Technical Note: An efficient method for accelerating the spin-up process for process-based biogeochemistry models

Authors: Qu Y., Maksyutov S., Zhuang Q.
Journal: Biogeosciences, 15, 3967-3973
DOI: 10.5194/bg-15-3967-2018
Abstract: To better understand the role of terrestrial ecosystems in the global carbon cycle and their feedbacks to the global climate system, process-based biogeochemistry models need to be improved with respect to model parameterization and model structure. To achieve these improvements, the spin-up time for those differential equation-based models needs to be shortened. Here, an algorithm for a fast spin-up was developed by finding the exact solution of a linearized system representing the cyclo-stationary state of a model and implemented in a biogeochemistry model, the Terrestrial Ecosystem Model (TEM). With the new spin-up algorithm, we showed that the model reached a steady state in less than 10 years of computing time, while the original method requires more than 200 years on average of model run. For the test sites with five different plant functional types, the new method saves over 90% of the original spin-up time in site-level simulations. In North American simulations, average spin-up time savings for all grid cells is 85% for either the daily or monthly version of TEM. The developed spin-up method shall be used for future quantification of carbon dynamics at fine spatial and temporal scales.