###### Abstract  
An accurate assessment of the spatial-temporal variations in regional net ecosystem productivity (NEP), water use efficiency (WUE), and carbon use efficiency (CUE) are vital for understanding the water-carbon cycle. We analyzed the spatial-temporal patterns of the NEP, WUE, and CUE in the middle reaches of the Yellow River (MRYR) from 2001 to 2022, and the factors that influenced them using remote sensing data, NEP estimation models, and various statistical methods. The results indicate that the recovery of the ecosystem in the MRYR is a result of the combined effects of climate change and human activities. Climate change in the MRYR led to warming and humidification from 2001 to 2022. The NEP, WUE, and CUE were characterized by increasing trends, with average growth rates of 7.75 gC m\({}^{-2}\)a\({}^{-1}\), 0.012 gC m\({}^{-2}\) mm\({}^{-1}\)a\({}^{-1}\), and 0.009a\({}^{-1}\), respectively. For four vegetation types, the interannual rates of change were, in descending order, grassland, cropland, shrubs, and forest. Spatially, the NEP, WUE, and CUE showed significant regional heterogeneity, increasing from the northwest to the southeast. Based on an analysis of the interannual anomalies, precipitation accumulation contributed to carbon sink accumulation. The correlation of the NEP, WUE, and CUE with the drought severity index (DSI) was high, and their correlation with precipitation showed latitudinal zonality, which suggests that precipitation (PRE) is the main climatic factor influencing the water-carbon cycle in the MRYR rather than temperature (TEM). There were 67,671.27 km\({}^{2}\) of land that changed use during 2001-2022, and 15.07 Tg of NEP was added to these areas. NEP; WUE; CUE; climate variability; land cover change; middle reaches of the Yellow River  
15 July 202430 August 202  
primary productivity (GPP) minus the total ecosystem's respiration over a given period of time [9]. In general, ecosystems are carbon sinks when the NEP is positive and vice versa [10; 11; 12]. Carbon sinks are spatially influenced by factors such as vegetation type, climate, human activities, etc., while changes in carbon sinks over time are primarily influenced by changes in climatic factors [13]. In relatively arid regions, the temperature and precipitation are the main controlling factors [13]. Solar radiation has the greatest impact on carbon sinks in humid and semi-humid regions [14]. Thus, it is clear that the degree of response of vegetation to environmental factors and human activity varies in different regions [15; 16]. Different vegetation types respond differently to climate change due to their physiological structure and function [17; 18]. Thus, understanding the impacts of climate on land cover change can lead to more effective land management strategies. The carbon use efficiency (CUE) and water use efficiency (WUE) are significant parameters used for evaluating carbon sequestration and water use in vegetation [19]. The CUE is the proportion of carbon used by organisms to form biomass to the total carbon they take up [20]. A higher carbon use efficiency means that organisms release less carbon, which is conducive to carbon stabilization and long-term sequestration. According to related studies, the CUE can be subdivided into the vegetation CUE (CUEa), microbial CUE (CUEh), and ecosystem CUE (CUEe) [21]. Both the CUEa and CUEh are interconnected through aboveground and belowground apomic material [22], which is expressed as the CUEe, the ecosystem CUE. The CUEe is calculated by the formula NEP/GPP, which reflects the carbon sequestration potential of the vegetation in an ecosystem [23; 24]. In this study, the concept of the CUEe is used to analyze the study area. The WUE is the rate of carbon sequestration per unit of water consumption [25]. The WUE is calculated using different methods depending on the purpose [26]. Here, the WUE is defined as NEP/ETa, with ETa being the actual evapotranspiration. The CUE was initially thought to be converging to 0.5 [27].