Process‐based TRIPLEX‐GHG model for simulating N2O emissions from global forests and grasslands: Model development and evaluation

The development of the new process-based TRIPLEX-GHG model derives from the Integrated Biosphere Simulator (IBIS), which couples nitrification and denitrification processes to quantify nitrous oxide (N2O) emissions from natural forests and grasslands. Sensitivity analysis indicates that the nitrification rate coefficient (COENR) is the most sensitive parameter to simulate N2O emissions. Accordingly, we calibrated this parameter using data from 29 global forest sites (across different latitudes) and grassland sites. The average nitrification rate coefficient gradually increases in the order of tropical forest to grassland to temperate forest to boreal forest, and giving means of 0.009, 0.03, 0.04, and 0.09, respectively. This study validated the mean value for each ecosystem at 52 sites globally. Calibration results both indicate the good performance of the model and its suitability in capturing seasonal variation and magnitude of N2O flux; however, it is limited in modeling N2O uptake and increments during periods of snowmelt. Additionally, validation results indicate that simulated and observed annual or seasonal N2O fluxes are highly correlated (R2=0.75; P<0.01). Consequently, our results suggest that the model is suitable in simulating N2O emissions from different forest and grassland land types under varying environmental conditions on a global scale.