Analysis of the spatiotemporal dynamics of natural grassland productivity and its influencing factors in the Ili River Basin of Xinjiang over the past 23 years

Objectives Grassland net primary productivity (NPP) in the Ili River Basin Grasslands, as Earth's largest terrestrial ecosystem, are crucial for global carbon cycling and ecological stability. Clarifying the spatiotemporal patterns and driving factors of grassland NPP is key to optimizing conservation strategies and enhancing productivity. Methods Using MODIS data (2000–2022) and the CASA model, this study estimated grassland NPP in the Ili River Basin, and explored its dynamic characteristics and responses to climate and human activities through trend analysis, correlation analysis, and the Hurst index. Results (1) NPP increased annually by 0.14% from 2000 to 2020, but decreased by 15.4% from 2020 to 2022, with an overall 12.95% decline over 23 years; extreme climates in 2008, 2014, and 2021 caused NPP to drop by 27.24%, 28.01%, and 21.31%, respectively, compared to the previous years. (2) High-NPP areas were concentrated in eastern mountainous regions (Nileke, Zhaosu, Tekes, etc.), while low-NPP areas were distributed in central urban zones and high-altitude regions, showing an “east-high-west-low” pattern. (3) Temperature was the main climatic driver (affecting 91,253 km²); human activities led to NPP decline in 55.94% of the area (far exceeding the 2.81% where NPP increased). (4) The Hurst index projected that 79.5% of the area would shift from decline to increase, 8% would continue to decline, and 9.81% would reverse from increase to decline. Conclusions NPP showed a downward trend from 2000 to 2022 but is expected to rise significantly in the future, providing references for conservation efforts.