Challenges for Observing and Modeling the Global Water Cycle

This chapter outlines issues related to observing and garnering information about the global water cycle. The challenges in developing an adequate climate observing system, especially for the hydrological cycle-related variables are also outlined. The chapter then provides a brief summary of some recent evaluations of the state of knowledge about the global aspects of the water cycle, and outlines the Global Energy and Water Exchanges (GEWEX) programmatic plans to address these issues over the next decade. The successful implementation of World Climate Research Programme (WCRP) grand challenges and associated science questions described in the chapter depend significantly on GEWEX imperatives: observations and data sets, their analysis, process studies, model development and exploitation, applications, technology transfer to operationalize results, and research capacity development and training of the next generation of scientists.