## 5 Conclusions  
WUE is a crucial indicator of the relationship between terrestrial carbon and water cycles, as well as an effective variable reflecting the response of productivity to water availability. This study adopted remote sensing data and meteorological data to examine variation characteristics of WUE and its response mechanism to human activity and climate change. The main findings can be summarized as follows:  
1. The interannual change of GPP, ET, and WUE all showed significant increasing trends, with GPP showing a significantly larger increase than ET and WUE. Spatially, GPP, ET, and WUE showed an increasing trend. WUE showed increasing and decreasing trends in approximately 70% (22.35%) and 30% (2.63%) of the study area, respectively. Areas with significant increases were mainly distributed in the Horqin sandy land and the Mu Us sandy land, while areas with significant and slight decreases were concentrated in the central part of the Xilin Gol league and the Da Hinggan Ling Mountains in the northeast. 2. The seasonal WUE values followed the order summer (1.77 gC m\({}^{-2}\) mm\({}^{-1}\)) > autumn (1.36 gC m\({}^{-2}\) mm\({}^{-1}\)) > winter (0.78 gC m\({}^{-2}\) mm\({}^{-1}\)) > spring (0.40 gC m\({}^{-2}\) mm\({}^{-1}\)). This phenomenon may be related to seasonal differences in GPP and ET. 3. The mean values of GPP, ET, and WUE were higher in the broadleaf forest, coniferous forest, meadow steppe, shrubs, and cropland than in other vegetation types, whereas desert steppe ecosystems had the lowest. However, we discovered that typical steppe contributed the most to GPP, ET, and WUE IAV. While the coniferous forest contributed the least or negatively to GPP, ET, and WUE IAV. This phenomenon may be associated with the physiological structure, area distribution, and survival condition of vegetation types. Figure 12: Land use spatial change maps for each league or city in Inner Mongolia from 2000 to 2020. (4) The sensitivity analysis of WUE to GPP and ET revealed that WUE was more sensitive to GPP than ET. The increase of WUE was mainly driven by GPP. Its contribution was 59.36%, accounting for 83.82% of total pixels, which covered most of the central and western regions and the eastern and western parts of Hulun Buir. The contribution of ET was 40.64%, accounting for 16.18% of the total pixels, which were scattered in the Da Hinggan Ling Mountains, the northern part of the Horqin sandy land, and the northern part of the Mu Us Sandy land. (5) Human activities and climate change were found to be the two main forces driving the variability of WUE, with contributions of 53.52% and 46.48%, respectively. Human activities were the primary cause of WUE changes and their positive effects were significantly stronger than their negative effects. Among climate factors, precipitation was the primary climate factor affecting WUE changes in Inner Mongolia, followed by temperature and solar radiation. This study sheds light on the distribution characteristics of carbon and hydrology, as well as the response of carbon-water coupling to climate change and human activity in arid and semi-arid regions. It offers guidance on ecological environmental management and water resource utilization in water-limited regions. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs14215422/s1](https://www.mdpi.com/article/10.3390/rs14215422/s1)]([https://www.mdpi.com/article/10.3390/rs14215422/s1](https://www.mdpi.com/article/10.3390/rs14215422/s1)). Figure S1: Spatial pattern of annual average WUE in Inner Mongolia from 2001 to 2020. (a) Spring, (b) Summer, (c) Autumn, and (d) Winter. Figure S2: Degrees of land use dynamics for each league or city in Inner Mongolia from 2000 to 2020. Table S1: Land use transfer matrix in 2000-2020 (km\({}^{2}\)). Conceptualization, Formal analysis, Writing--original draft, L.M. ; Methodology, Writing--reviewing & editing, S.T. ; Investigation, Validation, Writing--review & editing, S.Y. ; Project administration, Funding acquisition, Y.B.