## 3 Results
### Correlation Analysis between ET and Driving Factors
#### 3.2.3 Correlation Analysis between Solar Radiation and ET  
The correlation coefficient between ET and SR ranged from \(-\)0.58 to 0.90, with a spatially averaged correlation coefficient of 0.32, which meant the correlation between ET and SR was more often positive (Figure 10a). According to statistics 33.61% of the area with significant and extremely significant positive correlation between ET and SR, and 20.15% of the area with extremely significant positive correlation was concentrated in the central region of the YRB (Figure 10b). The areas with significant and extremely significant negative correlation were very few, accounting for only 0.81%, among which the areas with extremely significant negative correlation tended to be close to 0, accounting for only 0.06% of the area, mainly distributed in the UYRB. However, the areas with non\(-\)significant correlation between ET and SR accounted for 65.57% of the YRB.  
Figure 8: Spatial distribution map (**a**) and significance test results (**b**) of correlation coefficient between P and ET at the annual scale in the YRB. 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.  
Figure 9: Correlation significance test results of monthly P and ET in the YRB. 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.  
The correlation between ET and SR in the YRB showed significant differences in 12 months (Figure 11), and the correlation between the two was more similar to that between ET and T. The correlation between SR and ET is non\(-\)significant in most regions of the YRB in January, with the area accounting for about 89.83%. At the same time, the area where the two were significantly positively correlated was smaller than the area where they were significantly negatively correlated and was mainly distributed in the lower reaches of the YRB. With the change in months, the areas with significant positive correlation also gradually expanded to the middle and upper reaches (except March) and reached the peak in August, when the areas with significant positive correlation occupied about 77.69% of the YRB. After that, with the increase in the months, the area where the two were positively correlated also began to gradually decrease, while in January of the following year it began to gradually expand again, and the correlation between the two showed a more obvious cyclical change. In addition, the areas with significant negative correlation between ET and SR were mostly located in the UYRB, but in August and September, they were concentrated in the source of the YRB.