Creating long-term gridded fields of reference evapotranspiration in Alpine  terrain based on a recalibrated Hargreaves method

Haslinger, Klaus; Bartsch, Annett

doi:https://doi.org/10.5194/hess-20-1211-2016

Articles | Volume 20, issue 3

https://doi.org/10.5194/hess-20-1211-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-20-1211-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 20, issue 3

Research article

|

21 Mar 2016

Research article |

| 21 Mar 2016

Creating long-term gridded fields of reference evapotranspiration in Alpine terrain based on a recalibrated Hargreaves method

Klaus Haslinger and Annett Bartsch

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Final revised paper (published on 21 Mar 2016)
Preprint (discussion started on 28 May 2015)

Interactive discussion

Status: closed

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

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- Supplement

SC C2156: 'Some comments', Aristotelis Tegos, 20 Jun 2015
- SC C2196: 'Reply to "Some comments" by Aristotelis Tegos', Klaus Haslinger, 23 Jun 2015
RC C2347: 'Comments from Referee (Good study, but "major revision" recommended)', Anonymous Referee #1, 01 Jul 2015
- AC C3350: 'Reply to Referee #1', Klaus Haslinger, 27 Aug 2015
RC C2438: 'Reviewer Report', Anonymous Referee #2, 08 Jul 2015
- AC C3351: 'Reply to Referee #2', Klaus Haslinger, 27 Aug 2015

Peer-review completion

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

ED: Reconsider after major revisions (27 Aug 2015) by Jan Seibert

AR by Klaus Haslinger on behalf of the Authors (08 Oct 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Oct 2015) by Jan Seibert

RR by Anonymous Referee #1 (28 Oct 2015)

Suggestions for revision or reasons for rejection

This revision addresses all my earlier comments well. However, I don’t quite agree with the specific numerical approach taken in the new Figure 13. See below.

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New Figure 13 and accompanying discussion: I think you have the right physical idea, but the math you give isn’t quite right. Since DTR is *less* related to global radiation at high elevations, your reasoning would say that a *lower* value of Cadj should be found by the analysis, not a higher value (right?) Since we think of DTR*Cadj as an approximation of radiation in the HM method. Yet you find a very high value of Cadj at these times and places.

So, instead, I think the key mechanism is that the *absolute values* of DTR are so much lower in winter and/or high elevations, compared to “normal” evaporative environments in which the HM was developed. That is, for any given value of cloudiness (or sunshine hours or similar), DTR is much smaller in winter/high elevation than in normal environments (due to the free tropospheric ventilation / mixing mechanism you describe.) So this small DTR needs to be multiplied by a much higher value of Cadj to compensate for this and achieve the right value of radiation relative to Ra.

One way to see this would be to plot the *regression* coefficient of DTR against global radiation, instead of the correlation coefficient. If my idea above is right, this regression coefficient should be much smaller in high elevations (especially in winter) than in low elevations. Even better would be a zero-intercept (y=mx) regression of sqrt(DTR) against the ratio of global to extraterrestrial radiation, since this is the best mathematical match to the HM. (In the HM, sqrt(DTR) seems to be parameterizing this ratio.)

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RR by Anonymous Referee #3 (21 Dec 2015)

RR by Anonymous Referee #4 (03 Feb 2016)

Suggestions for revision or reasons for rejection

This manuscript introduces a new approach to construct daily 1 km fields of reference evaporation. The Hargreaves method is improved and calibrated over space and time against Penman-Monteith. The methods are applied and analyzed over Austria from 1961 to 2013. While I find the method and description logic and appealing and the contribution thus relevant, I am not fully convinced by its presentation in the manuscript. Regarding this I have two major concerns/suggestions:

1) For the content I would recommend to have a separate part that is reserved for the evaluation of the product. This starts with including existing similar products (for instance the maps mentioned by reviewer #2) in the introduction over methods for comparison of the new products with the old ones and general plausibility (as done with the correlation between diurnal temperature range and global radiation in comparison to the Cadj values already) in the methods to their presentation in the results and discussion. This would lead to a clearer message regarding the novelty and the ability of the introduced method.
2) The structure of the paper was not always clear. Often there is a mix between Methods and Results but also between Discussion and Results (see more detailed comments in the specific comments below). I would hence recommend revising the structure of the document substantially.

Specific comments
P5L28- P6L14 These are Results not Method
P6L24- P7L2 Results not Method
P7L7 - L23 Results not Method
P8L3 from “As was shown…” to P8L23
For all the above indicated lines, I see that these are meant to be preliminary results that lead to the further development of the study. However, it disrupted from reading and I had to check several times which section I was reading actually. I would recommend moving all these to Results. The Method section then could be structured to 1) which parts of the method were needed for the development of the method, 2) the application of the method and then finally 3) the evaluation of the method. 1) specifically, could then be structures like this: this and that was tested to…and then mention that based on these results… further steps were taken
P9L31-P10L10 should be reformulated to stress the benefit more clearly
P10L11 From here it would be great to have this evaluation part including the comparison to existing maps as pointed out by reviewer #2, which could impact the discussion on Cadj, and add credibility as well as general advantage of the method proposed to existing methods
P10L26-27 This sentence is not well connected to this paragraph, it would be linked better in a paragraph dealing with this relationship, the consequent Caj values per day and grip point and a comparison to other products and/or the pronounced events that were anyhow exemplary used in the study
P11L7-16 this is not Discussion but Results
P12L10-16 Results not dicussion

Technical comments
There are many formulations that could be expressed easier and more concise, it would be advisable to have a native English person correct for the language in the manuscript. Some of these formulations I picked up below. Generally, the own results are presented in past tense.
P1L19 in -> over
P1L20 the sole predictor -> the only predictor
P1L22 the statistical -> a statistical
P1L24 Having -> with these
P1L26-29 Reformulate to be clearer
P2L2 by the fluxed -> by fluxes
P2L3 the latter -> evapotranspiration
P2L5 “agriculture” does this imply science or the farmer?
P2L24 “have been developed…data.” -> “as alternatives for regions where the input data is not sufficient to used PM.”
P2L25 add “one of these simpler methods” before “, the methods of Hargreaves…”; move ”in this paper” to the end of the sentence
P2L27 by -> from
P2L27-30 rewrite to make this clear: sth like: “Hence, HM is much broader applicable for many regions, because temperature observations are dense and easily accessible. Nevertheless, like most temperature based methods, HM has been developed for distinct studies and regions representing also distinct climate conditions.”
P2L31 add “temperature-based” before methods
P3L1 to -> in; add “in those” before they
P3L3 add comma after “In this paper” and “is presented” after ET0
P3L5 on -> in?
P3L8 similar results compared to PM -> results comparable to PM
P3L12 and the interpolating -> followed by an interpolation of
P3L13 in this paper -> here
P3L22 to use the better -> at using the best
P3L28 The foundation of the ET0 calculations is -> The ET0 calculations are based on
P3L32 remove “and reaching down to the present day”; remove “the conduction of”
P4L2 for -> to
P4L3 to ensure -> at ensuring
P4L4 whole -> full
P4L6 (DEM). The SRTM DEM was also applied in this study.
P4L9 remove the before HM
P4L11 is -> are; change to “to calibrate the HM to PM on a monthly basis” (PM was already introduced before)
P4L12 among the Austrian domain and also comprise rather -> over Austria and cover
P4L15 covering -> for
P4L20 Remove “As explained above”
P4L22 they -> these methods
P5L25 the original publication of
P6L28 remove underscore
P6L30 remove “time of”, change “rather high” to “the highest”
P9L1 remove “the” before higher; it -> This higher ET0
P9L2 higher -> longer?; termed -> known?
P9L4 Northwest no capital (also for the other cardinal directions in the manuscript); specify the “it” not clear like this
P9L6 remove “the” before ET0
P9L7 again -> also; the higher proportion of -> longer
P9L8 enhances indirectly ET0 -> enhance ET0 indirectly
P9L9 remove exemplary
P9L12 bringing -> which brought
P9L13 This is -> These conditions were
P9L14 nearly -> almost
P9L24 Remove “on the other hand” or replace it with instead after “cool,”
P9L28 “which is“ before equivalent
P9L30 remove “the” before some
P910 is generally above the original -> has generally a higher value than Hargreaves original value; in -> during
P10L29 add “was done” after analysis
P10L31 will be -> is
P10L32 are dropping -> drop
P11L1-4 Change to “Numerous studies investigating the relationship between DTR and radiation (Pan…) showed considerable correlations. For example,”
P11L31 add “the coefficient” before C
P12L24 -25 Split sentence in two
P12L29 may be -> is
P12L30 aims to provide -> provides; tries to combine -> combined
Table 1, caption Figure 1: remove underscores
Caption Figure 2 station-> stations remove for before the spread
Figure 15 add July and January at a more pronounced place of the figure not just in the caption similar to Fig 13

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ED: Reconsider after major revisions (08 Feb 2016) by Jan Seibert

AR by Klaus Haslinger on behalf of the Authors (22 Feb 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Feb 2016) by Jan Seibert

RR by Anonymous Referee #4 (29 Feb 2016)

ED: Publish subject to minor revisions (Editor review) (01 Mar 2016) by Jan Seibert

AR by Klaus Haslinger on behalf of the Authors (01 Mar 2016) Author's response Manuscript

ED: Publish subject to technical corrections (02 Mar 2016) by Jan Seibert

AR by Klaus Haslinger on behalf of the Authors (02 Mar 2016) Manuscript

Short summary

Gridded fields of daily max. and min. temperatures for the Austrian domain are used to calculate ET0 based on a re-calibrated Hargreaves method. Newly derived, station-based calibration parameters, with Penman–Monteith ET0 as a reference, show a distinct altitude and seasonal dependence. Theses features are used to interpolate the new calibration values in space and time onto the temperature grids. The ET0 is then calculated based on the entire gridded temperature data starting back in 1961.