How to calculate groundwater storage change (GWSA)?

[weixiaoxun]

Hello! Professor! How to simulate GWSA using CWATM? In a previous post, I saw you mention using storGroundwater minus unmetDemand as GWSA. Is this correct? I calculated GWSA using this approach, but the results differ significantly from GRACE-GWSA. Could you please provide specific instructions on how to simulate GWSA using CWATM? Thank you.

[mikhailsmilovic]

Guten Morgen weixiaoxun, for comparison with GRACE, we would use
total water storage (tws) minus unmet demand (unmetDemand)
assuming limitAbstraction = False

This video demonstrates comparing CWatM and GRACE for the Danube basin but does not include subtracting by unmetDemand (in the Danube, there is relatively no fossil water use)

Feel free to include your specific example and results 🛰
The previous post referring to this question: #98

[weixiaoxun]

Guten Morgen！Thank you for your response. Previously, I used the CWATM model to simulate TWSA and compared it with GRACE-TWSA. However, based on the YouTube video, I used "limitAbstraction = True." After watching #98, if I want to simulate groundwater storage (GWS), should I subtract unmetDemand from storGroundwater?
This image includes the GWS obtained by subtracting unmetDemand from storGroundwater (not sure if it is correct), but it shows significant differences in trend compared to the other two results. Professor, could you please confirm if I am doing it correctly?

[mikhailsmilovic]

Guten Tag! When comparing with GRACE, we need to use total water storage—anomalies in total water storage, not groundwater storage, are being measured.

If limitAbstraction = True, would you show tws anomalies compared with GRACE?
If limitAbstraction = False, would you show tws - unmetDemand anomalies compared with GRACE?

What region is being modelled here? 🌏

[weixiaoxun]

Hello mikhailsmilovic,
Figure 1 shows GRACE-TWSA and CWatM-TWSA when limitAbstraction = True.

Figure 2 represents the modeling region, which is the southern part of mainland China.

In the previous discussion, we talked about simulating GWSA using TWSA-SMSA-SWEA-CWSA obtained from GLDAS, and comparing it with CWatM's simulated storGroundwater-unmetDemand to derive CWatM-GWSA. I'm not entirely clear on whether storGroundwater-unmetDemand represents GWS. I kindly request clarification on this matter.

Best wishes
xiaoxun

[mikhailsmilovic]

Guten Morgen, yes for groundwater storage anomalies, storGroundwater - unmet demand (assuming limitAbstraction = False) is correct

[weixiaoxun]

Thank you very much for answering my questions,Professor mikhailsmilovic!

Best wishes!