Divergent responses of vegetation phenology and productivity to climate change in typical river basins across Northern and Southern China

Abstract The Yangtze River Basin (YZRB) and Yellow River Basin (YRB) are the largest river basins in China, representing typical regions in southern and northern China. Understanding the impacts of climate and phenology on net primary productivity (NPP) is essential for regional ecological protection, management and carbon neutrality. Based on remote sensing and climate data, this study quantified the temporal trends and spatial variations in vegetation phenology and NPP in the two typical regions. Pearson correlation and structural equation modeling were employed to examine the mechanisms through which climate and phenology influence NPP. The results reveal distinct NPP accumulation mechanisms in the YZRB and YRB. In the YZRB, the growing season significantly lengthened (0.60 days yr–1, P < 0.05), resulting in an annual NPP increase of 3.19 g C m–2 yr–1, primarily driven by spring NPP (52% contribution), with direct effects of temperature (β = 0.71, P < 0.001) and radiation (β = 0.63, P < 0.001) on NPP. In contrast, the YRB exhibited relatively larger NPP growth (3.54 g C m–2 yr–1), with roughly equal seasonal contributions. Precipitation regulated NPP both directly and indirectly through mediating phenology (indirect β = 0.27, P < 0.05). These findings emphasize the complexity of the effects of climate and phenology on NPP, underscoring the necessity for region-specific management strategies to optimize productivity under climate change.