## 3 Results
### Correlation Analysis between ET and Driving Factors
#### 3.2.2 Correlation Analysis between Precipitation and ET  
As shown in Figure 8a, the correlation coefficient between ET and P ranged from \(-\)0.86 to 0.75, with a spatially averaged correlation coefficient of \(-\)0.25, which meant the correlation between ET and P was more often negative. The area with significant and extremely significant positive correlation between ET and P accounted for 2.34% in the study area, and the area with extremely significant positive correlation accounted for 0.49%; they were concentrated in the source of the YRB (Figure 8b). The areas with significant and extremely significant negative correlation accounted for 25.43% of the total area, and the regions with extremely significant negative correlation accounted for only 10.16%, mainly distributed in the middle and lower reaches of the YRB and the southwest part of sub\(-\)basin A. However, there were more areas with non-significant correlation between ET and P accounting for 72.23% of the YRB.  
Figure 6: Spatial distribution map (**a**) and significance test results (**b**) of correlation coefficient between T 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 7: Correlation significance test results of monthly T 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.  
Similarly, the heterogeneity of the correlation between ET and P for the 12 months in the YRB was significant (Figure 9). There were few areas where P was positively correlated with ET, and most of them were distributed in the headwaters and upper reaches of the YRB, with the highest proportion of 12% in January and then gradually decreased until July, which was the lowest in the whole year, accounting for only 0.02% of the total basin area, and then fluctuated below 4%. The area with significant positive correlation between P and ET mainly existed from January to April of the year with low T in time and was mainly distributed in the headstream of the YRB in spatial pattern.  
As a whole, P was mainly negatively correlated with ET, and the proportion of the regions with negative correlation was the lowest in January, accounting for only 1.11%, then fluctuated up to July, reaching 45.2%, and then fluctuated down from August to December. The regions with negative correlation were mainly in the middle and lower reaches of the YRB, while they were also distributed in the upper reaches in July and August.