Comparing Palmer Drought Severity Index drought assessments using the traditional offline approach with direct climate model outputs

Yang, Yuting; Zhang, Shulei; Roderick, Michael L.; McVicar, Tim R.; Yang, Dawen; Liu, Wenbin; Li, Xiaoyan

doi:https://doi.org/10.5194/hess-24-2921-2020

Articles | Volume 24, issue 6

https://doi.org/10.5194/hess-24-2921-2020

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

https://doi.org/10.5194/hess-24-2921-2020

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

Articles | Volume 24, issue 6

Research article

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03 Jun 2020

Research article | Highlight paper |

| 03 Jun 2020

Comparing Palmer Drought Severity Index drought assessments using the traditional offline approach with direct climate model outputs

Yuting Yang, Shulei Zhang, Michael L. Roderick, Tim R. McVicar, Dawen Yang, Wenbin Liu, and Xiaoyan Li

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Final revised paper (published on 03 Jun 2020)
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Preprint (discussion started on 03 Feb 2020)
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Interactive discussion

Status: closed

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

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SC1: 'Comment on Yang et al.', Conrad Jackisch, 06 Feb 2020
- AC1: 'Reply to hess-2019-701-SC1', Yuting Yang, 25 Feb 2020
RC1: 'Referee comment', Anonymous Referee #1, 24 Feb 2020
- AC2: 'Reply to the three anonymous reviewers', Yuting Yang, 16 Mar 2020
RC2: 'Review of hess-2019-701', Anonymous Referee #2, 03 Mar 2020
- AC2: 'Reply to the three anonymous reviewers', Yuting Yang, 16 Mar 2020
RC3: 'Excellent innovative study - freeing the PDSI from potential evapotranspiration by using directly simulated evapotranspiration, runoff, and soil moisture', Anonymous Referee #3, 09 Mar 2020
- AC2: 'Reply to the three anonymous reviewers', Yuting Yang, 16 Mar 2020
AC2: 'Reply to the three anonymous reviewers', Yuting Yang, 16 Mar 2020

Peer-review completion

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

ED: Publish subject to revisions (further review by editor and referees) (13 Apr 2020) by Adriaan J. (Ryan) Teuling

AR by Yuting Yang on behalf of the Authors (21 Apr 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Apr 2020) by Adriaan J. (Ryan) Teuling

RR by Anonymous Referee #3 (24 Apr 2020)

Suggestions for revision or reasons for rejection

This revision addressed my comments almost entirely. I recommend publication pending the following minor revisions. The first suggested revision is an aspect I overlooked last review, but the other suggested revisions are simply follow-ons to changes the authors made in response to previous round of comments (mine and others'.) All should be very quick to implement.

22-24: This is an important thought but is never fleshed out in the body text with full citations, though aspects of it are mentioned. I think it's worth including a paragraph or a few sentences in the body (specifically, the introduction) about this contradiction, so the reader knows where in the published literature to verify each of the claims you are stating (i.e. that greening occurred over the last few decades, that runoff had little systematic change in the last few decades, that slight runoff increases are projected for future, and that large greening is projected for future.) Otherwise the abstract has un-cited statements.

In general, this contradiction is a powerful motivation for the rest of the paper, but almost seems to be forgotten about in the body text (except for the specific aspect about future runoff projections) after a very strong opening here in the abstract.

66: more specifically, this should say "right-hand column of Fig 1" or similar. In general, I would check through the whole paper and make sure that each time Fig 1 is called out, it mentions the appropriate column(s).

194: The increases may "diminish", but they are still quite noticeable and widespread. Most interesting is that even when using PDSI_CMIP5 and PDSI_PM[CO2] (4b-c), there are *still* far more land areas with increases (yellow, orange, red) than with decreases (blue shades.) This should be pointed out explicitly.

I.e. it should be pointed out that moving to PDSI_CMIP5 or PDSI_PM[CO2] reduces the magnitude of the drought frequency increase, but apparently does not reduce the very *widespread* distribution of drought frequency increase compared to drought frequency decrease.

Fig 4: I'm not quite sure how to interpret the trend units (month yr-1) ? Shouldn't it be (month yr-2) , i.e., the trend-per-year in the number of months-per-year that exceed the given threshold? (Analogous to Fig S1?) Or do I misunderstand what you mean.

In general, all the trends in the figures would be easier to understand if they were given per *century* of trend, rather than per year or per decade. I.e. multiply Fig 3 by 100 and change unit to PDSI/century, multiply Fig 4 by 100 and change unit to (month/year)/century (I think?), multiply Fig S1b,c by 100 and change unit to (mm/year)/century, multiply Fig S4 by 10 and change unit to PDSI/century. This is optional but I think helps readers a lot to understand the magnitude.

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RR by Anonymous Referee #1 (27 Apr 2020)

ED: Publish subject to minor revisions (review by editor) (27 Apr 2020) by Adriaan J. (Ryan) Teuling

AR by Yuting Yang on behalf of the Authors (28 Apr 2020) Author's response Manuscript

ED: Publish as is (07 May 2020) by Adriaan J. (Ryan) Teuling

AR by Yuting Yang on behalf of the Authors (07 May 2020)

Short summary

Many previous studies using offline drought indices report that future warming will increase worldwide drought. However, this contradicts observations/projections of vegetation greening and increased runoff. We resolved this paradox by re-calculating the same drought indices using direct climate model outputs and find no increase in future drought as the climate warms. We also find that accounting for the impact of CO₂ on plant transpiration avoids the previous overestimation of drought.