This book presents a state-of-the-art scientific overview of the influence of terrestrial vegetation and soils within the Earth system. It deals especially with interactions between the terrestrial biosphere and the atmosphere via the hydrological cycle and their interlinkage with anthropogenic activities. Measurements gathered in integrated field experiments in the Sahel, the Amazon, North America and South-east Asia confirm the importance of these interactions, but a substantial data consolidation effort still needs to be undertaken. Observations are complemented by modelling studies, including regional models that simulate flows and transport in river catchments, coupled land-cover and regional climate systems, and Earth-system and global circulation models. Water, nutrient and sediment fluxes in river basins are also discussed and are shown to be highly impacted and regulated by humans through land use, pollution and river engineering. Finally, the book discusses environmental vulnerability and methodologies for assessing the risks associated with regional and global climatic and environmental variability and change. The editors emphasise that the results reported in this book are based on the research work of many individual scientists and teams around the world associated with the objectives of the IGBP-BAHC and WCRP-GEWEX international research programmes.