Modeled Net Ecosystem Productivity in the Yellow River Basin: Spatiotemporal Variability and Associations with Climate Extremes Across Ecological Zones

How modeled ecosystem carbon balance varies across the contrasting hydroclimatic zones of the Yellow River Basin, and whether its relationships with climate extremes differ among these zones, remain insufficiently understood. To address this knowledge gap, this study examined the spatiotemporal variability of modeled net ecosystem productivity (NEP) and its associations with temperature- and precipitation-extreme indices across three major ecological zones of the basin. Using satellite-derived NDVI, reanalysis climate data, and extreme climate indices for 2000–2022, we estimated NEP from CASA-simulated net primary productivity and modeled heterotrophic respiration, and assessed its temporal trends and climatic associations across three ecological zones. Three principal findings were obtained: (1) Over the 23-year study period, basin-wide NEP showed a statistically significant increasing tendency (β = 2.699 g C m−2 a−1), with a well-defined spatial gradient characterized by relatively lower productivity in the northwestern areas and elevated productivity toward the southeastern regions. (2) Modeled NEP increased across all four seasons. Summer showed the largest positive trend, whereas autumn and winter remained net carbon-release seasons but became progressively less negative over the study period. (3) The statistical associations between modeled NEP and extreme climate indices varied markedly across ecological zones. Extreme-precipitation indices were generally positively associated with modeled NEP in the arid northwestern zone, whereas several extreme-temperature indices showed predominantly negative associations in the northeastern monsoon-influenced region. Collectively, these findings provide model-based evidence of spatially differentiated associations between ecosystem carbon balance and climate extremes across the YRB, supporting regional ecosystem assessment and climate-adaptation planning.