Conference Agenda

Vegetation optical depth (VOD) derived from microwave satellites provides critical information on vegetation water content as well as biomass and has emerged as a valuable remote sensing metric for quantifying water stress impacts on vegetation carbon uptake. However, as ground validation of VOD remains challenging, terrestrial biosphere models (TBMs) have been developed as essential tools for comprehensive validation and broader application of VOD. By incorporating plant hydraulic modeling schemes, TBMs can simulate key vegetation water status variables (such as leaf water potential), thereby enabling the simulation of VOD. In this study, we developed a novel plant hydraulics module within the adjoint-based Nanjing University Carbon Assimilation System (NUCAS) to facilitate VOD simulation. Parameter sensitivity analysis was conducted to identify key parameters influencing VOD. Simulated VOD was validated against microwave remote sensing-derived VOD observations and biomass data. Subsequently, VOD observations were assimilated into the NUCAS integrated with the plant hydraulic module to improve model representation and to enhance understanding of ecosystem processes. Results showed that the model accurately reproduces the seasonal dynamics observed in satellite-based VOD, and the simulated VOD is strongly sensitive to plant hydraulic parameters, including saturated hydraulic conductivity and minimum leaf water potential. Moreover, the assimilation of VOD effectively constrained vegetation hydraulic processes, leading to improved model representation of ecosystem carbon and water fluxes/storage. In summary, our study provides valuable insights for model development, validation, and application related to microwave satellite-derived VOD, and opens new perspectives for advancing the understanding of carbon-water processes within terrestrial ecosystems.