## 1 Introduction  
Vegetation is widely distributed in the world and plays an irreplaceable role in the global carbon cycle, water cycle, and material-energy transfer [1, 2]. In addition, vegetation also plays a crucial part in regulating the climate, conserving soil and water, and maintaining the stability of ecosystems [3]. Vegetation converts solar energy into biomass through photosynthesis [4, 5]. Net primary productivity (NPP) quantifies the total amount of organic matter accumulated by vegetation through photosynthesis and amount remaining after deducing autotrophic respiration per unit of time and space, which reflects vegetation growth and ecosystem health [6], and it is a key factor in evaluating the carbon sink and ecological regulation behavior of terrestrial ecosystems [7, 8]. The offset of anthropogenic carbon dioxide (CO\({}_{2}\)) emissions by increasing terrestrial NPP is considered to be one of the most environment-friendly and economical ways to mitigate climate change and the greenhouse effect [9, 10]. Given the significance of NPP in the global carbon budget and the need for carbon neutral targets on the global scale [11], it is critical to explore the spatiotemporal dynamic characteristics of NPP and its response mechanisms to the driving factors [12]. Changes in NPP are influenced by multiple drivers, including environmental and climatic factors, as well as human activities [13, 14, 15]. Global climate change has significantly affected ecosystem productivity by altering ecosystem processes, including plant photosynthesis, respiration, phenology, and the rate of soil organic carbon decomposition [16; 17; 18]. Human activities, such as land use/land cover (LULC) change and urbanization, directly change the structure, processes, and functions of terrestrial ecosystems [6; 19], which consequently affect terrestrial NPP [20; 21; 22]. Recently, many studies have been conducted on understanding the response of NPP to different factors at different temporal and spatial scales, ranging from inter-monthly or inter-annual to millennial, as well as from landscape and regional to global [6; 14; 22; 23; 24; 25], with methods such as correlation analysis [26], regression [27], principal component analysis [28], sensitivity analysis [29], etc. However, there are still uncertainties in the relative impacts of climate change and human activities on NPP, although several studies have focused on these issues and attempted to explain the response of NPP to climate change and anthropogenic perturbations [7; 13]. Previous studies have taken two main approaches to assess the relative contributions of climate change and human activities to terrestrial ecosystems NPP [30; 31; 32]. The first approach uses regression models (pixel-specific linear regression [33], partial least squares regression (PLSR) model [34], multiple linear regression [35], etc.) to assess the relative contribution of each factor [36]. Another approach is to compare the residuals between observed NPP and predicted NPP by modeling methods, such as land surface modeling [37]. However, quantitative assessment of the relative impacts of climate change and human activities on spatial-scale changes in NPP remains a challenge for NPP research in terrestrial ecosystems due to the lack of reasonable assessment methodologies [38]. In the face of changing climate and on their implications in forest productivity, temperature and drought have great effects on forest growth under different altitudes and phenological conditions, elevation gradient is an important indicator of ecological process [39; 40]. Overall, the interpretation of the combined effects of multiple factors on NPP, especially the interaction between these factors, has yet remained unclear [12]. The Yangtze River Delta is located in the central-eastern part of China. It is one of the most dynamic regions in the global economy and one of the most urbanized regions in China [41].