title: How sensitive are estimates of carbon fixation in agricultural models to input data?
abstract: BACKGROUND
  Process based vegetation models are central to understand the hydrological and carbon cycle. To achieve useful results at regional to global scales, such models require various input data from a wide range of earth observations. Since the geographical extent of these datasets varies from local to global scale, data quality and validity is of major interest when they are chosen for use. It is important to assess the effect of different input datasets in terms of quality to model outputs. In this article, we reflect on both: the uncertainty in input data and the reliability of model results. For our case study analysis we selected the Marchfeld region in Austria. We used independent meteorological datasets from the Central Institute for Meteorology and Geodynamics and the European Centre for Medium-Range Weather Forecasts (ECMWF). Land cover / land use information was taken from the GLC2000 and the CORINE 2000 products.
  
  
  RESULTS
  For our case study analysis we selected two different process based models: the Environmental Policy Integrated Climate (EPIC) and the Biosphere Energy Transfer Hydrology (BETHY/DLR) model. Both process models show a congruent pattern to changes in input data. The annual variability of NPP reaches 36% for BETHY/DLR and 39% for EPIC when changing major input datasets. However, EPIC is less sensitive to meteorological input data than BETHY/DLR. The ECMWF maximum temperatures show a systematic pattern. Temperatures above 20°C are overestimated, whereas temperatures below 20°C are underestimated, resulting in an overall underestimation of NPP in both models. Besides, BETHY/DLR is sensitive to the choice and accuracy of the land cover product.
  
  
  CONCLUSIONS
  This study shows that the impact of input data uncertainty on modelling results need to be assessed: whenever the models are applied under new conditions, local data should be used for both input and result comparison.
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Deutsches Fernerkundungsdatenzentrum (DFD), Oberpfaffenhofen, D-82234 Wessling, Germany. markus.tum@dlr.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Tum
authors.forename: Franziska
authors.initials: F
authors.lastname: Strauss
authors.forename: Ian
authors.initials: I
authors.lastname: McCallum
authors.forename: Kurt
authors.initials: K
authors.lastname: Günther
authors.forename: Erwin
authors.initials: E
authors.lastname: Schmid