Modelling the Biospheric Aspects of the Hydrological Cycle

The International Geosphere-Biosphere Program — Biological Aspects of the Hydrological Cycle (IGBP-BAHC) is concerned with the role of the biosphere in the hydrological cycle over a range of space and time scales. One crucial emphasis in this exercise involves ‘upscaling’ or aggregating the processes in the soil-vegetation-atmosphere interface from the patch scale of ecology to the mesoscale, larger regional scales and the continental scale. In time the upscaling must move from hours to decades and even longer time periods. A second emphasis involves the ‘downscaling’ of low-resolution climatic and meteorological data to high-resolution grids that are suitable for ecological and hydrological research. These two emphases are described along with prototype models for upscaling and downscaling. Other issues such as the incorporation of land surface heterogeneity in upscaling and the classification of atmospheric circulation patterns in downscaling are discussed along with other aspects related to these emphases are presented in greater detail. In particular the discussion of the downscaling component in BAHC summarizes the results of the most recent workshops (BAHC, 1993a and b).