Analysis of Spatiotemporal Groundwater-Storage Variations in China from GRACE

Round 1

Reviewer 1 Report

Your manuscript presents an analyis of groundwater storage (GWS) variations over China using GRACE-based terrestrial water storage (TWS) and model ouptuts over 2003 to 2019. There several key issues which need to be solved.

About the method. You used the classical removal of the different water storage anomalies to the GRACE-based TWS to isolate GWS. For this, GLDAS model outputs were used. As you mentionned in 2.2.2, GLDAS does not simulate surface water storage (SWS). This means that over large part of China (Yangtze and Yellow Rivers among others, large lakes in Tibet and other regions), GWS is the sum of GWS and SWS. This needs to be solved.

An average was performed to fill the gap between GRACE and GRACE-FO. What is the impact of this operation on trends estimates ?

About the data. There are a lot of GRACE data and products available. CSR made available level-1 GRACE data, level-2 spherical harmonics, level-3 filtered harmonics products but also mascons products, which one do you used ?

I stopped reading at the beginning of the results. Figures 2 and 3a are very difficult to read. You need to make them clearer.

About the introduction. It seems a summary of the one from Frappart and Ramillien (2018). As it is a review paper, you could cite it after « Thanks to therelease of GRACE satellite data, it is possible to retrieve groundwater data in  combination  with  other  auxiliary  data », lines 51-52.

Frappart, F.; Ramillien, G. Monitoring Groundwater Storage Changes Using the Gravity Recovery and Climate Experiment (GRACE) Satellite Mission: A Review. Remote Sens. 2018, 10, 829. https://doi.org/10.3390/rs10060829

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

At first, it is worth mentioning that this paper deals with an interesting hydrogeological issue regarding the analysis of spatiotemporal groundwater-storage variations in China using GRACE and GRACE-FO terrestrial water-storage anomalies and GLDAS data. The subject is within the topics of the Water Journal. The manuscript is clearly written following a structure that contains analysis and elaboration results sufficiently documented.

It would be quite interesting and informative to present some essential information/data focusing on the clarification of the hydrogeological regime of the aquifer systems in the study area, such as: basic geological information, type of aquifers (unconfined/confined), and if possible, range of specific yield/storage coefficient values depending on each type of aquifer.

Considering all the above, my recommendation is that the manuscript should be accepted for publication after minor revision.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for a,swering my questions. Figure 2 and 3a are still very difficult to read.

GRACE-data allows to spatialize the groundwater changes but it would be important to validate your results using in-situ data to give more confidence in you estimates.

Author Response

Thank you for that. Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Thank you for your answers. I have nothing more to add.