## 4 Discussion  
The water balance equation proposed by [PERSON] (1979) for estimating basin evapotranspiration is accurate, involves few parameters, and is easy to apply, the P, R in the equation can be obtained from ground-based observations, \(\Delta\)SW can only be obtained with GRACE (Gravity Recovery and Climate Experiment) at present, so the use of the water balance equation for estimating evapotranspiration is usually used within the basin and on monthly or even coarser time scales. Since the water balance does not consider the spatial distribution of evapotranspiration, to further verify the accuracy of the model, the water balance results, PT-JPL model calculations, and the evapotranspiration results obtained from the MODIS evapotranspiration product MOD16A2 for the same period were compared: MODIS_ETa was 512.3 mm, which was lower than WB_ETa, with an absolute error of 31 mm and a relative error of 6%; MODIS_ETa was also lower than PT-JPL_ETa, with an absolute error of 11.5 mm and a relative error of 2%. It can be seen that the evapotranspiration results obtained by the three methods were very close, which also indicates that the PT-JPL model is applicable in the Yliuo River Basin.  
The study of [PERSON], [PERSON] (2018) showed a general decreasing trend in the middle and lower reaches of the Yellow River Basin, which is consistent with the findings of this paper; however, the study of [PERSON] (2018) showed that the evapotranspiration in the upper, middle and lower reaches of the Yellow River Basin were in an increasing state. The differences in the length of time series and data sources make the actual spatial and temporal variability of evapotranspiration different. Extending the time series is more beneficial to grasp the actual spatial and temporal variation of evapotranspiration in the watershed. The PT-JPL model does not involve the calculation of evapotranspiration from artificial objects near rivers, but there are many artificial objects in river networks and systems, and this part of evapotranspiration should be taken into account in future studies. In addition, we did not take into account the effect of processes such as sublimation on the measurement of evapotranspiration when exploring the intra-annual variation of evapotranspiration, which is an area for improvement in future studies.  
Actual regional evapotranspiration is influenced by a combination of factors, such as solar radiation, temperature, humidity, wind speed, subsurface changes, and precipitation. Climate elements change the water vapor transport environment/influence energy supply and determine the maximum amount of actual evapotranspiration possible, precipitation influences water supply conditions and water supply capacity, and vegetation, as a carrier of interception and transpiration processes, further influences the magnitude of actual evapotranspiration (2018).  
From the results of the correlation analysis, the actual Eta showed a good correlation with NDVI, precipitation, and temperature. A good correlation between NDVI and evapotranspiration was also found in the study of [PERSON], [PERSON] (2018). In this paper, the best correlation was with temperature, which indicated that the ETA in the Yliuo River Basin might be most influenced by air temperature; however, the change trend of ETa and temperature was opposite and the same as that of precipitation, which indicated that the main factor that might influence ETa was precipitation. In summary, the combination of all influencing factors caused changes in evapotranspiration. However, the actual evapotranspiration is influenced by vegetation, climate, soil, topography, human activities, etc. The mechanisms and drivers of evapotranspiration changes need to be studied in more depth in order to better grasp the evolution of evapotranspiration.