Trend and future persistence of leaf area index across transboundary river basin landscapes in Central Asia

The middle and lower reaches of the Irtysh River form a transboundary ecological corridor across the Republic of Kazakhstan and Russia and represent an environmentally sensitive region in arid Central Asia. Understanding long-term vegetation dynamics in this region is essential for evaluating ecological stability and supporting cross-border ecosystem management. However, existing studies are mostly confined to individual administrative units, breaking the eco-hydrological integrity of transboundary basins; meanwhile, most analyses rely on single annual-mean vegetation metrics, failing to reveal the differentiated variation patterns and long-term persistence of LAI across different vegetation growth states. This study used the Global Inventory Modeling and Mapping Studies Leaf Area Index 4 g (GIMMS LAI4g) dataset and Climate Research Unit (CRU) precipitation data from 1982 to 2020, to investigate the spatiotemporal dynamics of leaf area index (LAI) across 14 transboundary subregions in the middle and lower reaches of the Irtysh River Basin. Specifically, this study applied Mann-Kendall trend analysis and Theil-Sen median slope estimator to identify long-term trends, employed rescaled range analysis evaluate long-term persistence, conducted Pearson correlation analysis to quantify the relationship between LAI and precipitation, and used spatial pattern analysis to characterize regional heterogeneity. The results showed significant increases in annual mean and maximum LAI, with Sen's slopes of 0.0025/a and 0.0077/a, respectively, whereas annual minimum LAI exhibited a significant decreasing trend (–0.0011/a). Pronounced spatial heterogeneity was observed among mountainous and piedmont regions, steppe–riparian transition zones, and downstream forest–wetland landscapes. Rolling-window analysis revealed relatively stable vegetation dynamics during the early period, followed by enhanced spatial divergence and increased interannual variability after the early 2000s. All LAI indicators exhibited strong persistence, with Hurst exponents exceeding 0.7000 across the study area, indicating that the observed vegetation trajectories are likely to persist in the future. Precipitation showed significant positive correlations with annual maximum and mean LAI in 64.29% and 57.14% of the study area, respectively, whereas annual minimum LAI showed generally weak responses to precipitation variability. These findings improve understanding of vegetation dynamics and future persistence in transboundary arid river basins and provide scientific support for ecological conservation and sustainable watershed management in Central Asia.