Derivation of Energy Resources from Modelled Net Primary Productivity for Germanys Forests

Abstract

In this study we will present an approach to validate modelled Net Primary Productivity (NPP) and to estimate energy potentials for forests. Germany’s forests were chosen as area of investigation. The German Remote Sensing Data Center is operating the process model BETHY/DLR (Biosphere Energy Transfer Hydrology Model) [1]. This model is an adaption of the JSBACH (Jena Scheme of Atmosphere Biosphere Coupling in Hamburg) model [2] which computes the biosphere atmosphere exchange within the global climate model ECHAM5 model. BETHY/DLR is driven by remote sensing data derived from the sensor VEGETATION (GLC2000 and time series of the leaf area index (LAI)) while meteorological input data are derived from the European Center for Medium Range Weather Forecast (ECMWF). Furthermore information about the altitude (SRTM) and a soil map (FAO) are needed. In order to validate the modelled NPP data about the increase of above ground biomass (AGB), derived from the National Forest Inventory (NFI) of Germany, are used. The NFI contains data about the increase of AGB for the four main tree species in Germany (beech, oak, pine and spruce) on NUTS-1 level, which are given in steps of twenty years (0-20, 20-40, …). Since the NFI data is valid for the years 2000 and 2001, the validation approach was used for these years. The validation is performed by converting modelled NPP to AGB at NUTS-1 level. This is done by applying volume expansion factors. With this method high coefficients of determination (r²) of about 0.95 are found, combined with an underestimation of about 41%. The result shows that the presented method delivers highly correlated results and can be seen as suitable for validating modelled NPP with statistical derived data. In a second step theoretical energy potentials were substituted from the modelled and validated NPP results, assuming sustainable use practices of forests, meaning only the annual increase of AGB is used for energy production. This is done by using tree species and age depending heating values. Applying this, theoretical energy potentials of up to 695PJ are found.