ENSO and PDO variation are mainly driving the sea level acceleration. I would ask the authors to clarify this since they seem to be contradictory. Authors should clarify this parts.

10) The is a typo in line 292: “deceases”

11) The reference section is very dense and may be difficult for readers to navigate. I suggest the authors modify this to make it more readable.

12) The quality of most images should be improved.

The English is generally fine. Some sentences should be improved for clarity. Please refer to the comments. 

Author Response

We are grateful for the critical comments and suggestions from the reviewer. We have responded to all comments below, our response is in italics, quotes and modifications from the manuscript are highlighted with yellow. Please see the attachment for all details.

Author Response File: Author Response.docx

Reviewer 3 Report

Line 11: Instead of '...sea level are...' consider '...sea level is...'.

Line 11: Instead of '...the processes remains...' consider '...the processes remain...'.

Lines 40-41: I find it hard to believe that future development and adaptation plans are requiring robust scientific evidence. Can you provide examples? My understanding is that we reached a consensus as you stated in line 34, and that the evidences we have so far are strong enough to support the necessary actions towards adaptation/mitigation. So please ellaborate on this.

Lines 45-47: Authors need to add a short review on: (i) Role of specific contributors od SLR to the patterns observed in China (ii) Physical drivers of SL Acc. worldwide and how/why these should be different in the China Seas and Coasts.

Line 51: Is there any particular reason for chosing ENSO and PDO over all the remaining physical mechanisms?

Line 60: The sea level acceleration should be described in detail under the heading "2.2 Sat altimetry" for the sake of tidiness. So is the mention of correction of Inverted barometer effects that are scattered over Sections 2.1 and 2.2

Table 1: Instead of "years" use "record length in years". Also add a not ethe table legend because the record lengthand this table are referred to in Results section. 

Lines 81-86: What is meant by 'IAP'?

Line 87: I would like to see a sentence or two that elucidating calculations in GRACE area completely different, and use different dataset from that of the Satellite altimetry. Otherwise, there would be no point in comparing in the two.

Line 107: There is not novelty in the approach adopted, as it has been used bofore, for instance in https://doi.org/10.1016/j.asr.2020.01.016, however, the authors make no effort to critiically appraise or simply mention these earlier endeavours. What is the rationale for the comment on lines 113-114 (Vertical land motion such as Glacial Isostatic Adjustment does not 113 affect the sea level acceleration.)? It should also be noted that when using Eq.1 it is assumed that SL acceleration is constant over the period under consideration, which may not be entirely true. What are the implications of this and other assumptions amde with this approach?

Lines 118-124: By including MEI and PDO in the list of predictors one assumes that each one of them are linearly related to the outcome 'h'. The relation between predictors, or the "the contribution of ENSO and PDO variability to acceleration (2*a2)" would have to be determined by other means. Authors need to clarify in the "Methods" how such contribution is actually calculated and examined. 

Line 117 and 121: Eqn 2 states that the residuals of Eq1 are not exactly 'pure noise' and that it carries a contribution of ENSO+PDO to the Sea Level.

Lines 112 and 122: Since annual and semiannual cycles have beem removed fro Sea Level records, it sounds incorrect to call 'h' sea level time series.   

Lines 115-116: Authors shuld briefly explain what polyfit and polyparci are (the main ideias behind these) for those readers that are not familiar with 'MATLAB'.

Line 123: What consisted the filter of Zhang and Church? Is it a high/low pass or a windowed filter? Please give a brief description (1 sentence only if possible).

Lines 134/135: The locations Lusi and Shek Pik are not easily visible in the map of Fig-1. This needs to be corrected. Also, I fund it impossible to read the values -0.05±0.04 and 0.41±0.32 in the figure. Same goes for the dependance of acceleration on the length of time series

Lines 141-142: I do not understand how come there are many acceleration values in Fig-1a when Equations 1 and 2 allow only a single value to be determined. What are the different colours in Fig 1b or 2a?

Line 156: "Study area" was not formaly presented. So, I am not sure what is meant by it in this line. Is it the entire China seas, is it the location of all 21 Tide gauge stations illustrated in Fig-1a?   

Figure 3: I am not sure the interpretation of Fig3 is correct because I can't figure out how it was produced. If it is a wavelet then the interpretation should read different. The window length in months should indicate periods (or frequencies?) in which a particular sign is strong/weak, normal/reversed, etc. The t-axis should indicate how long the sign remanined in a particular state. But again, please clarify how come there is a timeseries for acceleration if equation 1 or 2 were used?  Also, judging by the units of acceleration, my first guess is that there would be one value per year if the polyfit function were applied for each 12 consecutive datapoints. 

Figures 1b and 2a show the same information with a minor difference. They should be presented in the same figure to allow for better comparisons.  

Table 2: The value -0.00±0.00 is meaningless and should be revised.

Line 183-188: Long sentence, consider revising.

Line 190: I had stopped checking language, however where it reads "...remove ENSO..." must be corrected to "...remove ENSO effect...". Also, since MEI was used instead of ENSO, then all the docuemnt should be consistent about it and maintain only MEI. 

Line 198: Again, it wrong to write PDO (mm/yr2) as these units pertain to acceleration.

Line 204: Only six coloured circles are visible when 21 were expected. Please explain in the text.

Figures 5 - 10: Authorus need to properly introduce these figures and guide the readers through them, pointing the mains aspects one should pay attention to. Same goes the many tables in between these figures.

Line 245: When comparing the two acceleration estimates I expected to read what similarities/differences were found by the authors, but no those were not mentioned. Please revise.

Line 252: The consistency here is iinferred from mere visual inspection of maps that contain both posetive and negative patches of accelartions (both showing increasing trends). The authors should find quantitative means to evaluate the consistency, and therefore present a more robust evidence that mass redistribution is the main driver of (coastal) acceleration. I am not convinced this understanding is limited to the coastal zone.

Lines 245-255: The patterns described in these lines are not ubiquitous and deviations from the dominant pattern need to be addressed.  

Line 268: Something was mentioned about vertical land motions not being considered in the determination of regression coefficients, including acceleration. So, it is not clear how growndwater extraction (i.e., vertical land motion) is now used to explain discrepancies. 

Line 313: The statement in this line is still a mere suggestion and should remain as such until conclusive testing has been made.

Line 369: Not exactly true,....onl the sources of the data were given in the paper, and that is sufficient. The wording should reflect that.

The authors need to conduct massive language editing, probably through paid services if no native english speaker is available to proofread. I had problems erading and understanding entire paragraphs.

Author Response

We are grateful for the critical comments and suggestions from the reviewer. We have responded to all comments below, our response is in italics, quotes and modifications from the manuscript are highlighted with yellow. Please see the attachment for all details.

Author Response File: Author Response.docx