An efficient approach to accelerate carbon–nitrogen spin-up in the DayCent model

Most terrestrial ecosystem models require carbon (C) and nitrogen (N) pools to reach equilibrium before predicting ecosystem feedbacks related to changes in land management or climate. This equilibrium is typically achieved through a spin-up simulation, which involves repeatedly running the model with a specific set of environmental conditions. The required model simulation period for these runs often exceeds the turnover time of the slowest pool (10 3 –10 4 years), making the process time-consuming, particularly for regional and global applications. We propose the Passive Pool Acceleration Spin-Up (PPASU) method to accelerate this process in the DayCent-UV model. PPASU allows the fast-turnover pools to reach equilibrium using the standard spin-up procedure, then estimates the steady-state values of the passive (i.e. slowest turnover) pool using a mass balance approach. PPASU was implemented at two herbaceous and two forested sites, producing C and N pool estimates below 6% error compared to long-term standard spin-up results, while achieving more than 86% computational efficiency.