By now several flux measurement sites have decadal+ records of terrestrial carbon dioxide, water vapour and energy fluxes. Both empirical analysis and simulation studies with process-oriented models have problems in explaining the observed inter-annual variability. This session is intended to focus on studies bringing together field observations and experiments with statistical and process-based modelling approaches. Discussion will center around our current knowledge of the causes of the observed inter-annual variability and aims to indicate areas and avenues for improving models. Contributions which combine both aspects are particularly encouraged.