###### Abstract  
Investigating the attributions of evapotranspiration (ET) and gross primary production (GPP) changes is of great importance for regional, sustainable water resources and ecological management in semi-arid regions. Based on the simulation conducted during 2000-2019 by improving water-carbon coupling Distributed Time Variant Gain Model, the trends of ET and GPP were estimated and the driving factors were identified via 10 experimental scenarios in the water source area of the Xiong*an New Area in North China. The results show significant increases both in ET and GPP by 2.4 mm/a and 6.0 gC/m\({}^{2}\)/a in the region, respectively. At the annual scale, increasing precipitation dominates the ET uptrend. Air temperature, humidity and the interactive effects also contribute to the ET uptrend, and the contributions are 12.8%, 2.0% and 2.3%, respectively, while elevated atmospheric CO\({}_{2}\) concentration (eCO\({}_{2}\)) and solar dimming lead to ET changes of about \(-\)7.2% and \(-\)12.4%, respectively. For the GPP changes, the increase in GPP is mainly caused by eCO\({}_{2}\), increasing precipitation and rising temperature with the contributions of 56.7%, 34.8% and 27.8%, respectively. Solar dimming, humidity and windspeed contribute \(-\)6.8%, \(-\)4.8% and \(-\)3.5% of the GPP changes. Compared to climate change, land use and cover change has smaller effects on both ET and GPP for the few changes in land coverage. At the seasonal scale, ET and GPP increase to a greater extent during the growing season in spring and summer than in autumn and winter. Precipitation, temperature and eCO\({}_{2}\) are generally the main causes for ET and GPP changes. Meanwhile, the decreasing humidity and rising temperature are dominant factors for ET and GPP increases, respectively, in winter. Furthermore, solar dimming has strong effects on ET reduction in autumn. The contribution of the interactive effects is much higher on a seasonal scale than annual scale, contributing to considerable decreases in ET and GPP in spring, increases in ET in autumn and winter, and an increase in GPP in winter. This study highlights the importance of considering water-carbon coupling on the attributions of ET and GPP changes and the differentiation of the effects by the abovementioned influential factors at annual and seasonal scales. * 2022 20  
great importance to regulate the terrestrial carbon sink in terrestrial ecosystems [5]. In semi-arid regions, ET is the major flux occurring in the water cycle and accounting for most of the precipitation; furthermore, GPP also plays an important role in the inter-annual variability of the global carbon sink [6]. Researches show that increased ET and GPP lead to decreased runoff, subsequently resulting in water shortages and drought aggravation in semi-arid region [7]. Droughs are very common in these regions [8]. Besides, ET and GPP have a strong coupling relationship with each other through the stomatal pathway controlling transpiration and photosynthesis [9], which makes the water and carbon changes more complex, posing challenges to drought control. Therefore, it is important to investigate the ET and GPP changes and their attributions in these regions for catchment water resources management. Recently, researchers have shown that ET has increased globally by 10% between 2003 and 2019 and precipitation is increasingly classified as ET [10]. Meanwhile, GPP has also demonstrated an increment globally during the past years [11]. The estimated results also show that changes in ET and GPP vary between different regions in the semi-arid region [12; 13]. These spatial heterogeneous patterns have been widely attributed to different climate variables [14], CO\({}_{2}\) fertilization [15], land use and cover change (LUCC) [1].