Inter-annual variability of carbon and water fluxes in Amazonian forest Cerrado and pasture sites, as simulated by terrestrial biosphere models

This study analyzes the inter-annual variability (IAV) of simulations of 21 different land surface modelformulations, driven by meteorological conditions measured at 8 flux towers, located in rain forest, forest-savanna ecotone and pasture sites in Amazonia, and one in savanna site in Southeastern Brazil. Annualtotals of net ecosystem exchange (NEE) of carbon and evapotranspiration (ET), measured and simulatedby each model for each site-year, were compared in terms of year-to-year variability and possible rela-tion to climate drivers. Results have shown that most of models simulations for annual totals of NEEand ET, and IAV of these fluxes, are frequently different from measurements. The average of the modelsimulations of annual fluxes tend to respond to climatic drivers similarly to the observations, but withnoticeable discrepancies. Annual measurements of NEE are negatively correlated to annual rainfall inthe forest sites group. Although the ensemble of all models yields a similar result, only three model formulations reproduce a significant negative correlation of simulated NEE with rainfall. For the IAV of ET,tower measurements are controlled by annual variations of radiation and this feature is captured by theensemble of the models, both at individual sites and when all forest sites are grouped. However, simulatedET values are also significantly correlated to the amount of precipitation in many models and in the modelensemble, while there is no significant correlation in the observations. In general, the surface models areable to reproduce the responses of fluxes to climatic drivers, but improvements are still needed to bettercapture their inter-annual variability.