An approach for simulating the phenology of savanna ecosystems in the Laboratoire de Meteorologie Dynamique general circulation model

Plant phenology, defined here as the seasonal variations of green and dead biomasses in response to climatic conditions, is an important parameter for the modeling of biophysical exchanges between vegetation and atmosphere. However, the adequate simulation of plant phenology, particularly in tropical regions, is still lacking in current general circulation models (GCMs). This paper proposes a modeling approach to simulate the phenology of savanna grasses in the Laboratoire de Meteorologie Dynamique (LMD) GCM. A plant production and phenology model (PPP) is developed to simulate the temporal variations of green and dead aboveground biomasses and leaf area index (LAI) using climate variables computed by the LMD GCM. In addition, the PPP model simulates the occurrence of savanna fire. Predictions are compared to harvest measurements of grasses from two different regions of savanna: the region of Lamto, West Africa, and the region of Victoria River district, northern Australia. Results show that the PPP model generates reasonably realistic plant seasonal variations in these two regions, despite the existing biases in the simulated climate variables. Both the frequency and timing of fire occurrence are, moreover, realistically simulated. This model, linked to the GCM, could be used as a tool to investigate the effects of fire disturbances and short-term (i.e., seasonal and interannual) savanna vegetation feedbacks on climate.