## 1 Introduction  
According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [1], the global climate has warmed significantly since the industrial revolution, and global precipitation will increase but with significant regional and seasonal variations. Global air temperatures increased by at least 0.2 \({}^{\circ}\)C per decade over the past 30 years [2]. Models and observation results show that climate change significantly affects vegetation dynamics, ecosystem productivities, and water resource distributions [3, 4]. Drylands cover about 41% of Earth's land surface and support over 38% of the population [3, 4]. Dryland ecosystems are considered fragile and sensitive to climate change [4]. Aridity increases attributed to climate change would lead to a serious decline in ecological security. Inaddition, there are negative environmental consequences such as soil moisture limitation and interruption of biogeochemical cycles [5]. These changes are inconsistent with the observed greening trend on many drylands [6]. Xinjiang is a large inland province in northwest China and has large arid and semi-arid areas in inland Asia. In recent years, climate warming and precipitation reduction in Xinjiang in northern China had large impacts on the ecosystem [7; 8]. Climate warming could accelerate evapotranspiration and enhance soil moisture loss [9]. The reduced precipitation is expected to affect ecosystem function and stability [10]. Climate change appears to be detrimental to the growth of vegetation in Xinjiang. However, the vegetation was increasing in Xinjiang from 1989 to 2011 [11]. Research on how terrestrial ecosystems respond to climate variation has gained attention from scholars [9; 12; 13; 14]. Land cover and land use changes (e.g., farming and grazing), as well as society changes (e.g., rising population pressure), also have significant impacts on ecosystems [15]. It is important to improve our understanding of the roles of both climate change and human activities in affecting ecosystems in Xinjiang. Vegetation is an essential component of terrestrial ecosystems as it affects water, carbon, and energy exchanges between terrestrial ecosystems and the atmosphere [16]. As a result, the vegetation response to climate variation has been employed as a general indicator to assess the terrestrial ecosystem conditions. Many satellite-based studies used the normalized difference vegetation index (NDVI) derived from remote sensing data to analyze the spatiotemporal changes in vegetation cover [9; 13; 14]. Using NDVI is suitable for exuberant vegetation, and soil background could influence the NDVI [17]. Considering the low vegetation cover in Xinjiang, leaf area index (LAI) is used to indicate the vegetation change. LAI is defined as total plant leaf area per unit of land area [18; 19], which is an important structural parameter in terrestrial ecosystems and is directly related to the growth conditions of vegetation [17; 20]. Terrestrial ecosystems have massive exchanges with the environment for energy and materials such as water and carbon [21; 22; 23]. Changes in vegetation are bound to affect the carbon and water cycle process on the land surface [16]. Gross primary production (GPP) is the total carbon sequestration, which is an important component of carbon cycling, and it reflects the ability of vegetation to absorb carbon from the atmosphere. Terrestrial evapotranspiration (ET) is a crucial component in the hydrological cycle and energy balance, and it reflects the ability of a vegetated land surface to release water into the atmosphere. Exploring the changes and driving mechanisms of ecosystem indicators has become a focus of global change and is essential for evaluating the evolution of terrestrial ecosystems. Many studies have investigated the relationship between vegetation dynamics and climate factors to explore the underlying mechanisms for ecosystem indicator change [9; 16; 24].