## 4 Discussion  
### Analysis of Influencing Factors of Evopotranspiration in Rice Paddies  
Evopotranspiration (ET) plays a crucial role in water resource management in rice paddies. With the growth of data, computing power, and storage capacity, the utilization of machine learning models for predicting ET has gradually increased [27; 28]. [PERSON] et al. [29] found that the XGBoost model significantly enhances the performance in predicting Penman-Monteith reference evapotranspiration (ET\({}_{0}\)) compared with the RF model. [PERSON] et al. [30] used the same models, XGBoost and RF, as this study did, based on three years of experimental data to predict crop evapotranspiration. The results revealed that XGBoost outperformed RF in predicting crop evapotranspiration, consistent with the findings of this study regarding XGBoost's prediction of rice evapotranspiration. In addition, [PERSON] et al. revealed the order of importance of input factors obtained from the XGBoost model. Similarly, this study used the XGBoost model to rank the importance of the input factors in predicting rice ET.  
Previously, [PERSON] et al. [31] indicated that radiation was the dominant factor for rice ET through multiple stepwise regression analyses. [PERSON] et al. [32] found that solar radiation was the most critical factor in California and all its climatic zones. They used eight factors (TA, SW, VPD, PA, WS, NDVI, SWC, and DeltaTA) as factors for rice ET modeling, except for the absence of SWC at the US-Twt site. From the results of the gain value obtained from the XGBoost model, radiation showed the most significant effect on ET. The decisive reason why these studies found that radiation plays such a large role in predicting evapotranspiration is that radiation provides the energy required for rice evapotranspiration [33].  
In addition, [PERSON] et al. [34] also found that the influence of radiation was excellent; the second and third factors were VPD and TA. They found that VPD was significantly better than TA at JP-MSE and US-Twt sites, consistent with the previously mentioned studies, and while at IT-Cas sites, TA had better feature importance than VPD. The former may be due to the influence of rice during the growth process by rough irrigation and water supply. When the leaf surface is humid and the ambient temperature is high, a higher VPD usually occurs. In this case, the rice may need to release water more quickly to adapt to environmental conditions, resulting in larger evapotranspiration [35]. The latter is that the ET of the IT-CAS site was more sensitive to temperature than VPD, which may be due to the fact that the site has a lower temperature, resulting in a relatively small VPD. However, the significant change in temperature makes TA have a greater effect on rice evapotranspiration.  
Except for SW, TA, and VPD, other factors were less important in predicting evapotranspiration in rice paddies. In some water-scare areas, soil moisture was the dominant factor of evapotranspiration [36], while this paper studies the evapotranspiration of rice paddies, which maintains a certain height of water layer for a long time through irrigation during the planting process, so soil moisture performance was poor in this study.