# Precipitation-Use Efficiency and Its Conversion with Climate Types in Mainland China
## 3 Results
### Driving Force of PUE Changes and Its Corresponding Conversion Characteristics  
Fluctuations in environmental factors have a significant effect on the PUE. Here, we selected Tmean, Rn, U, Rh, and soil moisture (SM) as influencing factors to characterize the energy, dynamic, and water statuses, respectively. Regression models between regional  
Figure 10: Precipitation-use efficiency (PUE) trend (1960–2017) and (**a**) distribution of average values and trends in the sub regions and (**b**) +indicates that the trend was significant at the 0.05 level. Figure 9: Spatial distribution of mean precipitation-use efficiency (PUE) in China during 1981–2010. environmental factors and PUE were established (Table S1). Based on the trends and sensitivity analysis, the contribution of each factor to the PUE change was obtained. Figure 11 shows the trends of environmental factors from 1960 to 2017. Over the past 58 years, Tmean in China exhibited a significant increasing trend. Air-temperature increases in the arid region and transition zone are particularly evident. Rn, U, and Rh exhibited decreasing trends. Among them, Rn decreased most significantly in the eastern transition zone and the humid region, especially in Beijing-Tianjin-Hebei and the lower reaches of the Yangtze River, which is closely related to increased aerosols in these areas [78]. U also decreased most significantly in the eastern transition zone and east of the humid region. In addition, U exhibited significant decreasing trends in most of the arid regions. Rh change is more complicated. Rh in the western Tianshan Mountains, which are located in an arid region, exhibited an increasing trend because the climate in the region tends to be warm and humid [50]. Rh decreased in most of the rest of the country. SM changes differed from east to west. The arid region and western transition zone exhibited significant SM increases, whereas the Middle Eastern transition zone and humid region exhibited SM decreases. Overall, soil tended to become arid. PUE changes in different regions caused by changes in environmental factors are shown in Figure 12. In the arid region, PUE increased by 6.5% over the past 58 years. The Tmean increase reduced the PUE by 9.3%. The SM increase and U decrease increased the PUE by 8.4% and 6.1%, respectively. Rn and Rh increased the PUE by 1.3 and 1.9%, respectively. SM was the main driving force of regional PUE increases. In the humid region, PUE decreased by 3.5% over the past 58 years. The relative change rates of PUE caused by changes in Rn, U, Tmean, Rh, and SM were \(-\)15.3, 13.0, \(-\)3.2, \(-\)1.3, and 1.6%, respectively. Rn changes were the main driving force of regional PUE decreases. Over the  
Figure 11: Trends of each environmental factor from 1960 to 2017, (**a**) Tmean, (**b**) Rn, (**c**) U, (**d**) Rh, (**e**) SM, +indicates that the trend was significant at the 0.05 level. past 58 years, atmospheric aerosols in humid regions increased significantly, whereas net radiation decreased significantly [78]. As a result, vegetation photosynthesis is inhibited, vegetation productivity decreases, and PUE decreases accordingly. The impact of climate factors on PUE in the transition zone is more complicated. From the regional average sequence, the positive contribution of the Tmean increase and the U decrease to PUE offset the adverse effects of the Rn and SM decreases, which makes the PUE change insignificant. However, the PUE change in the transition zone exhibited obvious regional differences. The PUE decrease in the western plateau area was dominated by a significant SM increase. The PUE increase in the central regions was mainly due to the positive effect of a U decrease. PUE in the eastern and northeastern regions of the transition zone was dominated by Rn, which means that a significant Rn decrease can reduce the PUE. Overall, the PUE trend was dominated by water in the northern and arid regions and by energy in the southern and humid regions of China.