Event-Based Rainfall Interception Modeling in a Cerrado Riparian Forest—Central Brazil: An Alternative Approach to the IS Method for Parameterization of the Gash Model

Round 1

Reviewer 1 Report

I have attached a marked up copy of the manuscript PDF. I found just a few edits for the authors to include.

Comments for author File: Comments.pdf

Author Response

We would like to thank the reviewer for his dedication to improving the work. We promote all suggested changes as follows:

Line 45-47 – The sentence was changed to a clearer form:

Gash considered that the meteorological conditions prevailing during any wetting-up of the canopy are sufficiently similar to those prevailing for the rest of the storms - so the Gash model considers that evaporation/precipitation rate is constant during the rainfall event.

Line 51 – grammar correction was made: author - authors

Line 79 – grammar correction was made: trees – tree

Line 93 – grammar correction was made: little – small

Line 140 – vocabulary change: derivate – derive

Line 163 – Figure 4 legend was changed to better explain the images.

Figure 4 - Hemispheric image from the plot area. The left image displays the geometric adjustment grid for lens distortions. The image on the right shows the product of high contrast processing for classification of areas with leaf coverage (black) and sky (white).

Line 291 – grammar correction was made: As pointed before - As pointed out before.

Reviewer 2 Report

Comments on "Event-Based Rainfall Interception Modeling in a Cerrado Riparian Forest - Central Brazil: an alternative approach to the IS method for parameterization of the Gash model" by Bruno Távora and Sergio Koide submitted to Water.

When I reviewed this paper at first time, I pointed out the major issues for its publication on any scientific journals. I regret to say, however, that any substantial corrections have not been done based on my previous suggestions, and therefore I recommend to reject this article for publication.

Again, I suggest the major issues for this paper.

When establishing the model to simulate interception loss, scientists MUST use valid and precise measurement data. If data includes uncertainties, model also MUST have fatal errors. The current data of throughfall had 20% error of throughfall. This is clearly not suitable for scientific analysis. I completely cannot understand why a 20% error of throughfall is okay for this paper. I have NEVER known that published papers used the data with the error of more than 10% of throughfall.

Also, I CANNOT agree with the ignoring stemflow. Why authors can conclude that stemflow is negligibly small? Authors used reference no.9 to explain this, but it is not written in English, so I cannot understand the reason. Manfroi et al (2004) and González-Martínez et al (2017) clearly showed that significant contributions of smaller trees to total stemflow amount of forests. Figure2 of this paper shows that this cite includes relatively larger number of smaller trees. Now scientists have known the importance of stemflow generated from smaller trees based on Manfroi et al. (2004) and González-Martínez et al (2017). If authors declare that Cerrado riparian forests are not studied well, careful measurement and analysis of stemflow is necessary to evaluate the interception process and to establish interception model.

Readers cannot understand what degree of improvement is obtained by using PSO. Showing simulated throughfall results with/without PSO is quite required, after the overcoming the issues of throughfall error.

This paper ignored the stemflow, and overestimated the amount of interception loss. Thus, larger E/R and S should be obtained from the overestimated dataset. Quantitative and precise data MUST be needed to do any simulation approach.

Author Response

We understand the concern raised by the reviewer 2. The uncertainty in the measures is high. It turns out that, as we explained earlier, the spatial variability of the throughfall phenomenon is responsible for this uncertainty. That is, it is something inherent to the observed phenomenon. Unlike the article that we are in the submission process, the vast majority of articles simply do not discuss the question of measurement uncertainty in depth. However, those works have their merit and are still published. An example of this is an excellent study by Liu and Zhao (Water, 2020) - https://doi.org/10.3390/w12061731. In this study, the authors used the observed average of five rain gauges positioned below the canopy to measure throughfall. The authors did not address and did not bring the measurement of uncertainty. Another example is the article by Zabret and Sraj (Water, 2020) -https: //doi.org/10.3390/w11122659 where the authors promoted measurement of throughfall with different samplers but, again, did not present the results of uncertainty in the measurements. Some studies are dedicated exclusively to understanding the variability of this phenomenon, such as https://doi.org/10.1007/s11629-019-5424-9 Zhang et all. (J. Mt. Sci., 2019).

On the issue of stemflow, the reverence brought in the article and which supported our option for not spending effort in measuring this process, unfortunately, is found only in the Portuguese language. However, it was published in the best hydrology journal in the country, under the guidance of an important Japanese researcher naturalized here in Brazil.

Reviewer 3 Report

Dear authors,

I consider that the paper is very interesting; however, several issues make it not suitable to be published under these conditions. I consider that you should discuss the term splash in the intro because it is another part of the rainfall. Also, the composition of the rainfall affects the final results. I miss a discussion or mention of the different devices to be used during the interception/drop fall measurements. I include traditional references of these terms, but you can avoid them and select other, if you find better ones. At least, mention why this. The figures must be improved using colours and higher resolution, not it seems old-fashioned ones. The discussion and conclusions must be split up and the discussion much longer including comparisons to other models, advantages, devices, etc. See attached more comments.

Comments for author File: Comments.pdf

Author Response

Reviewer 3 –

We would like to thank the reviewer for his dedication to improving the work. We believe that the contributions of reviewer 3 were important for the refinement of both the introduction and the discussion of the work. The suggestion of reading about the splash opened our eyes to the contribution of this process to the interception of the canopy (which was new to me) and to the already known soil erosion. We also promoted a discussion on some types of collectors, using the suggested references. The different types of collectors seek to overcome the question of uncertainty associated with the spatial variability of the throughfall phenomenon. We have not advanced in the application of other models such as the Rutter model due to the lack of climatological data in the experimental areas. It was in this sense that the Gash model proved to be adequate.

We promote all suggested changes suggested at PDF file as follows:

We add a probable implication to the abstract.

We provided missing references.

We add references to different throughfall collector devices.

We also modify figures adding colors and improving resolution (We also must comment that figures are sent in the separated file (JPG) with full size as demanded during the submission process).

Round 2

Reviewer 3 Report

Dear authors, congratulations on this improvement of the paper. I do not have more to say about this ms. The authors improved the intro, discussion and figures.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments on "Event-Based Rainfall Interception Study in an Undisturbed Riparian Forest in Central Brazil" by Bruno Távora and Sergio Koide submitted to Water.

This paper measured gross rainfall, throughfall and canopy openness, and estimated the interception loss and the free throughfall coefficient. Also, it applied Gash type interception model. Authors suggested that the forests in Cerrado have not been studied well, especially for the interception process. I could understand the importance of the study investigating interception process in Cerrado, but I cannot understand what this paper want to do. Authors want to make clear the process of interception and to quantify the amount of interception loss? Or, they want to establish simple model to estimate interception loss? Please referring to the following comments very carefully, and do the major and substantial revisions before the publication on any scientific journals.

General comments

At first, authors must determine the main purpose of this paper. It should be "first and precise estimate of interception loss of the forest in Cerrado". The current introduction is too general and too long. To achieve this, careful and high quality measurements of gross rainfall, throughfall and stemflow must be required. If authors do not know the actual values of rainfall, throufhfall and stemflow, any developments of models cannot be done.

To obtain the precise throughfall data, the current methodology is safely enough? Authors applied 11 rain gauges to collect throughfall, but the estimation error was 20% for larger rainfall event, or more than 20% for smaller rainfall event (line 216). This error is critically large. The interception ratio of 24.7% for annual value is larger than the annual scale error?

  Recently, dynamic calibration to correct systematic underestimation of rainfall intensity by tipping bucket rain gauges had been applied, and -20 to +40% changes in interception was reported for event scale (Iida et al., 2012 Hydrological Processes; Iida et al., 2018 Journal of Hydrometeorology). Authors used 5 minutes intervals, so the underestimation must be larger than event scale. Authors should apply the dynamic calibration to their data to obtain more reliable measurements.

  I cannot know the forest situation despite reading the manuscript. How many trees are there in your measurement plot? Why can you ignore the stemflow? I could predict that there are big trees in your plot, reading the description in line 110-111, tree height from 4 to 21.5 m, DBH range from 9 to 67 cm. Also looking at Figures 2 and 4, your site includes not only main canopy trees but also understory vegetation and lower canopy trees. Under like this condition, stemflow cannot be ignored to derive the first and precise estimation of interception loss. Authors must measure the stemflow, if they would not have the quantitative evidence showing smaller contributions of stemflow to interception process in this site. Please note that smaller trees also contribute largely to stemflow amount (Manfroi et al., 2004 Hydrological Processes).

Specific comments

Line 17

Readers cannot understand what PSO is, here.

Line 22-23

Can you safely conclude this with ignoring stemflow?

Line 27-96

The current introduction is too long. Should be more concise. Especially, line 70-76 should be removed.

Line 92

"Gashinterception" should be "Gash interception".

Line 112-115

How many trees in your plot? 100 m2 plot is enough large to represent the biome? 10 m x 10 m grid is true? It is 1 m x 1 m grid?

Line 156

"steamflow" should be "stemflow". Why authors can ignore stemflow?

Line 183

Typo "mfive".

Line 213-216

Readers want to know the error for 35 events, and its total amount. Error ratio is smaller than interception ratio?

Line 228-235

Why authors can say this? The contribution of stemflow is evaluated?

Line 253

"poor sampling of the free throughfall" could be resulted from the relatively limited number of rainfall gauge (11 gauges)? Eleven gauges are safely enough to do this analysis?

Line 236-320

Authors described the results of comparison in model parameters here, however, I cannot understand what authors want to say. The validity of the model and parameters must be checked by measured data and calculated one.

Moreover, more important thing is that, in this plot, there is no previous measured data, even in the Cerrado. The precise and reliable measurements of rainfall, throughfall and stemflow must be required to establish the suitable model which simulates interception process in this biome. I highly and absolutely recommend that authors should measure the gross rainfall, throughfall and stemflow with the suitable methods considering sampling number of point throughfall and stemflow, and dynamic calibration for rain gauges to measure rainfall/throughfall/stenflow. Finally, they will evaluate the accurate amount of interception loss, and will apply the model to simulate interception process in this biome.

Line 328-330

This is valid without considering the stemflow contributions?

Line 335-337

The difference between "0.03 to 0.13" and "0.17" is significant?

Line 339-340

Also, this is valid without considering the stemflow contributions?

Reviewer 2 Report

See attached document

Comments for author File: Comments.pdf