Statistical Evaluation of the Influences of Precipitation and River Level Fluctuations on Groundwater in Yoshino River Basin, Japan

Round 1

Reviewer 1 Report

Title of the article:   Statistical Evaluation of the Correlations among Precipitation, 2 Groundwater and River Water Level Fluctuations in Yoshino 3 River basin, Japan

Kindly consider the here under-listed comments to be addressed with an appreciation of the authors' effort.

1. In the abstract, it would be better if the first sentence has revisited than just starting from the given method.
2. It would be better if consistency throughout the manuscript is checked and revisited accordingly specially spacing between reference citation bracket and text.
3. Citing Figure caption should be uniform throughout the document abbreviated.
4. The graphs in figure 4 is not visible and must be changed.
5. Texts within the table 3 are too small better if font size from author guide templates are followed.
6. Results implication should be discussed from the statistical approach points of view. Especially the correlation of main results discussion was missed.
7. The significance/implication of main findings of the study at abstract, introduction and conclusion has to be indicated though the paper is well organized with clear presentation.

 

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thanks very much for your reviewing and pertinent comments on our submitted manuscript. We have checked them carefully and find that the quality of our manuscript will be improved significantly if we revised the manuscript according to your suggestions.

The details of the responses to the comments and revisions can be checked as following.

 

Comment 1: In the abstract, it would be better if the first sentence has revisited than just starting from the given method.

Response: Thanks very much for your comment, and we absolutely agree with this comment. It will be better if we focus on the target instead of method.

Revision: Revise the first sentence as “Precise evaluation of the correlations among precipitation, groundwater and river water enhance our understanding on regional hydrological circulation and water resource management.”.

 

Comment 2: It would be better if consistency throughout the manuscript is checked and revisited accordingly specially spacing between reference citation bracket and text.

Response: Thanks very much for your comment, and we feel sorry to make this fault because of our careless.

Revision: We have checked carefully and add the spacing according to this comment.

 

Comment 3: Citing Figure caption should be uniform throughout the document abbreviated.

Response: Thanks very much for your comment, and we feel sorry to make this fault because of our careless.

Revisions: We have checked carefully and uniform the citing Figure caption according to this comment.

 

Comment 4: The graphs in figure 4 is not visible and must be changed.

Response: Thanks very much for your comment, and we make it not visible because it’s two large.

Revision: We have reedited this figure and make it looks better as following show in the word.

Comment 5: Texts within the table 3 are too small better if font size from author guide templates are followed.

Response: Thanks very much for your suggestion, and we checked the author guide templates carefully and find that the font size are definitely too small. Therefore we adjust the font size in all the Tables.

Revision: We have revised all the font size in the manuscript.

 

Comment 6: Results implication should be discussed from the statistical approach points of view. Especially the correlation of main results discussion was missed.

Response: Thanks very much for your comment, and we absolutely agree with this point. Actually, we have done some works in the aspects of correlations analyzing, however, the necessary discussion on this point is insufficient.

Revision: We have done some revisions in the parts of Results, as following.

Add “3.2. Correlations of hydrological processes” before “Table 2”.

Add ”To access the dependence of groundwater level on possible climatic and hydrological variables in the study area, the correlation coefficients between possible impact factors and aquifer water levels were calculated and shown in Table 2. The results show that the groundwater level in the study area show relative high negative correlations (absolute value above 0.24) with the barometric pressure and positive correlations (absolute value above 0.24) with precipitation, river water level, humidity and air temperature. Relative low correlations were detected between aquifer water levels and sunspot number, SST, indicating the solar activity and ENSO have weak influence on aquifer in the study area.” before “Table 2”.

 

Comment 7: The significance/implication of main findings of the study at abstract, introduction and conclusion has to be indicated though the paper is well organized with clear presentation

Response: Thanks very much for your comment, and we did ignore the expression of the significance and implications of main findings in this manuscript. Therefore, we advise the manuscript according to this comment.

Revision: We have done some revisions as following.

Revise the first sentence as “Precise evaluation of the correlations among precipitation, groundwater and river water enhance our understanding on regional hydrological circulation and water resource management.”.

Revise the last sentence in Paragraph 1 as “An analysis of aquifer responses to the possible influencing factors could improve our understanding of the regional water circulation and therefore guide water resource management [3].”.

Add “Evaluation and quantification on the variability of hydrological processes and their responses to related influencing factors provide guidance on regional water resources management.” in the last part of Introduction.

Add “The detailed information of correlations among precipitation, groundwater level and river water level provide an efficient implement to improve the regional water resource management efficiency.” In the last sentence of Paragraph 1 in Conclusion.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors:

The interactions between precipitation, river level and piezometric level have been extensively studied in the last decades through many methodologies. This manuscript proposes a methodology that, although not new, is very interesting to reveal the relationships between hydrological variables and thereby contribute to the field of water resource research.

The manuscript is well-written, and the explanations are generally clear. The narrative line is sound, and the methodology and results are generally presented in an explicit and clear way, what is always appreciated from the point of view of the reader.

However, in general terms, this reviewer considers that the work lacks a more rigorous hydrological approach, which considers and analyzes the influence of hydrological aspects such as the thickness of the saturated zone (very important when evaluating the delays between precipitation and the rise of the piezometric level), and others clearly related to the dynamics of groundwater (granulometry, total and effective porosity, field capacity, transmissivity, distance from the river, etc). The work presents a gap in this sense.

In addition, it is necessary for the authors to explain the prior treatment of the data that make up the time series processed using wavelet techniques. The errors in the input data, some of which are evident in the figures provided by the authors themselves, call into question the results obtained by applying these techniques.

I have highlighted and made comments on several specific aspects that should be improved before publication. You can find them in the revised pdf version.

 General comments

• The work would be enriched with a more exhaustive review of the state of the art on the applications of wavelet-based techniques to hydrogeology.
• Given the topic of the manuscript, the characterisation of the study area should provide further information on the climatic features and classification of the region. Similarly, the authors should improve the description of the aquifer by providing at least information on its geometry, regime (confined/unconfined), thickness, transmissivity, and storage coefficient. In addition, the authors have not mentioned if there are exploited wells/boreholes in the vicinity of the observation wells used in their study (in that case, the piezometric records might be affected by perturbances).
• The authors do not provide fundamental information in relation to the hydrological functioning of the basin. Are there dams or water diversions? What operating regime do the hydraulic works present? Is groundwater exploited? Does the river gauging station have an artificial channel or could it have been modified over time?
• Since the work is based on the treatment of time series of data, it is essential that the authors introduce a section in which they describe the process of debugging errors and completing the data series. There is evidence (figure 2) that the initial data present problems that should be solved before the mathematical treatment.
• The authors should justify why they consider these "impact factors" and not others more related to the dynamics of groundwater (granulometry, total and effective porosity, field capacity, transmissivity, distance from the river, etc). Really, the correlation between aquifer level and air humidity or air temperature cannot be expected to be significant.
• The overall text is well structured, however, the authors introduce concepts (such as the Clark´s method) and mention several gauging stations for the first time in the Results section, instead of Methodology section.
• Some of the wavelet analysis methods applied are barely described. The manuscript would benefit from a couple of lines explaining the rationale/purpose of each method and the reason of the choice.
• The authors should enlarge and improve the quality/resolution of several figures that are currently difficult to read and interpret and also add labels to figures that include several graphs.
• There are a few spelling and format mistakes to be corrected, which have been highlighted throughout the text.

Please, find these comments and several additional suggestions indicated in the revised version of the manuscript attached.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thanks very much for your time consumption on our submitted manuscript, and also for your pertinent evaluation on the scientific significance and writing organization of this paper. Generally speaking, most of the comments are pertinent and can be used to improve the quality of the paper. And the lacks of the influence of hydrological aspects on dynamics of groundwater, and the prior treatment of the data before wavelet analysis should be noticed during the process of revising.

Responses and revisions according to the general and specific comments as listed as follows.

 

General comment 1: The work would be enriched with a more exhaustive review of the state of the art on the applications of wavelet-based techniques to hydrogeology.

Response: Thanks very much for your comment, and we absolutely agree with this point. The review of the applications of wavelet-based techniques to hydrogeology can improve the understanding on the implications of this paper.

Revision: revise the 3^rd paragraph as follows.

Most previous studies employed spectral analysis to identify the aquifer responses to possible influent factors, such as precipitation variability [9], tidal effects [10,11] and lake level fluctuations [12]. A spectral analysis can be used to evaluate the coherence and phase lag between external hydrological processes and groundwater-level responses in the frequency domains, and to estimate the degree of influence and travel time of external stresses to aquifers. However, a spectral analysis only determines the frequency content of aquifer water levels. Temporal variation in the groundwater-level response to influent factors can be evaluated using a wavelet analysis [13]. The impact of climate and anthropic effects on aquifers has been studied using a wavelet analysis in many parts of the world [3,6,14]. The wavelet analysis can not only evaluate the variability of aquifer in different spatial and temporal frequencies using signal amplification function, but also analyze the interaction between possible factors and groundwater using coherence and cross-spectrum functions. The aquifer’s teleconnecion with climate indices (ENSO index, NAO index, et al.), the interaction with local climate variations (precipitation, air temperature, barometric pressure, et al.), and the responses to external stresses (tidal effect, pumping, et al.) can be assessed based on wavelet techniques. And the impact of climate and anthropic pressures on groundwater resource can be evaluated to improve the understanding on water resource management. However, the systematic analyses on the interaction between precipitation, river water and groundwater from short-term to long-term time scaleshave not been assessed.

 

General comment 2: Given the topic of the manuscript, the characterisation of the study area should provide further information on the climatic features and classification of the region. Similarly, the authors should improve the description of the aquifer by providing at least information on its geometry, regime (confined/unconfined), thickness, transmissivity, and storage coefficient. In addition, the authors have not mentioned if there are exploited wells/boreholes in the vicinity of the observation wells used in their study (in that case, the piezometric records might be affected by perturbances).

General comment 3: The authors do not provide fundamental information in relation to the hydrological functioning of the basin. Are there dams or water diversions? What operating regime do the hydraulic works present? Is groundwater exploited? Does the river gauging station have an artificial channel or could it have been modified over time?

Response: Thanks very much for your comment, we absolutely agree with these two points. And we ensured that the quality of this manuscript can be improved significantly if the information of climatic features, region classification, aquifer description and other background were provided.

Revision: revise the part of “2.1 study area and datum” as follows.

The study area is located in the lower Yoshino catchment in south Japan (Figure 1). The Yoshino River is 194 km in length and has a watershed of 3,750 km2. The study area is a watershed with the area of about 840 km² located in Tokushima Plain. The plain is consisted of alluvial delta clay and sand, and about 75% of the study area is covered by forests and meadow. The elevation of the investigated watershed decreases from west to east and ranges from -10 to 185 m. The mean annual precipitation from 1892 to 2014 at the Tokushima meteorological station is about 1,650 mm per year, and the average annual air temperature from 1890 to 2014 is about 15.5°C. A national meteorological station, hydrological station and four observation wells are located along the Yoshino River.

The data used in the analysis of precipitation, groundwater levels and river water levels consisted of 43 years (from 1972 to 2014) of daily data. Daily precipitation was recorded by an automatic rain gauge installed at the Tokushima meteorological station. The groundwater level (with reference to the annual mean sea level in Tokyo Bay) was observed using pressure water level gauges installed in the observation wells. The study aquifer is composed of silt, sand and gravel. The screens of the observation wells were positioned at depths of 2 to 10 m, and therefore the study considered the groundwater present in the unconfined aquifer in the study area. The transimissivity of the unconfined aquifer is investigated and calculated as about 1000 m²/day in the study area. No artificial exploitation was detected in the study area, and the aquifer water levels were inferred to be disturbed slightly by human activity. No dams or water diversions were built in the upper reaches. The river water level was measured by a bubble type water gauge installed in the hydrological station and no artificial channels were found in the station.

 

General comment 4: Since the work is based on the treatment of time series of data, it is essential that the authors introduce a section in which they describe the process of debugging errors and completing the data series. There is evidence (figure 2) that the initial data present problems that should be solved before the mathematical treatment.

Response: Thanks very much for your comment, and we absolutely agree with this point. Also, we have done some preprocessing works before the mathematical treatment.

Revision: we make the revisions of the 3^rd paragraph in Part 2.1 as follows.

A time series of precipitation and aquifer water levels in observation wells 1 to 4 and the river water level are presented in Figures 2(a)–2(f), respectively. Figure 2 shows that the daily precipitation, groundwater levels and river water levels fluctuated periodically. Figure 2(c) shows the aquifer water levels in well 2 suddenly changed in 2004, which was associated with a shift in the measurement location, and the aquifer water levels after 2004 were adjusted for consistence. There were several water level measurements missing during 1976 and 1978 for well 4. An interpolation process was used to resolve this problem in the subsequent analysis. The time series were standardized before subsequent analyses.

 

General comment 5: The authors should justify why they consider these "impact factors" and not others more related to the dynamics of groundwater (granulometry, total and effective porosity, field capacity, transmissivity, distance from the river, etc). Really, the correlation between aquifer level and air humidity or air temperature cannot be expected to be significant.

Response: Thanks very much for your comment, and we absolutely agree with this point. Actually, the influencing of possible factors on aquifers and other hydrological processes are very complex, it’s very difficult to access the impacts of the possible factors related to the dynamics of groundwater with limited data. Also, the main object of this paper focuses on the inter-annual variations, which might be associated with the influences of the climatic factors.

 

Revision: we make the revisions of the 3^rd paragraph in Part 3.2 as follows.

To access the dependence of groundwater level on possible climatic and hydrological variables in the study area, the correlation coefficients between possible impact factors and aquifer water levels were calculated and shown in Table 2. The results show that the groundwater level in the study area show relative high negative correlations (absolute value above 0.24) with the barometric pressure and positive correlations (absolute value above 0.24) with precipitation, river water level, humidity and air temperature. However, the high correlation with the humidity and air temperature might be explained by the synchronous seasonal variation feature instead of interaction. Relative low correlations were detected between aquifer water levels and sunspot number, SST, indicating the solar activity and ENSO have weak influence on aquifer in the study area.

 

General comment 6: The overall text is well structured, however, the authors introduce concepts (such as the Clark´s method) and mention several gauging stations for the first time in the Results section, instead of Methodology section.

Response: thanks very much for your comment, and we absolutely agree with this point.

Revision: we have do the revisions of the part 4.2 as following.

Precipitation recharge to aquifer occurs with lags that can range from hours to days, and even months [12]. The recharge-water travel time in the study area was estimated from the pattern of the arrows in the precipitation-groundwater WTC at the inter-annual time scale (Figure 8). The results were consistent for each observation well in the study area. The results of the correlation between precipitation and groundwater in the different spatial and temporal domains indicated that the daily precipitation affected the groundwater at periodicities of 4–16 and 32–64 days during July and September in the study area. In 2013, the area of significant coherence with periodicities of 4–16 days had an in-phasing of about 1/8 of a cycle, suggesting a 1 day delay in the response of the aquifer to precipitation. The phase difference in the periodicities of 32–64 days equated to zero, and this pattern indicated no time lag existed at these time scales. In 2014, the arrow angles with significant coherence in the periodicities of 4–16 days ranged from -1/3 to -2/3 π, which indicated that the response time of the aquifer to precipitation was about 3–6 days. An in-phasing of about 5/6 of a cycle was detected in the periodicities of 32–64 days, indicating a time lag of about 40 days.

The precipitation led aquifer water levels by up to 6 days in the study area, which differed from other examples of semi-confined aquifers published in the literature [3,6]. This might be a result of the unconfined condition of the study aquifer. The different time lags of groundwater level to precipitation, with periodicities of 4–16 days during 2013 and 2014, might be due to the timing of maximum precipitation. The groundwater levels in the unconfined aquifer responded quickly to the variation in precipitation when the soil pores were not filled. The maximum precipitation occurred in late August in 2013 and early August in 2014, and this behaviour might cause a longer average travel time of precipitation to the aquifer in 2014. The time lags with periodicities of 32–64 days might be associated with other local climatic indices, such as barometric pressure, humidity and air temperature [3].   

 

General comment 7: Some of the wavelet analysis methods applied are barely described. The manuscript would benefit from a couple of lines explaining the rationale/purpose of each method and the reason of the choice.

Response: thanks very much for your comment, and we absolutely agree with this point. Actually, we consume too much attention in the explanation of calculation procedures instead of the reason of the choice.

Revision: we rewrite Part 2.2 as follows.

The multiresolution analysis and continuous wavelet analysis approaches were applied in this study. First, wavelet decomposition was implemented to extract aquifer water levels and their possible impact factors across different resolution levels, and the standard deviation (SD) was calculated to quantify the multiresolution levels. Then, a cross-correlation between aquifer water levels and potential impact variables across different levels was conducted to reveal the dependence of aquifer water level on the possible influencing factors. Finally, a wavelet analysis was performed to quantify the temporal features in different periods of precipitation, and aquifer and river water levels. A wavelet coherence (WTC) analysis was applied to detect the aquifer responses to precipitation and river water levels in both the time and frequency domains.

A multiresolution analysis can be applied to decompose a time series into a series of successive approximations and details in increasing order of resolution to study signals at different resolutions [14]. Wavelet decomposition returns the wavelet coefficients of the signal at different levels through the implementation of specific wavelets. Wavelet decomposition is performed based on designed signal filters [3]. The details of the algorithm can be referred to the paper by Mallat [15].

To quantify the relationship between two signals at different resolution levels, a multiresolution cross-analysis [14] was applied. Cross-correlation evaluates the similarity of two time series as a function of the lag of one series in relation to the other. The cross-correlation function (CCF) analysis was applied to identify the influence of possible factors on aquifer water levels in different frequency domains. The cacluation of the CCF is described by Charlier [14].

A wavelet analysis assesses the variation of a signal in both the temporal and frequency domains [13]. In the field of hydrology, this technique is applied in two aspects: to determine the spatial and temporal variation of hydrological factors, including precipitation, river discharge and aquifer water levels [16–19]; and to quantify the interaction between hydrological variations and climatic indices, such as solar activity [11,20], the North Atlantic Oscillation [6,21], and the ENSO [20,22].

The wavelet techniques utilized in this study included the wavelet power spectrum (WPS) and WTC. The WPS represents the magnitude of the variance in a time series at a given frequency and location in time. This technique provides an effective approach to analyze the variability of hydrological processes. The WPS [23] is defined as the square absolute value (or square amplitude) of the wavelet transform coefficients .

To eliminate the distortion of a wavelet analysis in time-frequency domains, the concept of the cone of influence (COI) was introduced, in which the e-folding time function is used to overcome edge effects [23]. The edge effects are negligible for wavelet spectra located in the COI region. The statistical significance of wavelet power can be assessed relative to the null hypothesis that the signal is generated by a stationary process with a given background power spectrum. A significance test was conducted using the Monte Carlo method [23]and a 5% significance level was adopted.

The WPS enables the degree of complexity of a simplex signal to be characterised. To assess the relationship between two signals in the time-frequency domains, a cross-wavelet analysis should be introduced [13]. The WTC can determine a significant coherence even though the common power is low [24]. Concerning hydrological issues, this approach has been used to access the influence of ENSO on stream flow [22], construct models to forecast river flow [25] and evaluate timing errors in hydrological predictions[26].

The significance contour for the cross-wavelet analysis can be found using the chi-squared distribution, with details of the algorithm provided by Torrence and Compo [23]. The 5% significance level was considered in this paper. The details of the involved wavelet techniques in this study are described in the relevant references [17, 23, 24, 27]. All subsequent computations and analyses were conducted within the MATLAB environment.

 

General comment 8: The authors should enlarge and improve the quality/resolution of several figures that are currently difficult to read and interpret and also add labels to figures that include several graphs.

Response: Thanks very much for your comment, and we absolutely agree with this point.

Revision: Figure 4 was revised as following in the word.

General comment 9: There are a few spelling and format mistakes to be corrected, which have been highlighted throughout the text.

Response: Thanks very much for your comment, and we should make corrections according to your suggestion

Revision: Please check in the revised manuscript.

 

Specific comment: Please, find these comments and several additional suggestions indicated in the revised version of the manuscript attached.

Response: Thanks very much for your comment, and the quality can be improved if we make the corrections according to your specific comment.

Revision: The details can be checked in the revised manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear authors:

In my opinion, despite the modifications introduced in the manuscript, the work still has the severe deficiencies that were pointed out in the previous revision.

Just to illustrate one of them, I could mention that the basin, in fact, is regulated by a large dam (geographical coordinates: 34º2.010´N, 133º 48.36´E), which is located upstream the gauging station. The authors have not considered this aspect, what invalidates any cross-analysis between precipitacion, river level and groundwater level. In addition, the authors are not considering the existing population (more than 300.000 people with a demand greater that 50 hm³/year), which evidently, alters the natural regime of the basin.

I still think that the hydrological series used in this work present severe deficiencies that call the results into question.

 

Author Response

Dear Reviewer,

Thanks very much for your reviewing and suggestion on the resubmitted manuscript. We feel really sorry that our previous revised manuscript can’t meet your requirement, especially in the aspects of consideration of artificial influences (large dams, artificial water usage) on natural hydrological regime. We absolute agree with your viewpoint that the large dam regulation and artificial water usage can alter the natural hydrological processes, and consequently have potential effects on the seasonal and daily variations. And we also recognize that the lack of description on larges dams and populations in the basins make the data analysis in this manuscript existing problems.

However, we still think the data analysis results can still make sense because of the following: the targets of this manuscript mainly emphasize on the influences of precipitation/river water on groundwater in the study area. The artificial water usage in the basin mainly occurs in the Ikeda Dam and Daiju-weir Dam, and it might have effects on the river water levels in the basin. And the possible interaction between river water and aquifer were analyzed based on observed data, and this interaction can be analyzed even if the observed river water level was affected artificially.

Therefore, for better understanding on the objective of this manuscript, main revisions were made as following: (1) modify the objective as the influence of precipitation/river water on aquifer instead of Evaluation of the Correlations among Precipitation, Groundwater and River level Fluctuations. Actually, the influence of precipitation on river water is not considered in this paper. (2) add the description of possible artificial influences on hydrological processes in the investigated basin and the explanation of how to reduce the influences in the manuscript. The revisions according to this point can be reviewed in yellow highlight in the revised manuscript.  

  

Thanks again for your help!

 

Best regards!

Author Response File: Author Response.docx