The goal of the first edition ofPhysical Hydrologywas to provide a comprehensive text for upper-level undergraduates and graduate students that treats hydrology as a distinct geoscience. It attempted to develop an understanding of the conceptual basis of hydrology and an introduction to the quantitative relations that implement that understanding in answering scientific and water-resources-management questions. The text seemed to fulfill a need, and I have been pleased with its reception by my colleagues and students. My primary goals in revisingPhysical Hydrologyhave been to incorporate significant advances in the rapidly developing field of hydrologic science, to provide a more explicit connection of that science to hydrologic modeling, and to make more complete and useful the treatment of the relation between scientific hydrology and water-resources management. The major changes that have resulted are the following: Chapter 2 (Basic Hydrologic Concepts) now concludes with an introduction to hydrologic modeling, including discussions of model use, modeling terminology, and the process of model development. It also introduces the BROOK90 model, a physically based, lumped-parameter model that can be readily accessed on the World-Wide Web for student use. Discussions of the ways in which BROOK90 incorporates the physical relations discussed in the text are included as boxes in many of the subsequent chapters. Chapter 3 (Global Climate, Hydrologic Cycle, Soils, and Vegetation) now includes a tabulation of documented trends in global change of climatic and hydrologic quantities. In Chapter 4 (Precipitation), I have added a more extensive discussion of precipitation recycling and a new section on methods for handling missing data--an almost universal problem in hydrologic analysis. Also, the discussion of methods for estimating areal precipitation has been streamlined somewhat (one of the few places in which I was able to cut!). In Chapter 5 (Snow and Snowmelt), I have updated the discussion of ways of estimating energy-balance components and added a discussion of hybrid snowmelt models that combine energy-balance and temperature-index approaches. Chapter 6 (Water in Soils) now introduces the concepts of soil-moisture diffusivity and sorptivity, adds a discussion of equilibrium soil-moisture profiles, and expands the discussion of moisture redistribution. Chapter 7 (Evapotranspiration) now contains a brief discussion of soil evaporation as well as updates of the treatments of lake evaporation and energy-budget estimation. In Chapter 8 (Ground Water), the discussion of ground--water-surface-water relations has been expanded to include hyporheic flow and the Dupuit approximation for unconfined aquifers draining to streams. Chapter 9 (Stream Response to Water Input) has been reorganized so that the discussion of the mechanisms of stream response to water-input events now precedes the sections on rainfall-runoff modeling. The treatments of both mechanisms and modeling have been substantially revised and updated, and much of the detailed discussion of open-channel flow has been moved to Appendix B. Chapter 10 (Hydrology and Water Resources) has been entirely rewritten and expanded. It now includes a more complete and modern treatment of water-resource management goals and processes; a more detailed discussion of water supply and demand, including the concept of "safe yield" in various ground-water and surface-water settings and an expanded discussion of the estimation and application of flow-duration curves; a more complete discussion of water-quality issues; an expanded section on floods, including flood-frequency analysis; a completely new section on drought and low-flow analysis; and a concluding section on current and projected United States and global water use. Appendix A (Hydrologic Quantities) has been reorgDingman, S. Lawrence is the author of 'Physical Hydrology', published 2001 under ISBN 9780130996954 and ISBN 0130996955.