###### Abstract
The studies also show that the dominant factors on ET and GPP changes are always different from continental to regional scales at different timescales, considering one or two of the factors including different climate variables, elevated CO\({}_{2}\) and land-use change [16; 17; 18; 19]. In semi-arid ecosystems, water availability is the main limit for ecosystem productivity and water-carbon is strongly coupled in this region. Understanding the changing characteristics and the driving factors are of great importance for these regions. Besides, it is still unclear which climate variable or land-use change has positive effects or negative effects on ET and GPP changes due to previously inconsistent conclusions in different regions. Meanwhile, as we know, the causality between the factors and water-carbon fluxes at the relatively coarse spatiotemporal resolution may not reflect the substantial mechanisms in the sub-grid, which may be unable to provide sufficient support for the catchment water-resources management. Therefore, further investigation into the reasons behind ET and GPP changes in catchment scales at annual and high time resolution is still needed, considering multiple influence factors in semi-arid regions. Nowadays, two kinds of models are commonly used to estimate ET and GPP and their attributions, i.e., the elastic-coefficient statistical-based model [20] and physical process-based model [21; 22]. The elastic-coefficient statistical based model is usually based on regression analysis [23] or Budyko hypothesis [24]. The physical process-based model combined with remote sensing data is the most popular method and presents the advantages of providing a useful framework to incorporate specific responses to altered environmental conditions [25]. So far, because vegetation growth is not well considered in most traditional hydrological models, these models still have poor ET simulation [26]. In contrast, ecological models perform quite well in GPP simulation but always lack detailed hydrological processes. Subsequently, the attributions analysis in GPP and ET are mostly conducted without considering the water-carbon interactions. Ecohydrological models considering the water-carbon cycles alongside the rainfall-runoff relationship could well consider the interactions between vegetation dynamics and hydrological processes, which can be better used to quantify the effects of climate variables, CO\({}_{2}\) enrichment and human activities on the changes in ET and GPP. Recently, several studies have focused on attribution analyses for both ET and GPP using ecohydrological models [27; 28; 29]. The Xiong'an New Area is located in the semi-arid region in North China, which is a typical over-utilized water resources region [30]. Investigating the hydrological and ecological changes and their driving factors is of significance for sustainable water-resources management in this region. So far, several studies have shown dramatic hydrological changes and quantified the effects of the two factors, i.e., climate variability and human activities, focusing on the streamflow reduction into the downstream [31; 32]. Some studies analyze the effects of climate change and vegetation change on ET and concluded that it is mainly caused by climate change [33]. However, to our knowledge, there are still only a few studies conducted on the attributions of both ET and GPP changes considering multiple factors in this region. In this study, the improved coupling water-carbon DTVGM ecohydrological model was used to simulate the ET and GPP in the six catchments of the water source area of the Xiong'an New Area and then the contributions of multiple influence factors including climate variables, eCO\({}_{2}\) and underlying land cover change and their interactive effects on ET and GPP were quantified at annual and monthly timescales based on ten experimental scenarios.