Estimation of carbon mass fluxes over Europe using the C-Fix model and Euroflux data

One of the aims of the EU funded project Long-term regional effects of climate change on European forests: impact assessment and consequences for carbon budgets (LTEEF-II, ENV4-CT97-0577) is to quantify the fluxes of carbon and water between vegetation (forests) and atmosphere and to assess the carbon balance of forests in Europe. This paper presents the results of the application of the C-Fix model within the frame of part of the objectives of the LTEEF-II project, as defined for the European continental scale. A description of the C-Fix model is presented in the first part of this paper. C-Fix is a Monteith type parametric model driven by temperature, radiation and fraction of Absorbed Photosynthetically Active Radiation (WAR), the last variable derived by processing NOAA/AVHRR data of 1997 acquired over Europe as well as VEGETATION (VGT) data for the same region for the period 1998-1999. In a second part of the paper, the main results obtained are described, e.g. net ecosystem fluxes for forest, calculated locally for the Euroflux CO2 measurement sites as well as for the whole continent. The model simulations were evaluated with eddy covariance measurements of NEP performed during 1997 at the Euroflux sites. Moreover, a comparison between NEP determined with NOAA/AVHRR data, opposed to NEP simulations based on VGT data is performed. A difference up to 20% is obtained between both data sets. Finally A C-Fix estimate of total European vegetation NEP obtained with NOAA/AVHRR data for 1997 is 2.70 +/- 32% Pg C, (P = 10(15) g, % is 95% confidence limit). This estimate decreases to 2.15 +/- 43% Pg C when VGT data for the period April 1998-March 1999 are used. The total forest NEP for Europe, however, is estimated at 0.735 Pg C for 1997. Along a North-South transect at 13degrees east, through Europe a clear increase in NEP and the other basic carbon mass fluxes GPP and NPP is modelled from northern to southern latitudes. Moreover, along this transect the values simulated with C-Fix for NEP corresponds well with the eddy covariance NEP estimates for the Euroflux sites. (C) 2002 Published by Elsevier Science Inc.