# Precipitation-Use Efficiency and Its Conversion with Climate Types in Mainland China
## 5 Conclusions  
Based on the improvement of the ET\({}_{\text{a}}\) model, this study characterized the responses of ET\({}_{\text{a}}\), NPP, and PUE to climate change in different climatic regions of China, revealed the PUE conversion characteristics with the precipitation distribution, and clarified the driving force of PUE changes in different climate regions. The main conclusions are as follows:  
The improved ET\({}_{\text{a}}\) model fully reflects the energy limitation on ET\({}_{\text{a}}\) in humid regions, and the estimated ET\({}_{\text{a}}\) is more reasonable and reliable. The distribution of ET\({}_{\text{a}}\) and NPP in China shows a gradually increasing trend from northwest to southeast, and the trends of ET\({}_{\text{a}}\) and NPP both change from an increase to a decrease from the arid to the humid region. ET\({}_{\text{a}}\) and NPP fluctuations in arid regions are mainly controlled by water, and the increase in precipitation and soil moisture is the main reason. ET\({}_{\text{a}}\) and NPP in humid regions are mainly controlled by energy. ET\({}_{\text{a}}\) in the transition zone is affected by both water and energy, and regional differences in ET\({}_{\text{a}}\) and NPP changes in the transition zone are large. There was a conversion zone of PUE in mainland China. Arid and humid regions had the lowest PUE, and the transition zone with annual precipitation of 200-600 mm had the highest PUE. In the past 58 years, PUE in arid regions has exhibited an increasing trend, whereas PUE in the transition zone generally exhibited a slightly decreasing trend. PUE displayed a decreasing trend in most of the humid regions. PUE changes in arid regions are dominated by water conditions, whereas changes in energy in humid regions largely determine PUE changes. The transition zone is the conversion zone where the prevailing factor transitions from water to energy. PUE changes are caused by the interaction of energy, water, and dynamic factors. Among them, soil moisture plays the most prominent role, followed by temperature and wind velocity. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs14102467/s1](https://www.mdpi.com/article/10.3390/rs14102467/s1)]([https://www.mdpi.com/article/10.3390/rs14102467/s1](https://www.mdpi.com/article/10.3390/rs14102467/s1)), Table S1: Regression equation between environmental factors and PUE in each sub regions (annual averaged air temperature (Tmean), net radiation (Rn), wind velocity (U), relative humidity (RH), and soil moisture (SM), respectively). Conceptualization, P.Y. and Q.Z. ; methodology, P.Y., S.W., J.Y. and H.Z. ; software, S.W., W.W. and J.W. ; formal analysis, S.W. and P.Y. ; writing--original draft preparation, S.W. ; writing--review and editing, S.W., P.Y. and Q.Z. ; visualization, S.W., X.R. and J.W. ; funding acquisition, P.Y. and S.W. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grant No. U2142208, 41975016), the Basic Research Innovation Group Project of Gansu Province (Grant No. 20 JR5 RA121), the Natural Science Foundation of Gansu Province (Grant No. 21 JR7 RA698), and the Foundation of drought Meteorological Science Research (Grant No. IAM202001). Not applicable.