Analysis of Hydrologic Drought Frequency Using Multivariate Copulas in Shaying River Basin
Round 1
Reviewer 1 Report
This paper is a rebuttal of a previous one submitted to water in the 2021. Respect to the original paper the novelties of the work are properly underlined and illustrated. All my previous comments have been addressed.
Moving to the paper topic, this work represents a characterization of droughts in the Shaying river basin by using on bivariate and, importantly, trivariate copulas. In particular, trivariate copulas enhances the assessment of the return period.
I believe that this work is worth publishing in WATER.
I have just a minor request. Could the author add a figure where plotting different return period for D&S, D&P,S&P and comparing bivariate and trivariate results and return periods. This will support drought analysis and will improve the readability of the work.
Author Response
Point 1: I have just a minor request. Could the author add a figure where plotting different return period for D&S, D&P, S&P and comparing bivariate and trivariate results and return periods. This will support drought analysis and will improve the readability of the work.
Response 1: It is a great honor to receive your review comments. We have added “figure 8 Comparisons of drought frequency results between the Luohe and Zhoukou station” and analyzed. (Line443-452)
Figure 8. Comparisons of drought frequency results between the Luohe and Zhoukou station.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article is interesting for the readers of Climate (mdpi journal). However, some improvements a necessary in order to be accepted.
In the abstract please add some numerical results. This is important so as a readers have a clear view for the results of the paper regarding an abstract.
Once the specific topic is determined, the literature review needs to be performed further in-depth. Author’s needs to develop a clear logic on why the topic of this article is necessary based on the findings of the previous works that addressed the similar issue in different climatic environments. Now, I don't find such a clear logical flow in the introduction. You results may discuss further comparing with similar researches (regarding climate trends and climate change future projection on seasonal time step) recently published in Water (mdpi) and other familiar journals. Please add.
Stefanidis, S., Dafis, S., & Stathis, D. (2020). Evaluation of regional climate models (RCMs) performance in simulating seasonal precipitation over Mountainous Central Pindus (Greece). Water, 12(10), 2750.
Stefanidis, S., & Stathis, D. (2018). Spatial and temporal rainfall variability over the Mountainous Central Pindus (Greece). Climate, 6(3), 75.
Please provide a better (scale/resolution) location map for the study area
The initial datasets are coming from a network of meteorological stations. The model types of the instrumentation? Accuracy?
Trend tests are in my view the best way to investigate variability of hydrometeorological time series. Highlight the importance of drought on streamflow and the reported changes of seasonal drought (P/PET) conditions with statistical techniques in different environments (forest/lowland ect…) with some comments from other studies.
Stefanidis, S., & Alexandridis, V. (2021). Precipitation and Potential Evapotranspiration Temporal Variability and Their Relationship in Two Forest Ecosystems in Greece. Hydrology, 8(4), 160.
Serinaldi, F., Kilsby, C. G., & Lombardo, F. (2018). Untenable non-stationarity: An assessment of the fitness for purpose of trend tests in hydrology. Advances in Water Resources, 111, 132-155.
Myronidis, D., Ioannou, K., Fotakis, D., & Dörflinger, G. (2018). Streamflow and hydrological drought trend analysis and forecasting in Cyprus. Water resources management, 32(5), 1759-1776.
In the last paragraph of the intro, please state the research gap answered by this research, also state the novelty points of the proposed approach comparing with other researches.
In the discussion add some concerns for future research. For eg. If this study could be a roadmap (driver) for another analysis.
Author Response
Point 1: In the abstract please add some numerical results. This is important so as a readers have a clear view for the results of the paper regarding an abstract.
Response 1: Thanks a lot for the reviewer’s insightful suggestion. We added some numerical results in the abstract. (Line17-20)
Point 2: Once the specific topic is determined, the literature review needs to be performed further in-depth. Author’s needs to develop a clear logic on why the topic of this article is necessary based on the findings of the previous works that addressed the similar issue in different climatic environments. Now, I don't find such a clear logical flow in the introduction. You results may discuss further comparing with similar researches (regarding climate trends and climate change future projection on seasonal time step) recently published in Water (mdpi) and other familiar journals.
Response 2: Thanks a lot for the reviewer’s insightful suggestion. We have modified the introduction:
In summary, we introduced the application of SRI, copulas and trivariate copulas in hydrological drought, respectively. However, few studies combine the three in one study. In this paper, we used the SRI series and the run theory to compute drought duration (D), severity (S) and peak (P) of 1951 and 2008. In addition, we identified marginal distribution for drought duration, severity and intensity peak series, and identified the most suitable copula functions for joint frequency distribution. Moreover, we appraised the performance of four bivariate and eight trivariate Archimedean copulas, and computed the probabilistic drought properties using the best-fitted copula functions. Results of this study will further provide a framework for regarding climate trends and climate change future projection on seasonal time step in SYRB [39-40]. (Line 101-128)
Point 3: Please provide a better (scale/resolution) location map for the study area.
Response 3: Thanks a lot for the reviewer’s insightful suggestion. We added a better (scale/resolution) location map for the study area.
Figure 1. Location of Shaying River Basin.
Point 4: The initial datasets are coming from a network of meteorological stations. The model types of the instrumentation? Accuracy?
Response 4: Thanks a lot for the reviewer’s insightful suggestion. In the study, the monthly precipitation data from 1951 to 2008 were obtained from 17 hydrological stations in the basin. The equipment standards of each hydrological station are constructed in accordance with the national requirements.
Point 5: In the last paragraph of the intro, please state the research gap answered by this research, also state the novelty points of the proposed approach comparing with other researches.
Response 5: Thanks a lot for the reviewer’s insightful suggestion. We have modified the introduction in the last paragraph:
In summary, we introduced the application of SRI, copulas and trivariate copulas in hydrological drought, respectively. However, few studies combine the three in one study. In this paper, we used the SRI series and the run theory to compute drought duration (D), severity (S) and peak (P) of 1951 and 2008. In addition, we identified marginal distribution for drought duration, severity and intensity peak series, and identified the most suitable copula functions for joint frequency distribution. Moreover, we appraised the performance of four bivariate and eight trivariate Archimedean copulas, and computed the probabilistic drought properties using the best-fitted copula functions. Results of this study will further provide a framework for regarding climate trends and climate change future projection on seasonal time step in SYRB [39-40]. (Line 101-128)
Point 6: In the discussion add some concerns for future research. For eg. If this study could be a roadmap (driver) for another analysis.
Response 6: Thanks a lot for the reviewer’s insightful suggestion. We added some concerns for future research:
Since there are so many uncertainties in hydrological drought analysis including the drought events and character identification, the frequency distribution, and parameter estimation etc., proposed by some papers, many further studies on hydrological drought is still worth to be done. For example, the uncertainty of the drought threshold defined to identify the droughts based on run theory (SRI≤ -0.5 in this paper) which diminish or increase the number of droughts is still worth to be explored. The study will further provide a framework for regarding climate trends and climate change future projection on seasonal time step, and offer valuable information for the development and management of water resources in the basin. Furthermore, this study will help to better understand the droughts, to reveal droughts occurrence laws, to reduce drought disasters and to serve social practices. (Line 503-522)
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors adressed all the reviewer comments
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Analysis of Hydrologic Drought Frequency using Multivariate Copulas in Shaying River Basin
This work uses a multivariate approach to characterize from the statistical viewpoint hydrological droughts statistical in Shaying river basin with the data from 1958‒2008. Towards this aim, the standard runoff index and the run theory is applied to defined hydrological drought character variables, such as, duration, severity and intensity peak in which bivariate and trivariate copulas (function that compounds various univariate cumulative distribution functions) is used.
Authors should consult or use the water template, since the references, captions, figures placements and dimensions, equation do not follow the instructions for authors of this journal. Also, the English should be revised since through the text. Notation in tables and formulas and in the text should also be uniformed. Though the abstract is limited to 200 word it lacks a phrase with the most relevant result.
In my opinion the weakest section of this manuscript is the section of results and discussion. In my viewpoint authors make a description of the results, therefore lacks a discussion. I advise the authors to include a discussion in a separate section or with the conclusions. This section also needs to be improved, in order to clarify the results presented. Though the text is descriptive, there are some concepts that can be further developed. Therefore, in the conclusions authors can resume the main results attained with this study, having in mind the 5 main objectives earlier presented.
Figures should be improved (please consult specific comments) and all captions (figures and tables included) should be revised. Further attention should also be given to the formulas presented.
Specific comments:
Affiliation numbers do not follow mdpi instructions for authors
References in the text do not follow the mpdi instructions for authors
Abstract
Ln 12: Typo it should be 1959‒2008
Ln 12: Replace ‘And the…’ by simply ‘The …’
Introduction
Ln 57: Replace And the application… for example by Furthermore, the application…
Ln 62: brackets are not necessary in 75% and 90% if text is ‘or a percentage of 75% or 90% of it’
Ln 65: ‘…droughts, and the…’
Ln 66: Please avoid starting sentences with ‘And the…’ or ‘And therefore…’
Ln 70: viz.??
Ln 76: The same as previously advised ‘And therefore…’
Ln 92: Please consider starting this sentence with: In order to analyze drought variables… or To analyze drought variables…
Ln 99: Same as previously sentence starting with ‘And…’
Ln 112: ‘further our understanding….’?? Please re-phrase
Ln 117: please remove ‘was implemented’
Ln 120: Same as previously sentence starting with ‘And…’
Ln 132: ‘; and, (5)…’
Study area and data
Ln 150: On the other hand…
Ln 162: 2 or 4 hydrological stations?? ‒
Figure 2 lacks north arrow and scale
Captions in Figure 1 and 2 are not well formatted and should follow mdpi rules. Typo in the color of the caption in figure 2.
Methodology
Ln 171: The acronym SRI was already defined
Ln 172-173: something does not sound right in the text inside the brackets (well-known SPI??), also remove the point after precipitation. SPI if right was not yet defined.
Ln 176: the acronym CDF was previously established
Table 1: Caption does not match the contents of the table, SPI or SRI??
Ln 194: typo in ‘… ,. So …’
Ln 197: In Figure 3, D …
Ln 203: Once more ‘And…’
Ln 205: The -1, -0.5 should be with the ‘minus’ signal ‒1, ‒
Ln 208: (e.g. Figure 3 a and f)
Ln 209, 212, 203: Figure number missing inside brackets
Ln 229: remove spaces between F1 and (x2) the same for the other two functions
Ln 231: the same as for 229. Point missing in the end of the formula.
Ln 237: remove space before point
Formula 2 remove italic format
Ln 242: typo where and not Where
Ln 246: are used
Formula 3 remove italic format
Ln 253: typo where and not Where
Ln 270: Tand, and should be subscript as in formula (4)
Ln 271: Tor, and should be subscript as in formula (5). Space missing before brackets (OR…
Ln 272: space missing before u ; same as for Ln 270 and 271
Formulas (4) and (5): n is not defined
Ln 277: same as for Ln 270 and 271
Formulas (6) and (7): W is not defined
Results and discussion
Ln 288: Again…’And…’
Ln 292: units missing for P
Table 2. times or number of events?? Please clarify
Ln 298: Again…’And…’
Ln 304: Once more ‘And…’
Ln 315: Once more ‘And…’
Ln 319-320: The statistical values
Tables 3 and 4: captions are not equal please consult instructions for authors or use the template given by the journal
Ln 333: were higher than 0.5
Ln 334: Again…’And…’
Ln 335: Due to the dependency, (revise space between the words in this sentence)
Figure 4: reformulate this figure, captions inside the figure are overlapped with the axis numbers
Ln 356-358: This sentence ends in suspense; the idea is not complete. Please re-phrase-
Figure 5: this figure is not complete. In its caption please replace & by – as presented in the text
Ln 364-365: please re-phrase
Ln 367: typo when and not When
Ln 368: probability increases from 0.1 …
Ln 369: probability rises from 0.1
Ln 370: probability is up
Ln 387: space missing between ° and diagonal
Ln 392: taken the result
This sentence also ends in suspense; please remove the and in Ln 392, and replace were by are
Ln 396: typo when and not When; probability increases from 0 to
Why are these sentences written in the past??
Figure 6 and 7: Again, captions…
Ln 409: typo 50a
Ln 410: Tand and Tor, as previously recommended (please revise throughout the text)
Table 7: remove . from Hydrometric; Ta and To were not proper defined. Authors refer to Table 7, but present results regarding Tand and Tor in the text. For me this should be clarified.
Ln 427: space missing before 51%
Ln 438: As for Tand and Tor, the a and o in Ta and To, should be subscripts as shown in Table 7. Please revise
Ln 440: Conversely, Ta
Ln 492: space missing after brackets
Ln 500: best knowledge, the (remove extra space)
Ln 507: Since there are
Ln 511: uncertainty of drought
Ln 512: which diminish or increases the number of droughts is still worth to be explored.
Ln 513: And…
Ln 517: under global climate change conditions, as well as human activities impacts…
Ln 518-519: Further study, further work? Please revise
References are order by appearance and not by alphabetical order. Again, consult the author’s instructions, since they also all need to be properly formatted.
Reviewer 2 Report
This paper applies bivariate and trivariate copulas in order to study droughts in the Shaying River Basin. Appreciably, the authors use both symmetric and asymmetric Archimedean copulas. Despite a big efforts has been clearly made, I have no clear what are the novelties in this work. Probably this is mainly due to the fact that the introduction is not properly written. This paper indeed is mainly focused on droughts analysis in the Shaying River Basin but we do not know if previous work has been made about droughts in the same region. On the other hand, the introduction seems to be more focused on the “history of copulas” but no novelty has been introduced in this work related to that.
Consequently, I would suggest writing a proper introduction (and consequently conclusion and abstract) where the authors should clarify: what we know about this topic (droughts) in the selected region of interest; how this study will advance our knowledge about droughts in the selected region.
Some other minor comments:
Abstract: The sentence “Droughts, considered as one of the most dangerous and costly water cycle expressions, occurred always over a certain region, lasting several weeks or months, and involving multiple variables” sounds from a grammatical point of view incorrect. Please check it, particularly, comas and verb tense structures.
Line 37: The sentence “Hydrologic drought caused by streamflow deficits is one important type of drought event” seems a tautology. Could the authors reframe it?
Line 42: Could the author better specify “traditional approaches ”. They seem more “old”. It's quite common nowadays the adoption of multivariate approaches for assessing droughts.
Lines 142-157. Could the authors provide more references for the “Shaying River Basin” study area. There are too many statements not supported by a proper literature review.
Figure 3: Could the authors expand the caption of Figure 3. Many details, in my opinion, are missing.
Line 241. I think that the letter should be capital
