The ECMWF land surface scheme extended with a photosynthesis and LAI module tested for a coniferous site

The stomatal conductance scheme and vegetation evolution module that are employed in
the ISBA­A­gs soil­vegetation­atmosphere transfer model, are implemented in the ECMWF
land surface scheme TESSEL. The new scheme, called C­TESSEL, is able to simulate carbon
fluxes and to calculate LAI dynamically. C­TESSEL is tested for a coniferous forest site in
the Netherlands. Simulated carbon and latent heat fluxes are validated against micrometeo­
rological observations. The latent heat flux is simulated with acceptable accuracy, both with
respect to observations and to simulations by the unmodified TESSEL model. However, it
is shown that the quality of the simulated carbon fluxes is not su#cient to allow the present
configuration of C­TESSEL to be used in a data assimilation system. A general sensitivity
analysis on three vegetation type specific parameters indicates that the simulated latent heat
flux is highly sensitive to the presence of vegetation via the leaf nitrogen content and ­ when
vegetation is not limited ­ also to the soil moisture conditions. The latent heat flux turns
out to be insensitive to the parameter chosen to represent the influence of the photosynthetic
activity (mesophyll conductance under unstressed soil moisture conditions) due to compen­
sating e#ects of associated parameters concerning the e#ect of humidity deficit on stomatal
conductance. The sensitivity analysis also shows that for the coniferous forest site, C­TESSEL
is not able to simulate both the right magnitude of the latent heat flux and the day­to­day
variability with a given set of parameter values.