Modelling and validation of agricultural and forest biomass potentials for Germany and Austria

Abstract

The Biosphere Energy Transfer Hydrology Model (BETHY/DLR), a process model that estimates the net primary productivity of agricultural and forested areas was used to assess biomass potentials for Germany and Austria. The model is driven by remote sensing data and meteorological data. Remotely sensed datasets including a time series of the leaf area index, which describes vegetation condition, and a land cover classification, which provides information about land use, are needed. Leaf area indices and land cover data derived from the sensor VEGETATION are used. Both datasets have spatial resolutions of about 1km x 1km and are freely available for the area of investigation. The meteorological input parameters are air temperature (at 2m height), precipitation, cloud cover, wind speed (at 10m height) and soil water content (inthe four uppermost soil layers); these are obtained from the European Centre for Medium-Range Weather Forecasts, with a spatial resolution of about 0.25° x 0.25° and a temporal resolution up to four times daily. The output of the model, the gross primary productivity, is calculated at daily resolution. By subtracting the cumulative plant maintenance and growth respiration, the net primary productivity is then determined. In order to validate the modelled net primary productivity, crop yield estimates and mean above ground biomass increases derived from the national statistics of Germany and Austria are used. After estimating above-ground biomass using plant-specific above- to below-ground ratios, conversion factors (corn-to-straw and leaf-to-beet relations) are applied to estimate total biomass. Finally the carbon content of dry matter is estimated. To correlate model results with these statistical data, the modelled data are aggregated to net primary productivity per administrative district. The results show that a process model using remote sensing data as input can deliver reliable estimates of agricultural and forest biomass potential which are highly correlated with statistically derived estimates of actual biomass produced. In addition, theoretical energy potentials calculated from the modelled and validated NPP are examined, assuming sustainable agricultural and forest management and using species-specific heating values. Such estimated sustainable biomass energy potentials play an important role in the sustainable energy debate. In order to improve the model BETHY/DLR a multi-layered soil water budget model was developed and applied. It uses van Genuchten parameters which were estimated for 128 globally available FAO soil types.