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Modelling and Validating Agricultural Biomass
Potentials in Germany and Austria using BETHY/DLR
M. Tum1, M. Niklaus1, K.P. Günther1, M. Kappas2
1German Aerospace Center (DLR), German Remote
Sensing Data Center (DFD), Land Surface
Dynamics 2Department of Cartography, GIS Remote
Sensing, Institute of Geography,
Georg-August-University Goettingen, Germany
We are presenting a new approach to validate
modelled Net Primary Production (NPP). Our NPP
results are computed with the dynamic vegetation
model BETHY/DLR (Biosphere Energy Transfer
Hydrology Model). BETHY/DLR is a modification of
the JSBACH model which computes the
biosphere-atmosphere exchange within the ECHAM5
global climate model. Primarily the
photosynthetic rate of vegetation types is
computed with time steps of one hour and with a
spatial resolution of about 1km². It includes
modules for assessing the water balance and the
radiative energy transfer between atmosphere,
vegetation and soil.
The model is driven by remote sensing data sets
(land cover / land use from GLC2000 and time
series of Leaf Area Index (LAI)), derived from
SPOT-VEGETATION, meteorological parameters
provided by the European Center for Medium Range
Weather Forecast (ECMWF) and soil type
information by the Food and Agriculture
Organisation (FAO). In order to validate the
modelled NPP, crop yield estimates derived from
national statistics are used to calculate above
and below ground biomass by using conversion
factors of corn to straw and leaf to beet
relations (table 1). With this method we found
coefficients of determination of up to 0.79
(figure 2).
Statistical yield data do not represent biomass
or accumulated carbon and therefore cannot be
compared directly with the modelled yearly NPP
sum (figure 1). Simple allocation schemes are
used to calculate above and below ground biomass
(table 1). Furthermore estimations of water and
carbon contents of straw and yield are needed to
estimate the carbon content from yield data (see
formulas below).
Table 1 Corn to straw (leaf to beet) ratios and
above ground to below ground ratios, carbon and
water content for selected crops

• Figure 2 Correlations between modelled NPP
  (BETHY/DLR) and statistical yield data (Federal
  statistic bureaus) in kilo tons per NUTS-3 area.
• underestimations for Germany (4 to 28)
• overestimations for Austria (8 to 51)
• coefficients of determination - Germany 0.58 to
  0.79
• - Austria 0.74 to 0.75

• Figure 1 Accumulated yearly sums of modelled
  carbon (NPP) for agricultural areas for the years
  2000 and 2001. The spatial resolution is about
  1km x 1km. White pixel represent areas which do
  not belong to the agricultural GLC2000 classes 16
  or 18.
• Model results (in Mt carbon) 2000 Germany
  76.4, Austria 5.7
• 2001 Germany 73.2, Austria 8.0
• Maximum NPP 2000 661 t carbonkm-2 2001 547
  t carbonkm-2

yi yield stw straw H2O Water content C carbon
content agb above ground biomass bgb below
ground biomass ?stw conversion factor
yi/stw ?agb conversion factor agb/bgb