the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
On the regional-scale streamflow variability using flow duration curve
Jeenu Mathai
Murugesu Sivapalan
Pradeep Mujumdar
Abstract. As each catchment responds uniquely, even if they appear similar, formulating generalizable hypotheses and using routinely used signatures of catchment similarity to examine streamflow variability can be difficult. Flow Duration Curve (FDC), a concise portrayal of streamflow variability at a specific gauging station, can provide insights into hydroclimatic and landscape processes occurring at a wide range of space and time scales that govern flow regimes in a region. This study explores the suitability of partitioning of annual streamflow FDC into seasonal FDCs, and total streamflow FDC into fast and slow flow FDCs to unravel the process controls on FDCs at a regional scale, with application to low-gradient rivers flowing east from the Western Ghats of Peninsular India. The focus is on investigation of the controls of common regional landscape features (in space) and seasonal climatic (in time) variations on regional variations of the FDC. Findings of the study indicate that bimodal rainfall seasonality and higher fraction of moderate to good groundwater potential zones explains the higher contribution of slow flow to total flow across north-south gradient of the region. Shapes of fast and slow FDCs are controlled by recession parameters revealing the role of climate seasonality and geologic profiles, respectively. A systematic spatial variation across north-south gradient is observed– highlighting the importance of coherent functioning of landscape-hydroclimate settings in imparting distinct signature of streamflow variability. The framework is useful to discover the role of time and process controls on streamflow variability in a region with seasonal hydroclimatology and hydro-geologic gradients.
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Pankaj Dey et al.
Status: final response (author comments only)
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RC1: 'Comment on hess-2023-178', Anonymous Referee #1, 30 Aug 2023
The paper by Dey and coauthors “On the regional-scale streamflow variability using flow duration curve” explores the spatial patterns of flow duration curves across the Peninsular India, with the aim of identifying the main drivers of the water resources in a complex lowland region dominated by Monsoons. The analysis is performed by applying a “sepration method” to disentangle fast and slow runoff components, and a “decomposition method” to express the annual FDC as a function of the underlying seasonal FDCs. The main results, as stated in the abstract and in the conclusions, pertain to the identitification of the role of recession parameters and rainfall regime in the observed patterns of flow duration curves across the focus region.
While the study of FDCs in the Peninsular India is potentially interesting, the paper is very long (approximately 40 pages and 14 figures) and not always easy to read.
I must note that the quality of the Figures is not sufficient in most cases: some Figures contain contain a lot of panels with super-small labels and axis titles, which are nearly impossible to read and understand (e.g. Figure 2, 4, 5, 8 and 14).
From the perspective of the presentation, I think it would be necessary to implement the following key actions to improve the quality of this work and make it publishable:
- Condense the Ms text, focussing on the few real novel elements of this analysis
- Improve the quality of the presentation, including clarity, typos, Figures quality, references – see below
The title of the paper is quite vague, and does not tell nothing about the specific contribution of this paper. “Regional streamflow variability in Peninsular India” or “regional-scale variability of flow duration curves in Peninsular India” seem to be better options.
In spite of the length of the Ms., the methods used are not new. The decomposition of timescales (Seasonal vs annual FDCs) – which is somewhat trivial from a statistical perspective - has been already applied in several past studies (e.g. Botter et al., WRR 2008; Muller et al., WRR 2014, Durighetto et al., WRR 2022). My impression is that this is not recognized in the text, and the approach is – implicitely - declared as a new contribution of the work (given the emphasis the authors put on this issue at the beginning of the methods).
Likewise, the decomposition of FDC into fast and slow components is the one proposed by Ghotbi et al., 2020 and 2021 (which in turn relates to concepts already well known in the literature, see e.g. Stewart, HESS 2015 and Leong and Yokoo, HYP 2022). Incidentally, this approach has its own limitations, provided that it is based on an empirical (subjective) filter to decompose the total streamflow into a fast and a slow component.
Thus, this paper represnts a regional scale application of existing methods, with the reasonable aim of analyzing the spatial patterns of FDC in the Peninsular India. In the light of the scope of HESS (substantial new concepts, ideas, methods), Journal of Hydrology: regional study seems to be a better fit for this paper.
In terms of methods (and presentation of the methods), I have the following additional major concerns:
- The first 16 equations of the paper are really trivial, and defintiely not new. This needs to be recognized in the paper (and this part of the paper needs to be shortened);
- I really miss the very reason for which the decomposition of timescales is presented in the main text, while the decomposition into fast and slow runoff components is reported in the appendix. Both these methods are not new, and this paper presents an application of existing techniques. Both the key methods used in the Ms. (timescales separation and flow component separation) need to be summarized in the main body, although properly acknoledging previous works where these methods have been proposed /used.
- The recession analysis used in this paper is very basic, and most of the literature on the topic (which is huge) is overlooked. Recession analysis is a very delicate and tricky issue and has limits, artifacts and caveats that need to be recognized. The authors, therefore, need to better put this work in the context of the existing literature on recession analysis, including the following papers: Stewaert, HESS 2015; Jachens at al., HESS 2020; Biswal and Marani, GRL 2011; Rupp and Selker, AWR 2006; Dralle et al., GRL 2015, Basso et al., AWR 2015)
- The use a gamma FDC is not new, as it was intrduced and used by many others, e.g. Krasovskaia et al., CVC 2006; Botter et al., WRR 2007; Muller and Thompson HESS 2016, Santos et al., HESS 2018
More in general, the problem of identifying the main drivers of flow duration curves is quite old in hydrology, and I would say it has been already resolved/ discussed in several previous studies, including (but not limited to) Leong et al., HYP 2022; Carlier et al., JoH 2018; Botter et al., PNAS 2013; Basso et al., AWR 2015; Ye et al., HESS 2012; Fenicia et al., HYP 2014. This paper should summarize what is already known from the literature and indicate to what extent this paper advances the state of the art, providing a stronger link with other theoretical, modeling and regional scale studies.
In line with the above comments, in terms of results / conclusions, the paper provides several arguments that are well known or somewhat tautological. For instance, the core part of the abstract states that: “Findings of the study indicate that [...] higher fraction of moderate to good groundwater potential zones explains the higher contribution of slow flow to total flow across north-south gradient of the region. Shapes of fast and slow FDCs are controlled by recession parameters.”
I think everyone can agree on the above statements. The idea that good grondwater potential enhances slow flows is not particularly groundbreaking, and should not be reported in the abstract.
Likewise, the key role of recession parameters in the definition of the shape of the flow duration curve has been discussed by several previous studies (Mandal and Cunanne, INHS 2009; Botter et al., PNAS 2013; Muller et al., WRR 2014; Basso et al., AWR 2015; Arai et al., JoH 2021; Leong and Yokoo, HYP 2022; Leong and Yokoo, HRL 2019) which are not properly acknowledged here.
Were this work better placed in the context of the existing literature, and the presentation improved as per the above recommendations, the reader could better value the novel contribution of this paper, and the insight deriving from the regional-scale application presented in this HESSD manuscript. This would require extensive revisions and a deep restructuring of the Ms., but would ultimately lead to a shorter, more comprehensive and stronger work, in which the specific insight provided by the authors and the links /connections with the existing literature are better articulated.
In case the authors need more info on the references included in this review in a condensed format, they are encouraged to contact me through the Editors, and I will be happy to provide the full list in a standard format.
Citation: https://doi.org/10.5194/hess-2023-178-RC1 -
RC2: 'Comment on hess-2023-178', Chris Leong, 03 Sep 2023
This paper tests FDC partitioning into fast and slow flow FDCs to identify the process controls on catchments in the Indian peninsular.
Although it seems to claim to be a novel approach, the framework is not new. Perhaps the approach is new to the region, therefore, although I would recommend publication after attending to my suggestions below, I strongly suggest this paper be transferred to a regional journal.
My comments are listed below.
Title- Title is too general, needs improvement.
Introduction
Line 56-72. It is good that the authors have cited the keystone FDC paper (Yokoo and Sivapalan, 2011) that disaggregates the FDC. However, there is repeated referencing in the paragraph which contributes to the long length of this paper. I suggest dedicating the paragraph to summarizing the keystone paper- so that it reduces citation repetition.
Lines 60-62. “Therefore, there is a need for appropriate conceptual frameworks that can bring out these process controls of FDCs and generate deep insights into the governing principles underpinning observed variability.”
This may need rephrasing, as I think it works the other way around---i.e., identify the process controls to deliver appropriate conceptual frameworks and generate deep insights into the governing principles underpinning the catchments variability.
Lines 92-97 “The scientific novelty and methodological advancement of the paper lie in two interconnected aspects, which have not been adopted in the literature to date: (i) the timescale partitioning framework is used to study the relative contributions of different seasons to the FDC (repeated for fast and slow flow components), exploring how the relative contributions holistically vary across the whole region and using the framework to reconstruct the annual flow duration curve using seasonal flow duration curves, (ii) the Wegenerian approach in connecting the spatial variability of streamflow at a regional scale using flow duration curve”
In my opinion it is certainly not novel/new as similar studies have already been conducted especially (Chouaib et al., 2018, 2019 (https://doi.org/10.1016/j.jhydrol.2018.01.037, https://doi.org/10.1080/02626667.2019.1657233). To compare to other similar studies, and identify what makes theirs novel or different from the others, the authors may want to look at Leong and Yokoo 2021 (https://doi.org/10.1016/j.jhydrol.2021.126984) that reviews the FDC from 2000-2020, as it is during this time that flow/time partitioning begun to generate more interest and development.
Nevertheless, I still think the only difference is the approach is novel (or advancement) to the study region (comparing to other FDC studies conducted in and around the surrounding Himalayan region—could identify the novelty of the work in the area), but the idea and results are certainly not new. Therefore, I might suggest stating the novelty as such in addition to considering publishing as a regional paper. FDC literature is flooded with regionalization studies of similar nature, and the authors should not find difficulty identifying the strong points of their paper.
Lines 82-106 is a long read; I suggest to split the paragraphs.
Line 92-93. “The scientific novelty and methodological advancement of the paper lie in two interconnected aspects, which have not been adopted in the literature to date”:
I disagree, it already has been adopted and applied in different regions. Rephrase??
Line 97-99. So, is the paper an extension of Ghobi et al, 2020a with time partitioning? If so, I don’t see a problem statement in the MS, what is lacking in the Ghotbi paper that the authors are trying to address, did the study lack time inclusion? If not, then remove the citation for this part as it is unnecessary and confusing.
Method
Line 121-145 is long and needs splitting
Figure 1. Improve the visibility of the figure (i.e., font size of the legend and coordinates), and general map indicators (e.g., scale and direction). After going through all the figures, generally, improve the visibility of all figures. Also, is it appropriate to label (i.e., a, b, c, etc.) within the boundary of some of the figures---move them top-left of each sub-figure?. There are too many figures in the MS- 14 figures, consider moving some to supplementary (e.g., Figure 6)
Could section 2.” Study region”-- be summarized and move some parts to supplementary material, as the main part of the method begins in Section 3. Otherwise, it just contributes to the long length of the paper.
In Section 3. The governing equations are not cited.
Maybe I missed it but what are the demarcations of fast and slow flows or how did the authors decide what was fast and slow? This needs to mentioned because of the recession parameter analysis in Figure 12.
Results
In the results section of the paper, I must argue-- are again not new, I struggle to find what stands out from the results, if the authors can clearly state some new findings would certainly strengthen the novelty claims. Perhaps figures 9 and 13 (and Lines 603-603) are proof that this paper should be published in a regional journal
The results section could be titled “results and discussions”??
Conclusion
Lines 600-602- “Motivated by this fact, in this study we outlined a framework and its suitability for understanding process controls of FDCs, which involved separating annual streamflow into seasonal flow components and constructing annual FDC using seasonal FDCs.”
I could not clearly identify what was the framework was. It seems that the framework the authors are using has already been developed and just testing the efficacy in a different region (see Lines 602-603). I’m confused as to whether the paper uses an existing framework. or develops a new framework (if so, —could a paragraph in the results section explain/describe the new framework).
The conclusion needs to be summarized ---it is repetitive of the results section--just choose few outstanding points that need to be highlighted. And move some parts to introduction (e.g., Lines 664-678).
Citation: https://doi.org/10.5194/hess-2023-178-RC2 -
RC3: 'Comment on hess-2023-178', Anonymous Referee #3, 07 Sep 2023
General:
Flow duration curves (FDCs) are used widely in hydrological practice. They provide valuable information that can be used as catchment-specific signatures. The paper takes FDC as the topic to study by using a large set of streamflow data from 62 gauging stations extended over four neighboring large river basins in southern half of India. The streamflow data set extending from 1965 to 2012 at daily time interval is accompanied with daily gridded rainfall data at fine spatial resolution. Conceptualization of the methodology is based on the similarity of FDC as a hydrological tool, and Cumulative Probability Distribution Function (CDF) as a statistical tool. The streamflow was divided into three timewise partitions (non-monsoon, SW monsoon and NE monsoon) and into two processwise partitions (fast flow and slow flow) to determine relative contribution of each season and process to the annual flow. Results show how the contribution of each timewise and processwise partitions varies over the river basins selected in the study. Based a multiple regression analysis, this variability was connected to the climatic and physical characteristics of river basin, and also to the parameter sets of probability distribution functions fitted to the streamflow data. Summarized as above the study is worth to review.
Specific:
- Introduction is a relatively concise and well written section with relevant literature summary. However, the novel (better we say the new) part of the study was not clearly expressed (Lines 86 onward where “the extension of the method” is mentioned + Line 97-99 where the main goal of the study is given and the extension of the process partitioning (Ghotbi et al., 2020a) with the time partitioning was mentioned). A clearer way of presentation of the new/novel piece is required to avoid any misinterpretation about that the paper is a repetition of earlier studies.
- Equations (1) and (2) are linked to each other as given in the paper correctly. One detail is that: The cumulative probability in Equation (1) is the probability that the variable (Q) is less or equal to a given value of variable (q). The probability we get from FDC is the probability that the variable (Q) equals or exceeds a given value of variable (q). Then, to satisfy the most right side of Equation (2), the middle part of Equation must be P[Q>q] not P[Q>=q]. Then, this will not be in accordance with the definition of FDC. I am commenting about this not to say that Equations (1) and (2) are incorrect but to remind this detail which is practically nill as we know that, for a continuous variable such as streamflow here, probability that the variable gets a given value is zero because of the infinite number of possible outcomes. It might be good to put this detail in a sentence after Equation (2).
- Reading the paper by shifting among the main text, appendix and supplement is not easy. My suggestion would be to put some pieces from the supplement to either directly into the text or give in the appendix by at the same removing well-known parts. Two examples; I would suggest moving Figure Figure S3 into the main text to come in Line 276, which is needed to explain the estimation method. Also, I would suggest removing the well-known details of the baseflow separation and multiple regression in the Appendix (A1, A5). This comment is applied to the rest of Appendix and Supplementary.
- Section 4 needs a revision to better explain the use of methodology. In its current version, the section is not understandable probably becuse of shifting from time-scale partitioning to other types of partitioning, and also because of skipping from the main text to the Appendix and to the Supplement.
- While revising the paper, the authors may give less emphasis to the study area but more to express the generalization of the methodology, otherwise the paper will seem like a regional study.
- Figures’ readability is low because of too many figures in one and also small size of fonts. An improvement is needed for the readability.
Corrections:
Line 165: Mistyped catchment area 2,60,000 km2
Line 169: Correct ‘bout’ as ‘about’
Line 263: ‘where, 𝑚 = 1, 2, . . . , 12, represents the index for months’ not needed, m already defined in Line 257.
Line 284: DELETE ‘the’
Line 293: to plot of the flows ?
Line 520: Change ‘&’ with ‘and’
Line 671: (cf. Alfred Wgener, Sivapalan, 2018): not listed or not properly listed among the references.
Citation: https://doi.org/10.5194/hess-2023-178-RC3
Pankaj Dey et al.
Data sets
IMD New High Spatial Resolution (0.25X0.25 degree) Long Period (1901-2022) Daily Gridded Rainfall Data Set Over India. D. S. Pai, Latha Sridhar, M. Rajeevan, O. P. Sreejith, N. S. Satbhai, and B. Mukhopadhyay https://www.imdpune.gov.in/cmpg/Griddata/Rainfall_25_Bin.html
India Water Resources Information System for observed streamflow datasets Central Water Commision, Ministry of Water Resources, Government of India https://indiawris.gov.in/wris/#/
Pankaj Dey et al.
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