Tendency of Runoff and Sediment Variety and Multiple Time Scale Wavelet Analysis in Hongze Lake during 1975–2015
Round 1
Reviewer 1 Report
Dear Authors,
Please find my comments in the attached file.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments
Point 1: (Abstract) What is the river construction?
Response 1: It stands for the hydraulic engineering projects.
The revised statement is as follows:
“changes in heavy rainfalls pattern, the construction of hydraulic engineering projects and LUCC are the main reasons for the significant decrease and mutation variation of inflow sediment.”
Point 2: (2.2.1) Justify with reference, please.
Response 2: We have cited references in the manuscript.
Point 3: (2.2.2) Justify with reference, please.
Response 3: We have cited references in the manuscript.
Point 4: (2.3.1) Why you apply only this type of wavelet? Please explain it bit more with references.
Response 4: We have explained it in the manuscript.
The revised statement is as follows:
“At present, many wavelet functions can be used [44], for example, Mexican hat wavelet, Haar wavelet, Morlet wavelet, and Meyer wavelet. Among, the Morlet wavelet is widely used to identify periodic oscillations of the real life signals, which can detect the time-dependent amplitude and phase for different frequencies [45-46], it is a very accurate method for obtaining the periodicity [47]. Given the hydrological characteristics of the runoff and sediment time series, a continuous wavelet transform should be used to detect the existence of oscillations and their period, so the research selected Morlet wavelet function to analyze the multi-time scale variations of the runoff and sediment time series in Hongze Lake.”
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear Authors,
thank you very much for this interesting work,
in case that the Editor asks for a revised version of the manuscript,
i am to serve as reviewer of the revised version
Kind Regards,
Reviewer
Author Response
Response to Reviewer 2 Comments
Dear Reviewer,
Thanks for your notice.
Our manuscript has been revised according to the reviewers’ comments carefully.
The corrections have been marked in the manuscript.
Your insightful and professional comments will help to improve the manuscript.
Kind Regards,
Yu Duan
Author Response File: Author Response.docx
Reviewer 3 Report
A BRIEF SUMMARY
The paper titled “Tendency of runoff and sediment variety and multiple time scale wavelet analysis in Hongze Lake during 1975-2015” presents an interesting topic for readers of this Journal. The topic represents a line of research very interesting. This paper proposes a combinatorial mutation test method with high precision to analyze the trend of runoff and sediment time series of Hongze Lake 442 from 1975 to 2015.
This topic is interesting for the researchers in the field of hydrology. For this reason I suggest that the authors try to add some more references especially in the "part 1 (introduction)" of the paper. I have indicated suggestion for this, but more can be added which would make the foundation for the arguments stronger.
In the meantime I think that the authors should take into account some comments that follow, which, to my opinion, will improve the work. In the follow the specific comments.
SPECIFIC COMMENTS
Paragraph 1 (INTRODUCTION). In my opinion the manuscript can be upgraded detail justifying the importance of this case study. My question is: Which aspects have you take into account to define the case study?
Paragraph 1 (INTRODUCTION). It's advised to add some references. I suggest you, as example, the following work. The authors in my opinion have to add more references relating to the influence of land use change on flooding.
- Apollonio, C.; Balacco, G.; Novelli, A.; Tarantino, E.; Piccinni, A.F. “Land Use Change Impact on Flooding Areas: The Case Study of Cervaro Basin (Italy)”. Sustainability 2016, 8, 996. https://doi.org/10.3390/su8100996
Paragraph 3.3.2 (Trend variation of sediment and cause analysis of catastrophe point). Why the authors don’t provide a Risk Curve to identify a “catastrophe point”? Several study, on this topic, provide similar curve.
It’s advised a language review.
Author Response
Response to Reviewer 3 Comments
Point 1: Paragraph 1 (INTRODUCTION). In my opinion, the manuscript can be upgraded detail justifying the importance of this case study. My question is: Which aspects have you take into account to define the case study?
Response 1: The purpose of this research is to improve the accuracy of the trend detection technology of time series, then clarify the variation trend, change points and periodicity of the runoff and sediment time series of the Hongze Lake, and further analyze the influencing factors from climate variability and anthropogenic activities. In this paper, the hydrologic stations of the surrounding water system of Hongze Lake are selected to explore the variation trend，change point and periodicity of runoff and sediment flowing into and out of the Hongze Lake basin from 1975 to 2015. A combinatorial mutation test method based on the M-K test and Pettitt test is proposed to identify the change points. Based on statistical analysis, wavelet analysis is used to analyze the spatiotemporal variation characteristics of the hydrological time series, then predict its variation trend in a short time in the future. By analyzing the causes of the change point, revealing the impacts of climate variability and anthropogenic activities on runoff and sediment variations in Hongze Lake. It is of great significance for the management and economic development to understand the characteristics, variation trends and influencing factors of runoff and sediment in Hongze Lake scientifically.
Point 2: Paragraph 1 (INTRODUCTION). It's advised to add some references. I suggest you, as example, the following work. The authors in my opinion have to add more references relating to the influence of land use change on flooding.
Response 2: We have referred to more references, which made the foundation for the arguments stronger. The influence of LUCC also be added into the introduction, and the manuscript cited the reference you provided, it is an interesting article.
The revised statement is as follows:
“Also, the research on the influence of climate variability and anthropogenic activities on water circulation and water resources is a hot topic in climatology and hydrology. In recent years, extreme weather events such as a rainstorm, flood, strong storm surge, drought, high temperature and heat wave have become more and more intense [31-32]. Climate variability, mainly characterized by global warming, affects the regional land water circulation by changing the atmospheric temperature and precipitation, and drives the changes of hydrological factors such as runoff and sediment [33-34]. Anthropogenic activities mainly include the construction of hydraulic engineering, water and soil conservation measures, unreasonable farming, etc., of which the construction of hydraulic engineering is a typical representative, sediment is trapped in the reservoir, resulting in reduced sediment transport downstream of the river [35]. As an artificial “disturbance system”, land use/cover change (LUCC) is not only an important part of regional environmental evolution, but also one of the main causes of physical process changes on the surface[36-37]. Ervinia et al. [38] found that land use change enhanced the impact of climate change on runoff change. Dao et al. [39] found that climate change from 1978 to 2000 had a stronger impact on the hydrological process of the Vietnam river basin than land use change. Apollonio et al.[40] showed the impact of land use on the hydrological response is closely related to the watershed scale. Bussi et al. [41] simulated the effects of future climate and land use changes on the transport of suspended sediment in the Thames River.”
Point 3: Paragraph 3.3.2 (Trend variation of sediment and cause analysis of catastrophe point). Why the authors don’t provide a Risk Curve to identify a “catastrophe point”? Several study, on this topic, provide similar curve.
Response 3: We have provided the curves to identify the change point of the sediment time series, as shown in Figure 11, which can better explain the causes of sediment abrupt changes.
Point 4: It’s advised a language review.
Response 4: We have reviewed the manuscript, and asked someone to check the English language.
Author Response File: Author Response.docx
Reviewer 4 Report
The review of the paper
“Tendency of runoff and sediment variety and multiple time scale wavelet analysis in Hongze Lake during 1975-2015”
by Yu Duan et al.
I found the paper generally well prepared. The topic of this work (climate changes, trend analysis) is quite common and lack of novelty seems to be one of the weaknesses of the work. However, on the other hand, presented work provides important information for local community and therefore is valuable. In my opinion, before publication (of course, the final decision will be taken by the Editor) some issues should be clarified, therefore revision is needed.
Please, express the novelty of the study in the Paragraph “Introduction” more precisely. What is new in this study? What do you introduce to the scientific society?
the term “catastrophe point” - I do not negate it, but the term "change point" is used much more often, and it is also unambiguous for the reader.
Line 18-21: “Then the time series….” this sentence is too long and therefore difficult to understand.
Figure 1 is blurred, its quality should be improved.
Line 208-209: “…. with the obvious characteristics of more runoff and more sediment, less runoff and less sediment. “ I am sure you can express this statement in a more sophisticated way.
Table 1 – inspection criterion: the interval −1.96 ≤ Z ≤ 1.96 seems to be a more exact way of presentation than absolute value
Line 391: X and Y should be explained
Line 393: “The actual annual average inflow runoff…”: not clear, do you mean measured inflow?
Line 395-396: “…decrease in rainfall accounted for 28%, and the increase in water use for human activities accounted for 73%.” How this values were estimated?
Line 398: “The M-K trend test shows that the statistic Z=4.72 ….” this value does not appear above in the text.
Line 412: “The results show that anthropogenic activities have a great influence on sediment transport except for rainfall and runoff” - unclear
Line 407-439: what about land use changes and changes in heavy rainfalls pattern over the period 1975-2015? Do they contribute to the change in sediment yield?
Author Response
Response to Reviewer 4 Comments
Point 1: Please, express the novelty of the study in the Paragraph “Introduction” more precisely. What is new in this study? What do you introduce to the scientific society?
Response 1: The purpose of this research is to improve the accuracy of the trend detection technology of time series, then clarify the variation trend, change points and periodicity of the runoff and sediment time series of the Hongze Lake, and further analyze the influencing factors from climate variability and anthropogenic activities. In this paper, the hydrologic stations of the surrounding water system of Hongze Lake are selected to explore the variation trend，change point and periodicity of runoff and sediment flowing into and out of the Hongze Lake basin from 1975 to 2015. A combinatorial mutation test method based on the M-K test and Pettitt test is proposed to identify the change points. Based on statistical analysis, wavelet analysis is used to analyze the spatiotemporal variation characteristics of the hydrological time series, then predict its variation trend in a short time in the future. By analyzing the causes of the change point, revealing the impacts of climate variability and anthropogenic activities on runoff and sediment variations in Hongze Lake. It is of great significance for the management and economic development to understand the characteristics, variation trends and influencing factors of runoff and sediment in Hongze Lake scientifically.
Point 2: the term “catastrophe point” - I do not negate it, but the term "change point" is used much more often, and it is also unambiguous for the reader.
Response 2: The “catastrophe point” in the manuscript were replaced by “change point”.
Point 3: Line 18-21: “Then the time series….” this sentence is too long and therefore difficult to understand.
Response 3: The sentence was reedited in the manuscript, which made it easy to understand. The revised statement is as follows:
“Then the runoff and sediment time series analyzed by the wavelet method, the results showed that the time series has multi-time scale characteristics. The annual inflow runoff and sediment would enter into the dry period after 2015, and both would be in the valley floor stage.”
Point 4: Figure 1 is blurred, its quality should be improved.
Response 4: We have inserted a higher resolution image into the manuscript, as shown in Figure 1.
Point 5: Line 208-209: “…. with the obvious characteristics of more runoff and more sediment, less runoff and less sediment. “ I am sure you can express this statement in a more sophisticated way.
Response 5: We have modified the statement to make it more professional.
The revised statement is as follows:
“The variation of runoff and sediment is closely related, it means that the sediment increases with the runoff, and when the runoff decreases, the sediment will be decreased at the same time.”
Point 6: Table 1 – inspection criterion: the interval −1.96 ≤ Z ≤ 1.96 seems to be a more exact way of presentation than absolute value
Response 6: “|Z|≤1.96” in Table 1 were replaced by “-1.96≤Z≤1.96”.
Point 7: Line 391: X and Y should be explained
Response 7: In the manuscript, X is for rainfall, Y is for inflow runoff.
The revised statement is as follows:
“According to the regression analysis [51], the relationship between inflow runoff Y and rainfall X in the base period is:”
Point 8: Line 393: “The actual annual average inflow runoff…”: not clear, do you mean measured inflow?
Response 8: It means the measured inflow.
The revised statement is as follows:
“The measured annual average inflow runoff is 27.10 billion m3 during 1993-2015, ”
Point 9: Line 395-396: “…decrease in rainfall accounted for 28%, and the increase in water use for human activities accounted for 73%.” How this values were estimated?
Response 9: I’m very sorry for the writing errors in the manuscript, which caused trouble in readers. In our research, “73%” should be replaced by “72%”.
In the manuscript, the main factors affecting the runoff are climate variability and anthropogenic activities, and in the study area, climate variability is mainly reflected in rainfall changes. According to the rainfall-runoff relationship, the average annual inflow runoff is 32.75 billion m3 during 1993-2015, the runoff decreased by 1.09 billion m3 compared with 1975-1993. The measured annual average inflow runoff is 27.10 billion m3 during 1993-2015, so in fact, the runoff decreases by 3.92 billion m3 compared with 1975-1993. So the decrease in rainfall accounted for 28% (1.09/3.92*100%=28%), the human activities accounted for 72% (1-28%=72%).
Point 10: Line 398: “The M-K trend test shows that the statistic Z=4.72 ….” this value does not appear above in the text.
Response 10: In our research, we also done the work of M-K trend analysis for the water consumption time series, the results showed that the statistic Z=4.72.
The revised statement is as follows:
“M-K trend analysis was conducted on the water consumption time series, the results showed that the statistic Z=4.72 is far more than 95% significant level”
Point 11: Line 412: “The results show that anthropogenic activities have a great influence on sediment transport except for rainfall and runoff” - unclear
Response 11: In response to this question, we did further research, and a more accurate conclusion was summarized.
The revised statement is as follows:
“Sediment transport is mainly related to climate variability and anthropogenic activities in the basin. In the trend analysis, the variation trend of sediment flowing into and out of Hongze Lake are related to runoff. The M-K test statistics of rainfall and runoff in the study period did not exceed the significance level, while the sediment exceeded the significance level and showed a more obvious decreasing trend. It meant that, rainfall and runoff had no obvious effects on the decreasing trend of sediment, anthropogenic activities may had a great influence on sediment transport.”
Point 12: Line 407-439: what about land use changes and changes in heavy rainfalls pattern over the period 1975-2015? Do they contribute to the change in sediment yield?
Response 12: We supplemented the research of land use changes and changes in heavy rainfalls pattern over the period 1975-2015, we found that they did have an impact on sediment change in the basin.
The revised statement is as follows:
“According to the above study, the change point of sediment flowing into and out of Hongze Lake occurred in 1991. In terms of climate variability, although there was no significant change in rainfalls from 1975-2015, but heavy rainfalls affect the variation of runoff and sediment in a short time. For example, in 1991, the average rainfall of the Huaihe River was 1082 mm, 20% more than the average year. The rainfall is concentrated from June to August, then the runoff and sediment flowing into Hongze Lake increased significantly, and the largest value occurred in July. While after 1991, the rainfall decreased and the M-K test statistic of rainfall is -0.37<0 during 1991-2015, which showed that the rainfall decreased after 1991, so the rainfall reinforced the decreasing trend of sediment.
In terms of anthropogenic activities, LUCC in the Huaihe River can result in alterations in rainfall–sediment yield relationship [53]. According to statistics, anthropogenic activities strongly disturbed the surface of the Huaihe River basin, causing the changes of land use in the region. Before the 1980s, the Huaihe River basin was dominated by cultivated land and forest. With the increase of the regional population, more natural wetlands and forest are transformed into construction land and farmland, water and soil erosion in the basin is becoming more and more serious, the ecological environment of the river basin is seriously damaged. Since the 1980s, the government has started soil and water conservation work in the basin, focusing on reducing sloping farmland, increasing vegetation, and closing mountains for forest and grass, thus controlling soil erosion to a certain extent. These anthropogenic activities have changed the land use and cover of the study area, thus causing the decrease of runoff and sediment to some extent. In addition, hydraulic engineering projects played an important role to decrease the sediment, due to the series flood disaster in the Huaihe River basin, China has designed 19 projects to control the Huaihe River flood, by 1998 (when the Shimantan reservoir was completed), the upstream reservoir of Hongze Lake had increased by 0.77 billion m3, part of the sediment was intercepted by the reservoir. At the same time, the implementation of the projects to control the Huaihe River is beneficial to soil and water conservation, since 1991, the upstream of Hongze Lake has been treated with 2184 km2 of soil erosion.
So, the climate variability and anthropogenic activities have a significant impact on the sediment flowing into and out of Hongze Lake, changes in heavy rainfalls pattern, the construction of hydraulic engineering projects and LUCC are the main factors.”
Author Response File: Author Response.docx
Round 2
Reviewer 4 Report
I am very thankful for all the answers and much effort given by the authors to correct the text. I am satisfied with all submitted explanations.
