LARGE-SCALE EXPERIMENTAL AND MODELING STUDIES OF HYDROLOGICAL PROCESSES

The terrestrial hydrological cycle is a critical component of the Eart h system, playing a key role in climate processes, biogeochemical cycl es and their interactions. Better knowledge about the land/atmosphere exchanges of water is also needed to maintain human development, by im proving water management practices and providing a better understandin g of the local, regional and global consequences of human impacts on f reshwater resources. Research into global hydrology is fostered under several international projects and programs. This paper briefly overvi ews past activity and progress in the field of large-scale observation s and their associated modelling. It then previews upcoming activities , discerning a change of emphasis: increasing effort is now being give n to broadening objectives, with more attention directed at larger-sca le observations and truly interdisciplinary studies. These involve obs ervations which are geographically widely-distributed, to sample a ran ge of natural and man-made eco-climatological gradients.