Spatial and temporal variability of land CO₂ fluxes estimated with remote sensing and analysis data over western Eurasia

The Eurosiberian Carbonflux project was designed to address the feasibility of inferring the regional carbon balance over Europe and Siberia from a hierarchy of models and atmospheric CO2 measurements over the continent. Such atmospheric CO2 concentrations result from the combination of connective boundary layer dynamics, synoptic events, large-scale transport Of CO2, and regional surface fluxes and depend on the variability of these processes in time and space. In this paper we investigate the spatial and temporal variability of the land surface CO2 fluxes derived from the TURC model. This productivity model is driven by satellite NDVI and forced by ECMWF or REMO meteorology. We first present an analysis of recent CO2 flux measurements over temperate and boreal forests, which are used to update the TURC model. A strong linear relationship has been found between maximum hourly CO2 fluxes and the mean annual air temperature, showing that boreal biomes have a lower photosynthetic capacity than temperate ones. Then, model input consistency and simulated CO2 flux accuracy are evaluated against local measurements from two sites in Russia. Finally, the spatial and temporal patterns of the daily CO2 fluxes over Eurasia are analysed. We show that, during the growing season (spring and summer), the daily CO2 fluxes display characteristic spatial patterns of positive and negative fluxes at the synoptic scale. These patterns are found to correspond to cloudy areas (areas with low incoming radiation) and to follow the motion of cloud cover areas over the whole domain. As a consequence, we argue that covariations of surface CO2 fluxes and atmospheric transport at the synoptic scale may impact CO2 concentrations over continents and need to be investigated