Systematic bias of Tibetan Plateau snow cover in subseasonal-to-seasonal models

Li, Wenkai; Hu, Shuzhen; Hsu, Pang-Chi; Guo, Weidong; Wei, Jiangfeng

doi:https://doi.org/10.5194/tc-14-3565-2020

Articles | Volume 14, issue 10

The Cryosphere, 14, 3565–3579, 2020

https://doi.org/10.5194/tc-14-3565-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Cryosphere, 14, 3565–3579, 2020

https://doi.org/10.5194/tc-14-3565-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 10

Research article 29 Oct 2020

Research article | 29 Oct 2020

Systematic bias of Tibetan Plateau snow cover in subseasonal-to-seasonal models

Wenkai Li et al.

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Final revised paper (published on 29 Oct 2020)
Preprint (discussion started on 15 Jun 2020)

Interactive discussion

Status: closed

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

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RC1: 'Comment for “Systematic bias of Tibetan Plateau snow cover in subseasonal-to- seasonal models”by Hu & Li.', Anonymous Referee #1, 19 Jun 2020
- AC1: 'Response to Anonymous Referee #1', Wenkai Li, 26 Aug 2020
RC2: 'Review of Hu, S. and Li, W.', Anonymous Referee #2, 21 Jul 2020
- AC2: 'Response to Anonymous Referee #2', Wenkai Li, 26 Aug 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (28 Aug 2020) by Mark Flanner

AR by Wenkai Li on behalf of the Authors (28 Aug 2020) Author's response Manuscript

ED: Reconsider after major revisions (further review by editor and referees) (11 Sep 2020) by Mark Flanner

AR by Wenkai Li on behalf of the Authors (18 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Sep 2020) by Mark Flanner

RR by Anonymous Referee #1 (24 Sep 2020)

RR by Anonymous Referee #2 (02 Oct 2020)

Suggestions for revision or reasons for rejection

The authors have addressed most of my comments, and substantially revised and improved the manuscript.

I believe that there may be an incorrect statement that possibly needs to be changed. I hence recommend a minor revision.

1) Concerning the initialization of snow in the ECWMF system, the authors mention: “The snow mass is initialized by the ECMWF Land Data Assimilation System (LDAS). The snow initialization relies on a land surface synoptic report and national ground observations of the snow depth available on the Global Telecommunications System (GTS), as well as on the Interactive Multisensor Snow and Ice Mapping System (IMS) snow cover information.”

I believe that this is correct for the operational real-time S2S forecasts, but the authors seem to use the reforecasts (stated L74). In the reforecasts, a re-analysis is used for initialization of the land states.
Taking from the webpage cited by the authors “If the initialization of the LSM for re-forecasts deviates from the procedure for forecasts, please describe the differences. The re-forecasts initialization is based on ERA-Interim and ERA-Interim/Land datasets, while the real-time forecasts are based on the IFS operational initial conditions of the ENS/EDA systems.” It is unclear to me if the re-analysis that is used now, is based on the ERA5 system or still ERA-Interim.

Please clarify these points if necessary, for the sake of correctness (although this will not change the results).

In any case, note that the ECMWF LDAS would not use IMS in high altitude regions, such as the Tibet, nor incorporate in-situ snow depth measurements in that region.

2) I couldn’t find information about the ensemble size of the forecasts for each prediction system (how many members were analysed or else averaged in the ensemble mean, e.g. the ECMWF S2S reforecasts have 11 members); this should be put at beginning of section 2.1.

3) My original comment was on the short length of the period over which the forecasts are evaluated (1999-2010, around 10 years). The authors have now doubled the length of the period covered by the WRF simulations to cover 1999-2020, but it is appears that the forecasts have only been evaluated over 10 years (e.g. the period 1999-2020 could have been covered). As I stated in my original review, it appears that the biases are quite strong and systematic, and I realise that adding another 10 years may entail a lot of computational work. At least, a word of caution in the summary about the short period over which the forecasts are evaluated is warranted.

Suggestions for wording
L199: occur at a regional scale
L247: such an overestimation persists throughout the model integration
L294: I believe you mean the *decline of the SAT*, not the growth (Fig 10b) (?)
L306: this sentence is a repeat of line L286 in the same section.

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ED: Publish subject to minor revisions (review by editor) (12 Oct 2020) by Mark Flanner

AR by Wenkai Li on behalf of the Authors (20 Oct 2020) Author's response Manuscript

ED: Publish subject to technical corrections (20 Oct 2020) by Mark Flanner

AR by Wenkai Li on behalf of the Authors (21 Oct 2020) Author's response Manuscript

Short summary

Understanding the forecasting skills of the subseasonal-to-seasonal (S2S) model on Tibetan Plateau snow cover (TPSC) is the first step to applying the S2S model to hydrological forecasts over the Tibetan Plateau. This study conducted a multimodel comparison of the TPSC prediction skill to learn about their performance in capturing TPSC variability. S2S models can skillfully forecast TPSC within a lead time of 2 weeks but show limited skill beyond 3 weeks. Systematic biases of TPSC were found.