Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions

Anderson, R. G.; Wang, D.; Tirado-Corbalá, R.; Zhang, H.; Ayars, J. E.

doi:https://doi.org/10.5194/hess-19-583-2015

Articles | Volume 19, issue 1

https://doi.org/10.5194/hess-19-583-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-19-583-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 19, issue 1

Research article

|

29 Jan 2015

Research article |

| 29 Jan 2015

Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions

R. G. Anderson, D. Wang, R. Tirado-Corbalá, H. Zhang, and J. E. Ayars

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Final revised paper (published on 29 Jan 2015)
Supplement to the final revised paper
Preprint (discussion started on 17 Jun 2014)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC C2544: 'Evapotranspiration of sugarcane in tropical conditions', Anonymous Referee #1, 16 Jul 2014
- AC C2863: 'Response to Anonymous Referee 1', Ray Anderson, 01 Aug 2014
RC C2939: 'Review of Divergence of reference evapotranspiration observations with windy tropical conditions, Anderson et al.', M.J. Waterloo, 05 Aug 2014
- AC C3016: 'Response to review by Dr. M.J. Waterloo', Ray Anderson, 08 Aug 2014

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (31 Aug 2014) by Lixin Wang

AR by Ray Anderson on behalf of the Authors (09 Oct 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Oct 2014) by Lixin Wang

RR by Anonymous Referee #3 (09 Nov 2014)

Suggestions for revision or reasons for rejection

Anderson et al (Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions) reported the divergence between actual and reference ET at the windy tropical irrigation fields in the manuscript. I also have read the resubmitted manuscript and the comments by the first two reviewers, as well as the authors’ replies to each comment. Overall, I think that the paper will be useful contribution and the subject matter should be of interest to the HESS readers. Especially decoupling between VPD and ET measurements (also decoupling between atm forcing and soil moisture by irrigation) indicates that very unique stomatal responses of irrigated sugarcanes in this humid and windy environment. I recommend the minor revision with some suggestions and concerns, which I would leave on the authors’ or the editor’s choice.

First, I start with the points posed by the first reviewer. As the authors pointed out in their reply, underestimation of EC based ET is mostly related to frequent rainfall events, which might not be a big problem in this study. Also, the high energy closure (like 97%) was reported in these sites (especially in Windy site, where huge discrepancies among different ET estimates were reported), so I think that EC based estimates are more close to the truth. I don’t think that it can be a reason to reject the manuscript considering the interesting point of the manuscript and their hard works. EC methods were validated in several irrigated fields as the authors mentioned, so I think that citations would be enough. However, it would have been much easier for the authors to have installed several simple lysimeters in the site (especially Windy site) to get another estimates from mass balances in spite of their spatial heterogeneity. I recommend to include the cumulative irrigation+rainfall plots in Figure 5 in the manuscript, which would show at least that the EC measurements are not out of ranges of the mass balances.

Second, the P-T methods were said to be close the EC-based measurements in the cumulative basis. However, I recognized from Figure 5 that their seasonal patterns of all ET estimates are quite different especially for the Windy site. At the Lee site, EC measurements (Figure 5a) followed the P-T ET patterns (Figure 5d), although the amplitude were damped a little. However, those at the Windy site did not. They did not follow the other microclimate measurements, such as wind velocity and temperature (Figure 4). Rather, they seemed to follow the growth of vegetation (as a form of higher vegetation or LAI values) even during the so-called ‘mid-period’. I am not sure that the authors can say that the P-T method was the more accurate method than others just from the totals because it still did not simulate the seasonal patterns well. I think that there should have been explanations regarding this discrepancy. The Windy site has higher wind velocity throughout the season than the Lee site with the sandier soils (more exfiltration I guess) (Table 1). I think that that that explained not just the higher ET measurements and estimates in total, but also its temporal patterns, which might be affected by vegetation height. It was not clear in the manuscript whether the authors incorporate the growing vegetation height in their ET calculation (especially for P-M ET estimates). Note that vegetation cover (%) is not a good indicator to assess the maturity especially in these high density irrigation fields. They can grow in LAI or height values significantly even after 80% vegetation cover. If the authors have some temporal measurements of LAI values, vegetation heights, or other remote sensing datasets (e.g. MODIS NDVI), that would be helpful to find out why. I think that this can be also a key to explain the difference between the two sites in term of the temporal patterns.

In addition, the damped seasonality in EC-ET compared to P-T ET estimates (Figure 5) has been reported as a form of seasonality of the alpha parameter in P-T equations in grasslands and irrigated fields (e.g. Ryu et al. 2008; Ding et al. 2013), as a form of non-linear response of alpha with vegetation seasonality or canopy conductance values. Please add this point with the citations somewhere in discussion.

Third, although the manuscript is generally well-written and quite easy to follow, but still I think that there are some issues in its organization. I can see some addition new methods kept coming (P13 L27 , P14 L10, P14 L23, P15 L1) in Results and Discussion sections. It might be an authors’ choice in writing style, but there are fairly good reasons why most papers are following a strict rule of its organizations (introduction - methods- results - discussion). Please put some technical details into the SI.

Specific point
1. The terms
The term ‘mid-period’: Is this a generally used term in the irrigated field? I am not sure whether this can deliver some information to the readers. ‘Peak growing season’ or ‘maturity season’ would be better if it is not a general term.
P18 L25: The term ‘effective LAI’. It seems that this term is generally used in the calculation of canopy bulk resistance in agricultural fields. But note that this term originally devised to explain the difference between optical measurements (by LAI-2000 or other optical instruments) and actual LAI values (Chen 1996), usually called as a clumping index. It looks more like sunlit LAI values to me. Now, the authors may realize that I mostly have research experience in forests.

P5 L1: Should be italic
P9 L27: Put comma after ‘Finally’
P10 L30 and afterward: The plus-minus-together sign would be better for standard error values
P16 L28-31: I agree.
P17 L9-15: I agree.
P21 L2: I agree.

About the Figures: It is quite difficult to match between graphs because they are using different x-axes scales; dates and DAP (dates after plantations). In this study, crop seasonality is not matching with that of climate, which make it worse. Please just use date, and DAP can be featured by shaded region. I am not sure that the authors need to show some figures in the end (Figure 9 and 11). It would be enough to put them in the Supplementary Information.

References
Ryu, Y., D. D. Baldocchi, S. Ma, and T. Hehn (2008), Interannual variability of evapotranspiration and energy exchange over an annual grassland in California, J. Geophys. Res., 113, D09104, doi:10.1029/2007JD009263.
Ding, Risheng, et al. "Evapotranspiration measurement and estimation using modified Priestley–Taylor model in an irrigated maize field with mulching."Agricultural and Forest Meteorology 168 (2013): 140-148.
Chen, Jing M. "Optically-based methods for measuring seasonal variation of leaf area index in boreal conifer stands." Agricultural and Forest Meteorology80.2 (1996): 135-163.

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RR by M.J. Waterloo (10 Nov 2014)

ED: Publish subject to minor revisions (Editor review) (11 Nov 2014) by Lixin Wang

AR by Ray Anderson on behalf of the Authors (21 Nov 2014) Author's response Manuscript

ED: Publish as is (25 Nov 2014) by Lixin Wang

AR by Ray Anderson on behalf of the Authors (25 Nov 2014)

Short summary

Evapotranspiration (ET) was measured and compared to reference ET over irrigated sugarcane in Hawaii, USA: reference ET increasingly diverged from measured ET with higher wind conditions; custom bulk canopy resistance improved reference ET observations; the Priestley-Taylor equation performed better than reference ET to estimate actual ET; bulk canopy resistance was over 150 s/m, but there was no evidence of water stress in the field.