# Climate Warming Dominates Vegetation Productivity in the Hanjiang River Basin, China
Although vegetation in most regions around the world is experiencing an upward trend, research has indicated that, against the backdrop of rising temperatures, water availability has become a significant limiting factor for vegetation growth [5; 28]. Additionally, numerous studies have suggested that vegetation greening can influence regional water resources [36; 37; 38]. The Hanjiang River Basin (HJRB), located in central China, serves as the core water source for the Danjiangkou Reservoir, which is a crucial component of the South-to-North Water Diversion Project, the largest water diversion project in the world. Thanks to global warming and ecological engineering, the HJRB has undergone significant greening over the past few decades [39; 40; 41]. Research on the vegetation in the HJRB has indicated that precipitation and temperature are the primary climatic factors affecting NDVI changes. However, other climate factors such as wind speed, sunshine duration, and potential evapotranspiration, which directly or indirectly influence regional water and thermal conditions, and consequently impact vegetation growth and distribution, have been overlooked [35]. Recent studies have pointed out that vegetation greening has affected the availability of water resources in the HJRB [38]. Given that GPP influences water resources supply, water cycling, and water source conservation [15], it is imperative to investigate the mechanisms behind changes in vegetation productivity exacerbated by climate change. Moreover, due to the influence of monsoon climate, there are significant differences in precipitation, temperature, and various climate indicators between different seasons. Therefore, to gain an in-depth understanding of the impact of climate change on ecosystems, it is crucial to study the seasonal variations in vegetation and how vegetation productivity responds to these seasonal climate changes [42; 43; 44; 45]. This provides essential references for devising climate change adaptation strategies and ecological conservation. Numerous studies have delved into the relationship between vegetation and its influencing factors [7; 29; 46; 47], with several specifically addressing vegetation dynamics in the HJRB [39; 40; 41]. However, research focusing on the seasonal characteristics of vegetation dynamics while considering multiple climate factors and drought conditions remains relatively scarce. We selected the HJRB as our study area due to its unique water conservation function. Moreover, the pronounced differences between the upstream and downstream regions of the HJRB, characterized by diverse vegetation and vertical zones, ensure the representativeness of our study and offer insights for other similar water conservation areas. Thus, this study analyzes the spatiotemporal characteristics and response mechanisms of GPP in the HJRB from 2000 to 2020. The main objectives of this study are as follows: (1) to evaluate the seasonal vegetation productivity in the HJRB; (2) to explore the response mechanisms of GPP to climate factors; (3) to quantify the contributions of climate change to GPP variations in the HJRB. This research reveals the trends in GPP changes at the regional level on both interannual and seasonal scales, along with the response mechanisms to climate change. It holds significant importance for preserving the ecological environment of the HJRB and other similar areas.