Evolution Characteristics of Meteorological Drought under Future Climate Change in the Middle Reaches of the Yellow River Basin Based on the Copula Function
Round 1
Reviewer 1 Report
Dear Authors,
I suggest to have the manuscript checked by a native English speaker. Many sentences are difficult to comprehend.
The novelty of the study is not sufficiently explained.
The conclusions not give an adequate summary of what has been intended, the novelty and the outcomes of the study.
I recommend to improve these aspects.
Kind regards
Needs to be improved. There are several vague sentences.
Author Response
Reviewer #1
- I suggest to have the manuscript checked by a native English speaker. Manysentences are difficult to comprehend.
A: We have asked MDPI to polish the English of the manuscript.
- The novelty of the study is not sufficiently explained.
A: The academic contribution of this paper had been added in our introduction as follow: In the current study, a Copula function based drought identification method for future multi-discharge scenarios was established. Based on the run theory, drought events were identified and drought duration, drought intensity and drought intensity were extracted. The optimal distribution function was selected as the marginal distribution of drought characteristic variables. Based on the optimized Copula function, the joint return period and co-occurrence return period of drought duration and intensity, duration and intensity, and intensity and intensity in the middle Yellow River were deduced. The identification of future drought in the Yellow River Basin under SSP245 and SSP585 discharge scenarios was realized.
- The conclusions not give an adequate summary of what has been intended, the novelty and the outcomes of the study.
A：we had revised the conclusions as follow:
This study is based on run theory and combines copula functions to establish a method for identifying future multi-emission drought scenarios in a watershed. Drought events in the watershed were identified, and the drought duration, drought severity, and drought intensity under current and future climate scenarios were extracted. The current drought trend in the middle reaches of the Yellow River is worsening, and the drought severity shows a decreasing trend under four future climate scenarios. Based on the copula function, drought events with short duration, low drought severity and weak drought intensity are more likely to occur in different zones of the Yellow River Basin under historical and SSP245/SSP585 emission scenarios. The order of occurrence is generally Ta(D&I) > Ta(S&I) > Ta(D&S), and the joint return period follows the order To(D&I) < To(S&I) < To(D&S). Compared with the historical period, the frequency of long drought duration, high drought severity, or intense drought events may be higher in the future under the SSP245 and SSP585 emission scenarios in the middle reaches of the Yellow River. The univariate return period is higher than the joint return period and lower than the concurrent return period, which can be used to estimate the univariate return period of the actual drought in the area using these two return periods.
This study is based on the Delta statistical downscaling approach, which performs well in trend feedback, but still has discrepancies in simulating the numerical values of the basin's annual and monthly data compared to the actual values. Future studies should combine different downscaling techniques, nesting regional climate models within global climate models, and using a combination of equally weighted average and non-equally weighted average ensemble methods to further reduce climate model uncertainty and improve simulation accuracy. In addition, this study only selected SPEI as the drought index, and future research should use multiple indicators to collectively assess drought and reduce the uncertainty associated with a single indicator. Furthermore, based on the existing two-dimensional drought research, further analysis of the joint distribution and return periods of the three-dimensional drought characteristic variables (D&S&I) would be of great importance for a deeper understanding of the impact of climate change on drought in the Yellow River Basin.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of water-2420773: “Evolution characteristics of meteorological drought under future climate change in the middle reaches of the Yellow River based on Copula function” By Zhang et al.
General comment:
This paper is focused on the investigation of drought characteristics in middle reaches of Yellow River Basin using observations and climate model outputs with some statistical methods. SPEI index was selected to describe the meteorological drought. It is an interesting paper which fits well the scope of the journal. Authors provided details of background in research topic and in methodology. They also provided some details in describing results. These are good in writing. Here I provide my concerns in Specific comment, which are minor points. I recommend minor revision at this stage.
Specific comment:
1. Line 6: author names should be listed as “Firstname (middle initial) Lastname”. Please check with the journal policies.
2. Line 42: “Introduction” should be “1. Introduction”. Please check with other sections following the journal policies.
3. Lines 55–57: At least a reference is needed to support this statement.
4. Lines 67–69: At least a reference is needed to support this statement.
5. Lines 129: This statement can be changed to “YRBM is selected as the research region in this study.”
6. Equations 1–2: Please specify Tem, Pre as temperature, precipitation, respectively. Eq 1 for temperature differs from eq 2 for precipitation, why is that? More explanations for eqs 1 and 2 are necessary so readers are easy to follow. In addition, a reference is needed to introduce Delta downscaling method.
7. Section 2.3.1: Please briefly discuss the potential shortcomings of Delta downscaling for this study.
8. Eq(3): Please specify w.
9. Line 240: Please specify “Di”, I guess it is short for “difference.”
10. Line 273–275: Please clarify drought intensity and drought severity.
11. Line 297: Please explain why to select five Copula functions.
12. Result section: It is somewhat difficult to follow without figures. Readers have to jump to and from between text and figures. Each figure should be put somewhere near its description.
13. Figures 2–4: Short description for each panel should be provided.
14. Figure 5: Unit for each panel (a–d) should be provided.
15. Figure 7 & 8: Please explain or define “experience frequency”, “theoretical frequency” and “empirical frequency” in figure caption. Is “empirical frequency” the same as “experience frequency”? Note that the “empirical frequency” does not appear in Figure 8.
16. Line 716: SPEI can be removed.
Some minor checks are needed.
Author Response
Reviewer #2
This paper is focused on the investigation of drought characteristics in middle reaches of Yellow River Basin using observations and climate model outputs with some statistical methods. SPEI index was selected to describe the meteorological drought. It is an interesting paper which fits well the scope of the journal. Authors provided details of background in research topic and in methodology. They also provided some details in describing results. These are good in writing. Here I provide my concerns in Specific comment, which are minor points. I recommend minor revision at this stage.
- Line 6: author names should be listed as “Firstname (middle initial) Lastname”. Please check with the journal policies.
A：Thank you,we had revised the author names.
- Line 42: “Introduction” should be “1. Introduction”. Please check with other sections following the journal policies.
A: We had revised them.
- Lines 55–57: At least a reference is needed to support this statement.
A: We had added the reference.
- Lines 67–69: At least a reference is needed to support this statement.
A: We had added the reference.
- Lines 129: This statement can be changed to “YRBM is selected as the research region in this study.”
A: we had revised the sentence.
- Equations 1–2: Please specify Tem, Pre as temperature, precipitation, respectively. Eq 1 for temperature differs from eq 2 for precipitation, why is that? More explanations for eqs 1 and 2 are necessary so readers are easy to follow. In addition, a reference is needed to introduce Delta downscaling method.
A: 1. we had revised the sentences as follow:
where, Temf (Pref) represent temperature (precipitation) after downscaling, Temobs_ref (Preobs_ref), represent the measured data of temperature (precipitation) in the reference period, TemGCMs_f (PreGCMs_f) represent GCMs data of temperature (precipitation) in the prediction period, TemGCMs_ref (PreGCMs_ref) represent GCMs data of temperature (precipitation) in the reference period.
2.we had added a reference.
- For the downscaling of temperature, we use the difference method. For downscaling of precipitation, we use the ratio method. Better results can be obtained by using different scaling methods for temperature and precipitation.
- Section 2.3.1: Please briefly discuss the potential shortcomings of Delta downscaling for this study.
A: Although delta downscaling method is simple and easy to operate, it requires high spatial resolution measured data as the basis, which limits the use of delta downscaling method to some extent.
- Eq(3): Please specify w.
A: ω, probabilistic weighted moment.
- Line 240: Please specify “Di”, I guess it is short for “difference.”
A: the difference between monthly precipitation and potential evapotranspiration (Di).
- Line 273–275: Please clarify drought intensity and drought severity.
A: we had revised sentences as follow: After obtaining the drought duration (D), drought severity (S, the sum of SPEI values in a drought events), and drought intensity (I, ratio of drought intensity to drought duration) of the middle reaches of the Yellow River using run theory.
- Line 297: Please explain why to select five Copula functions.
A: Because these are the five copula functions that are most commonly used. We have also included references here.
- Result section: It is somewhat difficult to follow without figures. Readers have to jump to and from between text and figures. Each figure should be put somewhere near its description.
A: We have adjusted some of the pictures. However, there are so many images in this article that only some of them can be presented as an appendix. Thank you for your advice.
- Figures 2–4: Short description for each panel should be provided.
A: a-e represents SPEI sequences on 1, 3, 6, 9, and 12 month timescales, respectively.
- Figure 5: Unit for each panel (a–d) should be provided.
A: (a), numbers of droughts; (b), drought duration; (c), drought severity; (d), drought intensity.
- Figure 7 & 8: Please explain or define “experience frequency”, “theoretical frequency” and “empirical frequency” in figure caption. Is “empirical frequency” the same as “experience frequency”? Note that the “empirical frequency” does not appear in Figure 8.
A: yes, empirical frequency”should be“experience frequency,we had revised it. The experience frequency refers to the frequency calculated by the experience frequency formula according to the measured sequence in order from large to small. Theoretical frequency refers to the frequency calculated by the preferred edge distribution function or copula function.
- Line 716: SPEI can be removed.
A: we had deleted the word.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for addressing my comments.
