The abundance of water in all three phases makes the Earth unique in the solar system. Knowledge of the fluxes and changes of phase of water are essential for an understanding of weather, climate and, indeed, of life itself. This book provides a treatment of advances in our understanding through improvements in global models, in the representation of the processes included in the models, and in related observations. It deals with fluxes within the atmosphere, at and beneath the land and ocean surface, and the interaction between them. In order to provide authoritative and coherent coverage of an area of environmental science that is developing rapidly, the book draws upon the expertise of many of the world's leading researchers across a wide range of meteorology, hydrology and oceanography. The book will be of main interest to graduate students and researchers in these subjects, but it will also appeal to final-year undergraduate students.