Carbon sequestration simulation study based on the Soil and Water Analysis Tool model in the Yiluo River Basin

In terrestrial ecosystems, water and carbon cycles are closely coupled through processes such as photosynthesis, transpiration, and carbon allocation. Although advancements have been made in water-carbon coupling, existing studies predominantly focus on measurement methods and ecosystem model analysis, with insufficient attention paid to the linkages between hydrological processes and vegetation dynamics. This study employed the Yiluo River Basin as a case study, utilizing the Soil and Water Analysis Tool model to simulate the basin's hydrological cycle. By deconstructing and reconstructing the original hydrological response unit structure, this modified model was used to simulate actual evapotranspiration and potential evapotranspiration for each hydrological response unit. By applying the light use efficiency model and integrating evapotranspiration and potential evapotranspiration data, researchers determined the spatiotemporal distribution characteristics of carbon sequestration-namely, gross primary productivity (GPP) and net primary productivity (NPP)-thereby enriching research on water-carbon linkages. Key findings were as follows: (a) Annual average GPP and NPP showed a significant upward trend, with NPP values slightly lower than GPP. (b) The annual average values in the upstream areas were notably higher than those in the downstream areas, closely related to vegetation types and evapotranspiration distribution. (c) Summer acted as the primary season for GPP and NPP accumulation, typically exhibiting high evapotranspiration rates and strong carbon sequestration. Over time, spring cumulative contributions of GPP and NPP have gradually increased, as driven by climate change and vegetation restoration, thus narrowing the seasonal gap relative to summer.