| 13 Oct 2025
An improved GRACE-derived groundwater storage anomaly (igGWSA) dataset over global land with full consideration of non-groundwater components based on current new datasets
Abstract. Accurate quantification of global groundwater storage anomaly (GWSA) is imperative for global water security and socio-economic sustainability. The Gravity Recovery and Climate Experiment (GRACE) satellite has emerged as a prevailing methodology for estimating GWSA. However, oversimplification of non-groundwater components potentially compromised its accuracy in most previous studies. Here we present an improved GRACE-derived GWSA dataset at the global scale, namely igGWSA, with full consideration of non-groundwater components including glaciers, snow, permafrost, lakes, reservoirs, surface runoff, profile soil moisture (PSM), and plant canopy water based on current new datasets. In particular, PSM was generated based on Catchment Land Surface Model and random forest algorithm. igGWSA demonstrated strong agreement with well-observed groundwater level and model-simulated GWSA in five globally recognized hotspots of groundwater depletion. Compared to igGWSA with full consideration, simplified estimation would lead to misinterpretations of groundwater storage variations in glacier-covered regions, giant lakes, and deep-soil areas, highlighting the necessity of comprehensively accounting for non-groundwater components in estimating GWSA, especially under a changing environment. igGWSA dataset is publicly available on Zenodo through https://doi.org/10.5281/zenodo.16871689 (Wang et al., 2025).
In this study titled ‘An improved GRACE-derived groundwater storage anomaly (igGWSA) dataset over global land with full consideration of non-groundwater components based on current new datasets’, the authors consider various surface water changes that are likely to contribute to the GWSAnomaly based on GRACE data. They show that glacier melting, change in global lakes storage among others, contribute to the GWSA signal and that ignoring these contributions could lead to misinterpretation of ground water depletion or recharge trends. The overall content is well suited for this journal. As the scientific validity appears sound, my feedback mostly concerns the readability, organisation and clarification of the manuscript/content. Some remarks:
Specific comments:
LN22: “… would lead to misinterpretations of groundwater storage variations in glacier-covered regions” – …misinterpretation of GW storage? You detail some of the misinterpretations in the last sections but you could also briefly state some here.
LN26: “https://doi.org/10.5281/zenodo.16871689 (Wang et al., 2025)” – The data is provided as a .mat file. Matlab is not freely available, making the data un-accessible to many. Can the authors provide the dataset in an open format; e.g. in .nc or a multi-band .tiff?
LN133: ‘Snow water equivalent simulations from seven reanalysis products’ - which metric is used for the SWE ensemble-wightedaverage used in this study? average, median … ?
LN161-178: ‘2.2.7. Profile soil moisture (PSM) …’ – since you do not present the other datasets/variables with this much detail, this block of text could be well suited for the supplements (only keep a short summary here)
LN180: ‘meteorological variables, and vegetation index’ - You mention the meteorological variables and indices used later in the text (i.e. precipitation and ndvi) but you should also list them here.
LN181: ‘…selected as predictor variables’ - Why was evapotranspiration (which is a main component of the water cycle, thus a likely driver of water storage anomalies) not used as one of the predictors/covariates ? there are many global ET products that are freely available
LN208: Why not use the much simpler nearest neighbour. Unlike bilinear, it does not create new data (i.e. keeps the original data as-is)?
LN219,220: ‘generate ensemble simulations‘ - do you mean to ‘generate the weighted average from the ensemble simulations’?
‘… (Fig. 1, Text S5’ - In Text S5 in the supplementary document you write ‘𝜎𝑖 is the error variance of the 𝑖th dataset’ – 𝜎𝑖 is the standard deviation; change 𝜎𝑖 to 𝜎𝑖2, which is the variance
LN280: ‘To quantify the impacts of incomprehensive considerations of non-groundwater components, five kinds of non-improved GWSA were further estimated as listed below.’ - Seems arbitrary; any justifications for selecting these 5 and not any other combinations ?
LN298: ‘five globally recognized hotspots of groundwater depletion, …’ – reference/citation needed
LN304-306: ‘Accordingly, point-scale data were first converted into pixel-scale by averaging observations of wells located in the specific grid cell. Then in situ GWL and GWSA estimation at a 0.5° X0.5° resolution were upscaled to obtain basin-averaged time series.’ - not enough information for the reader to determine how this was done
LN342: ‘loess and chernozem zones worldwide’ – reference needed
LN372: ‘Given this, evaluation of interannual trends in PSM was carried out additionally’ – grammar: rephrase or remove ‘additionally’
LN380-387: section 4.2.1 - Why do you compare the era5-land-SMS289 (and other SMS) estimates to SMSimproved? Some justification needed here.
LN417: ‘Validation of igGWSA against GWDin situ and GWSAWGHM’ - Since you also compare your igGWSA with the GWSA_WGHM, can you also provide other metrics for a more exhaustive comparison, e.g. bias …
LN419-…: ‘section 4.3.2: Uncertainty analysis’ - recall the metric used to quantify the uncertainty here. Is it GTCH, similar to how uncertainties in PSM are quantified?
LN440: ‘This pattern was found in Region 5, 9, and 12’ - igGWSA in region 12 does not appear to show a decreasing trend
LN447: ‘Therefore, absence of glaciers would inevitably ‘ - not clear …rephrase
LN456-458: interesting observations. Can you expound a bit on this.’ - Interesting. Can you elaborate a bit on this?
Chapter 4: What about permafrost? The authors seem to have left out presenting results on effects of ignoring permafrost when estimating the GWSA
LN522: ‘Mann-Whitney U test…’ - Reference needed or provide a bit more details in the supplements