CO 2 fluxes and transpiration

Abstract

Plants play a key controlling role within the hydrological cycle. For analysing global change impacts on water resources in the Upper Danube basin, coupled and process-based modelling of vegetation water and carbon fl uxes is needed. The model component Biological is part of the simulation system DANUBIA and calculates the processes of carbon assimilation and transpiration for various vegetation categories (e.g. grassland, winter wheat, sugar beet and maize). To best depict the complex interplay of water, carbon and nitrogen fl uxes in agroecosystems, decisions on crop management are included in the modelling. Additionally, meteorological and pedological model input data are provided by other dynamically coupled DANUBIA model components. Modelling of photosynthesis and transpiration takes into account not only the predicted increases in air temperature and atmospheric CO 2 concentration but also the availability of water and nitrogen. Maps of transpiration totals for one hydrological year are presented for several agricultural land uses in the Upper Danube basin. Local conditions, characteristics of the different vegetation categories and differences in management are shown. In this way, spatial and temporal changes in plant water demand and supply under global change conditions and altered cultivation practices are assessed at the regional scale.