## 5 Conclusions  
In this study, based on the MODIS vegetation GPP and ET products, we estimated and quantitatively analyzed the characteristics of the annual-scale spatial and temporal variations in multi-year vegetation GPP, ET, and WUE in Gansu Province from 2000 to 2020; further, combined with air temperature, precipitation, vapor pressure deficit, and soil moisture, we investigated the response of vegetation WUE to the natural environment elements. Our key findings are presented below.  
(1) The average values of vegetation WUE, GPP, and ET in Gansu Province from 2000 to 2020 were 1.46 gC-mm\({}^{-1}\).m\({}^{-2}\), 510.22 gC\(\cdot\)m\({}^{-2}\), and 343.68 mm, respectively, and their spatial distributions were high in the southeast and low in the northwest, in close relation to the distribution of vegetation in the region.  
(2) In the considered 20 years, the vegetation WUE in Gansu Province showed a slowly decreasing trend in general. It decreased from 1.81 gC\(\cdot\)mm\({}^{-1}\).m\({}^{-2}\) in 2000 to 1.51 gC\(\cdot\)mm\({}^{-1}\).m\({}^{-2}\) in 2020, with a reduction rate of 16.57%. There were significant differences in the WUE of different vegetation types, among which forest WUE was the highest and grassland WUE the lowest.  
(3) The prediction of the WUE trend in Gansu Province was performed by using the rescaled extreme difference method, and the Hurst index was 0.45, which means that the future trend in WUE has a long-term correlation with that of 2000-2020 and is opposed to it; the time series thus exhibits inverse persistence, indicating that the vegetation WUE in Gansu Province will likely undergo a gradual increase in the future.  
(4) In general, precipitation was the main factor influencing the change in vegetation WUE in Gansu Province, followed by VPD, temperature, and soil moisture. There is a large amount of natural vegetation in the areas outside the Hexi Corridor, and the amount of precipitation affects the change in vegetation NPP, thus influencing vegetation WUE. However, in the Hexi Corridor Plain and a large number of cultivated farmland areas in eastern Gansu Province, vegetation WUE and precipitation were negatively correlated, which suggests that anthropogenic disturbances will likely weaken the effect of climatic factors on vegetation WUE.  
Conceptualization, N.X. and L.W.; methodology, N.X., and J.H.; software, L.W., and T.Y.; data curation, K.Z.; writing--original draft preparation, N.X.; writing--review and editing, N.X. and B.Z.; supervision, G.D.; funding acquisition, G.D. All authors have read and agreed to the published version of the manuscript.  
This research study was funded by National Natural Science Foundation of China, grant No. 41971268.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
This work was partially supported by National Natural Science Foundation of China (No. 41971268). The datasets were provided by the National Tibetan Plateau/Third Pole Environment Data Center ([[http://data.tpdc.ac.cn](http://data.tpdc.ac.cn)]([http://data.tpdc.ac.cn](http://data.tpdc.ac.cn))), and data support was received from \"National Earth System Science Data Center, National Science & Technology Infrastructure of China. ([[http://www.geodata.cn](http://www.geodata.cn)]([http://www.geodata.cn](http://www.geodata.cn)))\".  
The authors declare no conflicts of interest.