Something fishy going on? Evaluating the Poisson hypothesis for rainfall estimation using intervalometers: results from an experiment in Tanzania

de Villiers, Didier; Schleiss, Marc; ten Veldhuis, Marie-Claire; Hut, Rolf; van de Giesen, Nick

doi:https://doi.org/10.5194/amt-14-5607-2021

Articles | Volume 14, issue 8

https://doi.org/10.5194/amt-14-5607-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-14-5607-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 8

Research article

|

17 Aug 2021

Research article |

| 17 Aug 2021

Something fishy going on? Evaluating the Poisson hypothesis for rainfall estimation using intervalometers: results from an experiment in Tanzania

Didier de Villiers, Marc Schleiss, Marie-Claire ten Veldhuis, Rolf Hut, and Nick van de Giesen

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Final revised paper (published on 17 Aug 2021)
Preprint (discussion started on 22 Jun 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Testing the Poisson hypothesis for rainfall homogeneity and stationarity', Anonymous Referee #1, 12 Oct 2020
- SC1: 'Thank you for commenting more detailed response to follow later', Didier de Villiers, 16 Oct 2020
- AC1: 'Reply on RC1', Didier de Villiers, 11 Mar 2021
RC2: 'Review of manuscript AMT-2020-174 “Something fishy going on? Evaluating the Poisson hypothesis for rainfall estimation using intervalometers: results from an experiment in Tanzania”, submitted to AMT by Didier de Villiers et al.', Remko Uijlenhoet, 19 Oct 2020
- AC2: 'Reply on RC2', Didier de Villiers, 11 Mar 2021

Peer-review completion

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

AR by Didier de Villiers on behalf of the Authors (22 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (04 May 2021) by Piet Stammes

RR by Piet Stammes (22 May 2021)

Suggestions for revision or reasons for rejection

Regarding the author's response to RC1:
The response to the second and third comments, "No changes", is not acceptable. The authors should clarify the manuscript and add the references according to the reviewer's suggestions.

Regarding the author's response to RC2, there is a remaining question:

On l.181-182 of the revised manuscript the authors state: "The Dmin value of 0.8 mm for the intervalometer means that the instrument is likely to miss a lot of small drops and underestimate rainfall rates". This effect is presumably even stronger for the employed disdrometer, which has a minimum detectable drop size of 1 mm (l.339). The authors take this truncation effect into account in the derivation of a self-consistent lambda-R relation in their revised manuscript (Eq.8). It should be noted, however, that the rainfall rate R derived by inverting this relation (l.151) does not correspond to the true rainfall rate, but rather to the effective rainfall rate a disdrometer with a minimum detectable drop size of 1 mm would "see". The same holds presumably for estimates of R based on their power law model for No (Eq.9), even though "the experimentally determined power law parameterization resulted in the best estimates of the co-located tipping bucket rainfall amount for both the intervalometer (overestimate of 12%) and the disdrometer (underestimate of 4%)." (l.324-325). The fraction of the raindrop size distribution below 1 mm also contributes to the rainfall rate, although this contribution becomes relatively less important for higher rainfall rates (for which smaller raindrops are less abundant). It is not clear to me if the authors have taken this effect explicitly into account when deriving rainfall rates from their disdrometer or their intervalometer observations.

In addition, there are two minor editorial remarks:

- The reference to Guyot et al. (2019) in the reference list (l.483 of the revised manuscript) should be updated to: Hydrol. Earth Syst. Sci., 23, 4737–4761, 2019, https://doi.org/10.5194/hess-23-4737-2019.

- The title of the reference to Ulbrich (1983) in the reference list (l.540 of the revised manuscript) should start with "Natural" rather than "Numerical".

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ED: Publish subject to minor revisions (review by editor) (27 May 2021) by Piet Stammes

AR by Didier de Villiers on behalf of the Authors (15 Jun 2021) Author's response Manuscript

ED: Publish as is (06 Jul 2021) by Piet Stammes

AR by Didier de Villiers on behalf of the Authors (13 Jul 2021) Author's response Manuscript

Short summary

Ground-based rainfall observations across the African continent are sparse. We present a new and inexpensive rainfall measuring instrument (the intervalometer) and use it to derive reasonably accurate rainfall rates. These are dependent on a fundamental assumption that is widely used in parameterisations of the rain drop size distribution. This assumption is tested and found to not apply for most raindrops but is still useful in deriving rainfall rates. The intervalometer shows good potential.