## 4 Discussion  
### Climatic Factors Drive Monthly ET Influenced by Elevation  
Altitude strongly influenced climatic conditions and consequently influenced ET and its sensitivity to climatic factors [49]. In order to facilitate analysis and statistics, this paper divided the elevation of the YRB into regions (Table 2). As analyzed in Section 3.2, the correlation between climatic factors (T, SR, and P) and ET showed a spatial evolution from west to east, and the elevation of the YRB was high in the west and low in the east. From the perspective of monthly changes, the area of the positive correlation between ET and T gradually increased from February to June and then fluctuated and decreased (Figure 19d). Figure 19a showed that the area proportion of the region with significant positive correlation between T and ET showed a decreasing trend from elevation I to XI, and it increased again in the region of elevation XII. This indicated that the sensitivity of ET to T decreased with the increase in altitude, being consistent with [PERSON] et al. 's study in which the sensitivity of ET\({}_{\text{O}}\) to T was negatively correlated with altitude at the annual  
Figure 18: Spatial regions of ET driven by climatic factors in the YRB from 2001 to 2020 at the monthly scale. A\(-\)M represent 13 sub-basins of the YRB, which are as follows: the Jinsha River Basin; the mountainous areas in the upper reaches of Dadu River and Jialing River; the confluence area of Sichuan Basin; the main stream area in the upper\(-\)middle reaches of the Yangtze River; the Wujiang River Basin; the middle reaches of the Yangtze River; the confluence area of Nanyang Basin; the Jianghan\(-\)Dongting Lake Plain; the Dongting Lake Basin; the mountainous area of Ganjiang River Basin; the Poyang Lake Plain; the confluence area of Chao Lake and the plain along Wanjiang River, and the confluence area of the Yangtze River Delta. and seasonal scales [49]. It should be noted that the area proportions closed to 0% in the range of elevation V to XI, indicating a significant positive correlation between ET and T in very few areas within these regions in individual months. This could explain the spatial distribution and area of the regions with significant positive correlation between ET and T in Section 3.2.1, which varied from month to month, mainly related to altitude. By studying the performance of the region with significant positive correlation between ET and SR at the monthly scale (Figure 19d), it was found that the area of this region gradually increased from March to July and then fluctuated and decreased from August to January of the next year, but it was significantly higher in February than in January and March. In terms of spatial distribution (Figure 19b), the regions with significant positive correlation between ET and SR were usually found in the low-elevation region, i.e., the proportion of area in this region was above 90% in the range of elevation I to III, after which its trend decreased in the range of elevation III and IX, and the proportion of area in the range of elevation IX to XII was generally low, below 20%. This was probably due to the extended duration of snow cover and convective clouds at higher altitudes that may lead to the reduction in absorbed shortwave radiation [50], making ET less sensitive to SR, which could explain the spatial variation in the region with significant positive correlation between ET and SR in Section 3.2.3, mainly related to altitude. Generally speaking, topographic conditions have obvious influence on precipitation distribution [51], so the relationship between the effect of P on monthly ET and elevation should also be considered.