Uncertainty of simulated groundwater recharge at different global warming levels: a global-scale multi-model ensemble study

Reinecke, Robert; Müller Schmied, Hannes; Trautmann, Tim; Andersen, Lauren Seaby; Burek, Peter; Flörke, Martina; Gosling, Simon N.; Grillakis, Manolis; Hanasaki, Naota; Koutroulis, Aristeidis; Pokhrel, Yadu; Thiery, Wim; Wada, Yoshihide; Yusuke, Satoh; Döll, Petra

doi:https://doi.org/10.5194/hess-25-787-2021

Articles | Volume 25, issue 2

https://doi.org/10.5194/hess-25-787-2021

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

https://doi.org/10.5194/hess-25-787-2021

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

Articles | Volume 25, issue 2

Research article

|

19 Feb 2021

Research article |

| 19 Feb 2021

Uncertainty of simulated groundwater recharge at different global warming levels: a global-scale multi-model ensemble study

Robert Reinecke, Hannes Müller Schmied, Tim Trautmann, Lauren Seaby Andersen, Peter Burek, Martina Flörke, Simon N. Gosling, Manolis Grillakis, Naota Hanasaki, Aristeidis Koutroulis, Yadu Pokhrel, Wim Thiery, Yoshihide Wada, Satoh Yusuke, and Petra Döll

Download

Final revised paper (published on 19 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 08 Jun 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC1: 'Review', Anonymous Referee #1, 02 Jul 2020
- AC1: 'Response to RC1, RC2, and RC3', Robert Reinecke, 28 Aug 2020
RC2: 'Review of "Uncertainty of simulated groundwater recharge at different global warming levels: A global-scale multi-model ensemble study” by Robert Reinecke et al.', Anonymous Referee #2, 05 Jul 2020
- AC1: 'Response to RC1, RC2, and RC3', Robert Reinecke, 28 Aug 2020
RC3: 'Review', Anonymous Referee #3, 14 Jul 2020
- AC1: 'Response to RC1, RC2, and RC3', Robert Reinecke, 28 Aug 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) (30 Sep 2020) by Philippe Ackerer

AR by Robert Reinecke on behalf of the Authors (30 Sep 2020) Author's response Manuscript

ED: Publish subject to revisions (further review by editor and referees) (02 Oct 2020) by Philippe Ackerer

ED: Referee Nomination & Report Request started (05 Oct 2020) by Philippe Ackerer

RR by Anonymous Referee #4 (13 Nov 2020)

Suggestions for revision or reasons for rejection

This paper uses a multi-model ensemble of global hydrological models and global circulation models to analyze the uncertainties in groundwater recharge projections under three different RCPs. The authors further analyze how accounting for changes in CO2 impact groundwater recharge response to a changing climate.
3 reviewers have provided their insights in the first round. I strongly agree with reviewer 3 in the sense that the study is at its early stage and there are several things to be addressed. The reviewer raised some important and key points that the authors missed to address. I will advise the authors to address these issues (e.g. the use of groundwater recharge and the large uncertainties of their results). The authors would rather focus on fluxes and water storages which is what these models are actually simulating or clarify that they are showing an effective recharge, not the actual recharge, which is much more complex.
Reviewer 3 also suggested comparing GHMs against fully integrated hydrologic models that simulate recharge processes, but the authors failed to do so. It would be great to compare in some areas how their models performed compared to the integrated hydrologic models. These models are now run on a continental scale. The model outputs could also be compared to some global datasets to ensure that they are at least consistent with observations at this scale and resolution.
The topic of this paper is relevant to the community. The authors mostly presented a bunch of results without explaining in detail why we are observing the changes and what is driving these changes, the most expecting part of this kind of study. In addition, the authors miss the opportunity to discuss the setting up of their models (initial conditions, parameterization, etc.), model validation is also an important step in modeling.
Understanding what is driving the processes and the observed changes should be the key output of this study, this will advance not only our knowledge on the uncertainties associated with the simulated groundwater responses to climate change but also how can we reduce these uncertainties.
The authors have done tremendous work to develop such a global modeling framework. I would recommend the authors to thoroughly revise their paper, discuss the use of groundwater recharge, provide some explanations in the uncertainties they are observing, and compare these uncertainties to the ones associated with evapotranspiration.
Below some specific comments:

1. The table added in the revised manuscript is very helpful. Nonetheless, I will make the table clearer without text. The authors should also clearly discuss the differences in the processes resolved by these models.
2. The authors should dedicate a section to discuss the types of data they use to build their models. Did they use the same datasets for all these models? How did they initialize their models? Before jumping into model comparisons, one needs to clearly understand the differences in the model parameters and initializations. The authors discuss the climate simulations but since their paper is focused on groundwater recharge, it is the groundwater models and their uncertainties in computing the recharge that needs to be discussed.
3. The outcome of the climate simulations should also be discussed in the paper to have an idea of how key forcing variables change over time and have a clear view of what should be expected in terms of groundwater changes.
4. The authors discuss the trends they observed in the figures but there is no explanation about the drivers of these trends. One can expect to know why a region sees a high increase in groundwater recharge and other regions not. The sensitivity of a region to these changes should be discussed in this paper. These sensitivities are linked to the physical parameters of the region, these parameters aren’t presented to it is really hard to understand the response of the region.
5. Differences observed between different models should also be discussed and explained, these differences may be related to the processes that these models are reproducing among others.
6. Investigating the impact of CO2 on groundwater is a very important topic, and there is a lot of interest in the community to understand to what extent accounting for CO2 in hydrology impact the projected changes in groundwater. Nonetheless, as for the other results, the authors should provide an explanation about why a particular area sees a high impact and other areas not.
7. Given the types of models (not fully integrated hydrologic models) that the authors used, the uncertainties they are observing are likely tied to the uncertainties in the estimation of evapotranspiration. It would be great to discuss evapotranspiration first then the impacts on recharge and analyze how these two uncertainties differ.

Hide

RR by Anonymous Referee #5 (31 Dec 2020)

Suggestions for revision or reasons for rejection

The manuscript deals with an important issue: the uncertainty on future groundwater recharge (GWR) due to climate change. This uncertainty is estimated using eights different global hydrological models (GHMs) and the outputs of four global circulation models (GCMs). I will not go into the debate of using GHMs instead of fully integrated physically based hydrologic models (IPHMs), even if the uncertainty would have been better estimated by using models with significant differences in their philosophy and conceptions. GHMs are valuable tools and the provided results are a good estimate of uncertainty in GWR at a global scale under this framework. Therefore, the manuscript is of a very good scientific level and suitable for publication in HESS.
I suggest revision before publication for the following two reasons:
1. The reliability of the GHMs is not convincingly described. A section should be dedicated to the description of the ability of GHMs to simulate real situations on different sites over the world. It should not be an exhaustive description of GHMs applications to real sites, but some examples found in the literature of different GHMs simulations of large scale watersheds under different climatic conditions. If GHMs are not able to estimate water balances including GWR properly at the time scale used in this work and over the last decades, the interest of this work appears to be limited.
2. I missed GHMs parameters. Please provide an insight on models parameterization.

Minor comments
The last sentence in the abstract is awkward and has to be more specific. You cannot write ‘additional research on simulating groundwater processes in GHMs is necessary’ and use GHMs to estimate recharge.

Hide

ED: Publish subject to minor revisions (review by editor) (06 Jan 2021) by Philippe Ackerer

AR by Robert Reinecke on behalf of the Authors (15 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (19 Jan 2021) by Philippe Ackerer

AR by Robert Reinecke on behalf of the Authors (19 Jan 2021) Author's response Manuscript

Short summary

Billions of people rely on groundwater as an accessible source of drinking water and for irrigation, especially in times of drought. Groundwater recharge is the primary process of regenerating groundwater resources. We find that groundwater recharge will increase in northern Europe by about 19 % and decrease by 10 % in the Amazon with 3 °C global warming. In the Mediterranean, a 2 °C warming has already lead to a reduction in recharge by 38 %. However, these model predictions are uncertain.