Results of water yield & groundwater values

My English is not very good, the expression may be incomplete, please forgive me!
When I run the Annual water yield module analysis, the results obtained are very close to the groundwater results (38.8 billion), and very different from the surface water results (227.7 billion) (the above two data are the sum of the water yield grid of the whole region multiplied by the grid area of 30 * 30)
However, I have read a lot of literature, and we all compare and calibrate with the total amount of water resources or surface water. My precipitation and evapotranspiration data are downloaded from published data, which should be no problem. The biophysical table and Z parameter have little influence on the results. I don’t know whether my result is right or wrong now. Can I calibrate it with groundwater?
I look forward to your reply!
Thank you very much.

Hi @Wei,

The Annual Water Yield model is a pretty simple model and does not handle any routing, in-stream processing, or groundwater flow. What type of area or climate are you running the model in? Wet, dry, mountainous? Have you double checked the units of the data you are using are what the model expects? When you say “surface water results (227.7 billion)”, what units is that?

~ Doug

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Thank you very much for your reply!
My research area is located in the southeast of the Qinghai Tibet Plateau in China. All the units I mentioned above are m ³。
All my original data are officially published, so I don’t think my results should have problems. I try to adjust the Z parameter and biophysical table, but they have very little influence on the results. Adjusting them can’t let me get the ideal value.
I have read a lot of literature, and have not yet understood what data is required for water yield calibration, so I am not sure whether my results are wrong or whether I should choose other data for calibration!
We look forward to your reply!
Thank you~

Hi @Wei -

As @dcdenu4 noted, the Annual Water Yield model does not explicitly model groundwater. The model assumes that all precipitation that falls on the area eventually enters streams within a year, but does not specify how, or when, it flows to the stream. So the modeled annual water yield value consists of both surface runoff and sub-surface flow (such as dry-season baseflow).

To calibrate the total water yield value, we use long-term annual average stream flow data, which usually comes from stream gauges. A bit more information is provided in the User Guide Appendix 2: Calibration of Water Yield.

If you have done a sensitivity analysis to find the most influential parameters, and changing those parameters does not cause the model to create output that comes close to observed data, then it is possible that this model is not a good fit for your area. For example, if most of the water in streams comes from groundwater, and the amount of water that flows from groundwater is based on very long-term processes (not directly tied to annual precipitation) then the model is unlikely to produce results that match observed data.

~ Stacie

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Well, it seems that I have to change my research area!
Thank you~