Evaluating the impact of urban expansion on ecosystem carbon based on a long time series 30 m resolution NPP dataset

• Urban expansion reduced vegetation NPP by 13.77 % in CZT from 2000 to 2020. • Direct LULC changes contributed 54.62 % to NPP loss in CZT. • Heat island effect negatively impacted vegetation NPP in CZT. Urban areas significantly influence the natural environment and play a critical role in the global carbon cycle. Quantifying the impact of urban expansion on carbon stocks is essential for assessing vegetation dynamics and regional carbon balance. This study analyzes the spatiotemporal evolution of vegetation net primary productivity (NPP) in the Chang-Zhu-Tan (CZT) urban agglomeration from 2000 to 2020 using high-resolution (30 m) Landsat NDVI, land use/land cover (LULC), and meteorological data within the CASA model. Key findings reveal that the annual mean vegetation NPP ranged between 246 and 356 g C/m 2 a −1 , with higher values in peripheral areas and lower values in urban centers. Approximately 20.01 % of the region experienced significant decreases in NPP, while only 10.11 % showed increases. Urban expansion was responsible for 13.77 % of the total NPP loss relative to the base year (2000), with pronounced reductions in eastern Changsha and urban confluences. Furthermore, direct drivers (e.g., LULC changes) contributed 54.62 % to NPP loss, while indirect factors (e.g., climate change) accounted for 45.38 %. These results underscore the dual influence of direct and indirect anthropogenic factors on carbon dynamics in rapidly urbanizing regions.