The result of Annual Water Yield

What is the issue or question you have?

(1) The calculated correlation coefficient between water yield and precipitation is only 0.48, which seems a little low. According to the existing research results in the study area, the correlation between water yield and precipitation should be higher. What might be the problem?
(2) There is a big difference between the actual evapotranspiration in the calculation results and the distribution trend of evapotranspiration of the synthesized MOD16A2 product. So, is the estimated water yield still authentic?

What do you expect to happen?

(1) Hope to find out the reason why the correlation between water yield and rainfall is not high.
(2) How to verify the authenticity of the estimated actual evapotranspiration?

What have you tried so far?

I checked all the input data and found no problems.

Attach the logfile here:

Thank you very much for your attention and answer.

Hi @vivian -

Remember that the Annual Water Yield model is an extremely simple representation of very complex hydrological processes. Water is not routed down the landscape, no baseflow or groundwater interactions are included, etc. So it is unlikely to provide results that are precise, compared with observed data.

Also, as with any hydrologic model, if you have observed data, we highly recommend using it to calibrate the model, which helps the model produce results that are closer to reality.

Regarding MOD16A2, I haven’t used this dataset, but it looks like an 8-day composite. Is there an annual average version of this that you’re comparing to the AWY results? AWY operates on an annual time scale, and it would not be appropriate to compare an 8-day composite to annual AET.

~ Stacie

1 Like

First, I’m very sorry for responding to your message so slowly.
For the above problems,the water yield results in (1) above have been adjusted according to the total surface water resources in the study area, but the correlation coefficient with the input precipitation grid data is only 0.48. The guess may be related to the large error caused by the interpolation of precipitation data from site data. The MOD16 data in the above (2) is an annual mosaic data, which is different from the actual evapotranspiration calculated by the model in spatial distribution. I still can’t find out the reason.
Finally, I sincerely thank you for your patient answer, which made me have a deeper understanding of this module.

Hi @vivian -

It is certainly possible that the rainfall interpolation contributes to the discrepancy. Do you have many sites around your study area? Are they well-spaced, and include any mountainous areas? Do you have any other spatial dataset to compare your interpolation against?

For MOD16, is it actual evapotranspiration, potential ET or reference ET? Just making sure that you’re comparing actual ET to actual ET. If the MOD16 data is, say, reference ET, it does not include the effects of vegetation, which actual ET does.

~ Stacie

There are indeed fewer sites around the study area, including mountainous areas. I am looking for other data sets for comparison.
Thank you very much for your detailed answer. I really appreciate it.