Determination of Seasonal Indices for the Regionalization of Low Flows in the Upper Vistula River Basin
Round 1
Reviewer 1 Report
Dear Authors,
Your manuscript is well written. Your manuscript is written in accordance with the requirements (followed structure, formulas are written in the right section, high quality of figures, etc.)
However, I recommend shortening the conclusions. Think about the fact that the conclusions are logically related to the purpose of the work.
Also, note that you have used very little new scientific literature (in the last 5 years).
Author Response
The Authors would like to sincerely thank for reviewing the manuscript. We greatly appreciate the Reviewer for the constructive comments and suggestions. Please find below our point-by-point responses to those concerns. All changes were marked in colour in the manuscript. We hope that our responses will be satisfactory.
Reviewer comment: Your manuscript is well written. Your manuscript is written in accordance with the requirements (followed structure, formulas are written in the right section, high quality of figures, etc.)
However, I recommend shortening the conclusions. Think about the fact that the conclusions are logically related to the purpose of the work.
Also, note that you have used very little new scientific literature (in the last 5 years).
Authors’ answer: We sincerely thank Reviewer for the nice and complimentary words about our manuscript. We agree with Reviewer and shortened the conclusion and we expanded the introduction by adding 8 recent literature references:
Brunner, M. I.; Tallaksen, L. M. Proneness of European catchments to multiyear streamflow droughts. Water Resources Research, 2019, 55, 8881–8894. DOI: https://doi.org/10.1029/2019WR025903.
Floriancic, M. G.; Berghuijs, W. R.; Molnar, P.; Kirchner, J. W. Seasonality and drivers of low flows across Europe and the United States. Water Resources Research, 2021, 57, e2019WR026928. DOI: https://doi. org/10.1029/2019WR026928.Również, zgodnie z sugestią
Dierauer, J. R.; Whitfield, P. H.; Allen, D. M. Climate controls on runoff and low flows in mountain catchments of western North America. Water Resources Research, 2018, 54(10), 7495–7510. DOI: https://doi.org/10.1029/2018WR023087
Serrano, L.; Ribeiro, R.B.; Borges, A.C.; Pruski, F.F. Low-Flow Seasonality and Effects on Water Availability throughout the River Network. Water Resour. Manag. 2020, 34, 1289–1304. DOI: https://doi.org/10.1007/s11269-020-02499-3.
Vlach, V.; Ledvinka, O.; Matouskova, M. Changing Low Flow and Streamflow Drought Seasonality in Central European Headwaters Water, 2020, 12, 3575. DOI: https://doi.org/10.3390/w12123575.
Laaha, G. A mixed distribution approach for low-flow frequency analysis –Part 1: concept, performance and effect of seasonality. Hydrology and Earth System Science, Discussions, 2022, DOI: https://doi.org/10.5194/hess-2022-195.
Pournasiri, P. M.; Pal, I.; Lall, U.; Naveau, P.;Towler, E. Variability patterns of the annual frequency and timing of low streamflow days across the United States and their linkage to regional and large-scale climate. Hydrological Processes, 2019, 33(11). DOI: 1569–1578. https://doi.org/10.1002/hyp.13422.
Fangmann, A.; Haberlandt, U. Statistical approaches for identification of low-flow drivers: Temporal aspects. Hydrology and Earth System Sciences, 2019, 23(1), 447–463. DOI: https://doi.org/10.5194/hess-23-447-2019.
Reviewer 2 Report
The paper makes the observation that reliable estimation of low flow hydrology is key to successful water management in Poland and other countries particularly for small, rural water supply systems. The study analyses 12 seasonality indices for the regionalization of low-flow characteristics in the Upper Vistula River Basin in Poland. The paper should be of interest to readers of the journal since, as the authors state, many communities rely on diversions from watercourses in natural catchments.
The paper is largely well written with some significant grammatical errors in the introductory sections. These issues can be largely addressed with improvements in grammar and improved explanation of concepts. There is a certain amount of repetition in the introductory section which should be streamlined.
The review of literature cites an adequate number of relevant papers however very few of the papers cited are current - the majority are papers from the 1970's and 1980's. The majority are references to Polish publications. I would like to see more recent publications cited and a broader inclusion of papers on relevant topics from other countries.
The authors use the term uncontrolled catchments throughout. the flow may be uncontrolled draining from a catchment but there is no such thing as an uncontrolled catchment. These and similar grammatical errors have been highlighted in the attached review copy of the manuscript and need to be addressed.
The modeling section is weak and requires better explanation and improved discussion of certain parameters. It isn't clear to the reader what months comprise a winter versus a summer flow regime - these need to be better defined. Since this section is critical to the sections that follow the authors need to pay special attention to attending to this section of the paper.
The conclusions section is good but could do more to speculate on the potential applications of the study and in particular how this data may be used. The authors cite applications without any details of how the information might be used to inform decision making. this would be a useful addition.
Comments for author File: 
Comments.pdf
Author Response
The Authors would like to thank this Reviewer also for reviewing the manuscript. We greatly appreciate the Reviewer for the comments and suggestions. Please find attached a point-by-point response to all comments. All changes were marked in colour in the manuscript. We hope that our responses will be satisfactory.
Reviewer comment: The paper makes the observation that reliable estimation of low flow hydrology is key to successful water management in Poland and other countries particularly for small, rural water supply systems. The study analyses 12 seasonality indices for the regionalization of low-flow characteristics in the Upper Vistula River Basin in Poland. The paper should be of interest to readers of the journal since, as the authors state, many communities rely on diversions from watercourses in natural catchments.
The paper is largely well written with some significant grammatical errors in the introductory sections. These issues can be largely addressed with improvements in grammar and improved explanation of concepts. There is a certain amount of repetition in the introductory section which should be streamlined.
Authors’ answer: We sincerely thank Reviewer for the nice and complimentary words about our manuscript. We agree with Reviewer about there were some grammatical errors and repetition in the introductory section.
Reviewer comment: The review of literature cites an adequate number of relevant papers however very few of the papers cited are current - the majority are papers from the 1970's and 1980's. The majority are references to Polish publications. I would like to see more recent publications cited and a broader inclusion of papers on relevant topics from other countries.
Authors’ answer: Thank the Reviewer for comments In accordance with the Reviewer's suggestion, we expanded the introduction by adding relevant inclusions, supported by 8 recent literature references (no Polish items were added). In addition, to change the proportion of references to Polish literature we removed some Polish references, including those from the 80's. One Polish item from 1977 was left in the introduction, as it is one of the first analysis of seasonality.
Brunner, M. I.; Tallaksen, L. M. Proneness of European catchments to multiyear streamflow droughts. Water Resources Research, 2019, 55, 8881–8894. DOI: https://doi.org/10.1029/2019WR025903.
Floriancic, M. G.; Berghuijs, W. R.; Molnar, P.; Kirchner, J. W. Seasonality and drivers of low flows across Europe and the United States. Water Resources Research, 2021, 57, e2019WR026928. DOI: https://doi. org/10.1029/2019WR026928.Również, zgodnie z sugestią
Dierauer, J. R.; Whitfield, P. H.; Allen, D. M. Climate controls on runoff and low flows in mountain catchments of western North America. Water Resources Research, 2018, 54(10), 7495–7510. DOI: https://doi.org/10.1029/2018WR023087
Serrano, L.; Ribeiro, R.B.; Borges, A.C.; Pruski, F.F. Low-Flow Seasonality and Effects on Water Availability throughout the River Network. Water Resour. Manag. 2020, 34, 1289–1304. DOI: https://doi.org/10.1007/s11269-020-02499-3.
Vlach, V.; Ledvinka, O.; Matouskova, M. Changing Low Flow and Streamflow Drought Seasonality in Central European Headwaters Water, 2020, 12, 3575. DOI: https://doi.org/10.3390/w12123575.
Laaha, G. A mixed distribution approach for low-flow frequency analysis –Part 1: concept, performance and effect of seasonality. Hydrology and Earth System Science, Discussions, 2022, DOI: https://doi.org/10.5194/hess-2022-195.
Pournasiri, P. M.; Pal, I.; Lall, U.; Naveau, P.;Towler, E. Variability patterns of the annual frequency and timing of low streamflow days across the United States and their linkage to regional and large-scale climate. Hydrological Processes, 2019, 33(11). DOI: 1569–1578. https://doi.org/10.1002/hyp.13422.
Fangmann, A.; Haberlandt, U. Statistical approaches for identification of low-flow drivers: Temporal aspects. Hydrology and Earth System Sciences, 2019, 23(1), 447–463. DOI: https://doi.org/10.5194/hess-23-447-2019.
Reviewer comment: The authors use the term uncontrolled catchments throughout. the flow may be uncontrolled draining from a catchment but there is no such thing as an uncontrolled catchment. These and similar grammatical errors have been highlighted in the attached review copy of the manuscript and need to be addressed.
Authors’ answer: Thank the Reviewer for comments. We very much appreciate the errors highlighted and have corrected them. We agreed with the Reviewer that “catchments aren't controlled. Flow can be controlled.” And we change in the paper “uncontrolled catchments” to “ungauged catchments”.
Odnieśliśmy się także do zaznaczonych w tekście komentarzy:
We slight changed the sentence: “Low-flow characteristics are also needed in water management, for licensing of water exploitation, discharges of treated wastewater and the associated location of wastewater treatment plants [1,2,3].”
on: “Low-flow characteristics are also needed in water management, for water intake permits, discharges of treated wastewater and the associated location of wastewater treatment plants [1,2,3].”
We changed the sentence: “River low flow is also the last phase of reaction to water supply deficit [4,5,6].”
on: “Increased demand for water during periods of low flows may increase water deficits.”
We slight changed the sentence: “In addition, the Water Framework Directive requires the estimation of low flows to assess the status of water bodies [2].”
on: “In addition, the application of the Water Framework Directive requires the estimation of low flows to assess good state of water bodies [2].”
We changed the sentence: “This is an issue of particular relevance to water management and especially for small water supply systems for which there is a need to develop a design concept for water demand. The water intakes for such systems usually take water from watercourses located in uncontrolled catchments. For these objects, data required for designing new intakes are missing.”
On: “This is an issue of particular relevance to water management and especially for small water supply systems for which there is a need to develop a project for water intake. The water intakes for such systems usually take water from watercourses located in ungauged catchments.”
We changed the sentence: “This is important in relation to the assessment and monitoring of the hydrological regime of rivers, as well as the impact of climate change on low flows in relation to rational water management [12,13]. Analysis of the seasonality of the occurrence of low flows can also be used to regionalise them, but analyses concerning this issue are rarely performed [2].”
On: “This is important in relation to the assessment and monitoring of the hydrological regime of rivers, as well as the impact of climate change on low flows [14,15].”
We slight changed the sentence: “The analysis was determined for 10 regions and for the entire study area.”
On: “The analysis was performed for 10 regions and for the entire study area.”
We changed the sentence: “Estimation of any low-flow characteristics is not a problem, in the case of a controlled catchment. Then, direct statistical methods can be used to determine them [23].”
On: “Estimation of low-flow characteristics in the case of a gauged catchment is made with use direct statistical methods.”
In accordance with the reviewer's suggestion, we have corrected the purpose of the work to: “The aim of the study is to determine the values of seasonality indices for the regionalization of low-flow characteristics in the Upper Vistula river basin. As a predictive model a stepwise multiple regressions based on physical catchment characteristics and seasonality indices was used. The results of the studies can be used to estimate q95 flows in ungauged catchments and also in practice for modernization and design of new water intakes for small local water supply systems.”
Reviewer comment: The modeling section is weak and requires better explanation and improved discussion of certain parameters. It isn't clear to the reader what months comprise a winter versus a summer flow regime - these need to be better defined. Since this section is critical to the sections that follow the authors need to pay special attention to attending to this section of the paper.
Authors’ answer: Thank the Reviewer for comments. We agree with the comments. We add necessary explanation to the comments highlighted in the text.
Lines 144-145: How are the summer and winter periods defined. What are the dates for each?
We add an explanation: “Seasonality Ratio (SR) representing the ratio of summer (q95s) to winter low flow characteristics (q95w) – Eq. 1. At first daily discharge data have been divided into summer discharge series – from 1 May to 31 October – and winter discharge series – from 1 November to 30 April in order to differentiate summer low flows caused by precipitation deficit and winter low-flow events caused by snow accumulation and frost in highland and mountain areas [17]. Then, from summer and winter discharge time series data, characteristic values of q95s and q95w were calculated for each catchment.”
Lines 155-157: What does this mean? Days? How is this determined?
We add an explanation: “The index is based on two parameters, Θ and r, which are calculated from the Julian dates of all days of the observation period when discharges are equal or lower to Q95. The parameter Θ represents a measure of the average seasonality of low flows by the average day of low-flow occurrence in radians. The value of the parameter ranges from 0 to 2π, where: Θ = 0 relates to 1 January, relates to 1 April, π relates to 1 July and relates to 1 October. For each catchments, the days when the flow was less than Q95 were taken for further analysis and then were transformed into Julian dates Dj.[17, 26].”
Line 136: What are x and y? How determined?
We add an explanation: “xθ and yθ are the arithmetic mean of Cartesian coordinate of a total of n single days j and are calculated as – Eq. 4”
Lines 173-174: How are these factors?
We add an explanation: “In the case of this parameter the shape of the distribution depends on all days when the discharge of a catchment falls below the threshold Q95”
Line 194: Explain the importance of these tests for the interested reader.
We add an explanation: “It is important to check multicollinearity to see if the independent variable is highly correlated with one or more of the other independent variables in the multiple regression equation. The presence of multicollinearity makes statistical inference less reliable. Another parameter, homoscedasticity identifies dissimilarities in a population. Any variance in a population or sample that is not even will produce results that are skewed or biased, making the analysis incorrect or worthless. Checking the normality of residuals is crucial and is one of the main assumptions of a linear regression model. If the residuals are not normally distributed, then model inference (i.e., model predictions and confidence intervals) might be invalid.”
Line 220: we change “the observe value” on: “the observed value”
Lines 228-230; 263-266: What are the impications of this finding? Why is this important?
Since the same remark applies to the SR indicator (page 7) and SI (page, 8) and in order not to repeat the same information we have included an explanation on page 8 and we added: “Knowledge of the low flow seasonality is an important aspect during the planning, as well as the operation of surface water intakes. The results show both spatial and temporal variability of low flow, which is important for administrative decisions on the development and management strategy of an area. Water availability, represented by low flows, is used to define the water permit limit for water withdrawal as a tool for water management and planning [13].”
We changed the sentence: “However, a more detailed histogram analysis allowed to distinguish catchments of mixed type (9 catchments).”
On: “However, a more detailed histogram analysis made it possible to identify catchments of mixed type (9 catchments).”
Reviewer comment: The conclusions section is good but could do more to speculate on the potential applications of the study and in particular how this data may be used. The authors cite applications without any details of how the information might be used to inform decision making. this would be a useful addition.
Authors’ answer: Thank the Reviewer for comments. We add some explanations:
“Information on streamflow patterns throughout the river network is needed to provide useful information to all concerned, which can then be used to propose regulations that are consistent with the hydrological patterns of each catchment. Analysis of the seasonality of low flows can provide water management information by revealing when low flows are likely to occur and by providing context for predicting the regionally varying impacts of climate change on low flows.”
