Questions about the accuracy of calculations

[dingjy0714]

I tried to use this code to calculate the daily evapotranspiration data of a farmland during the growing period of the crop.

However, there is a big difference between the calculated results and the ETMonitor product. R-squared can reach more than 0.6 in June and July. Surprisingly, other months (April, May, and August) have an R-squared of less than 0.01, and their RMSE values are also high.

Is this problem caused by the TSEB model or this code? And what should I do to to improve the accuracy?

Looking forward to your reply!