## 5 Conclusions  
In this paper, we analyzed the response of the WUE changes to regional climate and vegetation cover changes during the annual period of 2001 to 2020 using the PML GPP and ET datasets. Our results showed that the multi-year mean WUE value of the Loess Plateau is 1.24 g C mm\({}^{-1}\) H\({}_{2}\)O, and the spatial pattern of the WUE varies among seasons, with the mean WUE size being ranked as summer > autumn > spring in the different seasons. The WUE rates of all vegetation types showed a decreasing trend with the increase in drought index values, and it was most obvious in summer. The magnitude of the response rate of the WUE to drought for each vegetation type was ranked as: grassland > forest > scrub > crop.  
The annual average WUE increase rate for the Loess Plateau was 0.02 g C mm\({}^{-1}\) H\({}_{2}\)O a\({}^{-1}\), of which 93.36% of the area showed an increasing trend. Due to the difference in precipitation temperature in the different seasons, this led to the changes in WUE rates in different seasons still showing a big difference, and the mean WUE increase in summer was more significant. The NDVI was the dominant factor affecting the spatial and temporal variations in WUE in the Loess Plateau. The correlation between the NDVI and WUE was the strongest in summer. The change pattern of the NDVI values with the increase in drought index rates showed the same change pattern as for the growth trend of the WUE. The ecosystem WUE was negatively correlated with the precipitation temperature in drier regions, but throughout the summer, the precipitation boosted the WUE. In comparison to forest and crop regions, the link between the WUE and temperature in grassland and scrub areas was more sensitive to the values of the drought index, but there was also a threshold effect. Thus, for the arid and semi-arid Loess Plateau regions, these findings deepen our understanding of the carbon and water coupling mechanisms of different vegetation types, providing important ideas for the sustainable development of vegetation on the Loess Plateau and future ecological restoration management and governance approaches.  
Conceptualization: R.M.; Data curation: R.M. and D.W.; Formal analysis: [PERSON] and S.L.; Visualization: X.C. and S.W.; Writing--original draft preparation: [PERSON] and H.W.; Writing--review and editing: [PERSON] and X.Y. 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, 42141007; 41671362; 52274169 and the Special Funds for the Transformation of Scientific and Technological Achievements in the Inner Mongolia Autonomous Region 2021 CG0045.  
The GPP and ET datasets are available from Google Earth Engine (GEE) at [[https://developers.google.com/earth5-Sengine/datasets/catalog/CAS_IGSNRR_PML_V2_v017](https://developers.google.com/earth5-Sengine/datasets/catalog/CAS_IGSNRR_PML_V2_v017)]([https://developers.google.com/earth5-Sengine/datasets/catalog/CAS_IGSNRR_PML_V2_v017](https://developers.google.com/earth5-Sengine/datasets/catalog/CAS_IGSNRR_PML_V2_v017)) (accessed on 20 July 2022). The NDVI datasets are available from GEE at [[https://developers.google.com/earth5-Sengine/datasets/catalog/MODIS_006_MOD13A1](https://developers.google.com/earth5-Sengine/datasets/catalog/MODIS_006_MOD13A1)]([https://developers.google.com/earth5-Sengine/datasets/catalog/MODIS_006_MOD13A1](https://developers.google.com/earth5-Sengine/datasets/catalog/MODIS_006_MOD13A1)) (accessed on 20 July 2022). The meteorological data were downloaded from the National Meteorological Science Data Center at [[http://data.cma.cn/](http://data.cma.cn/)]([http://data.cma.cn/](http://data.cma.cn/)) (accessed on 20 July 2022).  
The authors declare no conflict of interest.