Strictly speaking, the water (or hydrologic) cycle is a global phenomenon. To observe, analyze, understand and predict its structure and variations demands a coordinated and integrated effort of global observations and global prediction systems. The National Aeronautics and Space Administration (NASA) has the unique capability of space-based experimental and research measurements that observe the Earth's system to advance scientific understanding as well as modeling activities that exploit these space-based observations to improve weather and climate predictions. Currently, NASA's Global Water and Energy Cycle and Terrestrial Hydrology (formally known as the Land Surface Hydrology) Programs are the key funding sources which support water-cycle research. These programs not only fund individual scientists, but also support large-scale field missions (for example the Cold Land Processes Experiment, CLPX, and the Soil Moisture Experiment, SMEx) which are critical for calibration/validation of space instruments and retrievals as well as gaining fundamental understanding of local- and regional-scale processes which comprise the global system.

Recently, many scientific interagency panels and the governmental offices of climate change research (i.e. the U.S. Global Change Research Program, USGCRP, and the Climate Change Research Initiative, CCRI) have emphasized the need for focused, integrated and prioritized research so that the necessary advances in water-cycle science and predictions are realized in the coming decades. A new initiative for NASA Water and Energy cycle Research (WatER) is presented. Following NASA's unique vocations, WatER will not only serve and pursue NASA's overall Earth Science Enterprise research goals, but also aim to make significant strides in the understanding and prediction of the global water cycle which will foster more confident projections of the hydrologic consequences of both natural and human-induced climate change. The WatER initiative sets forth with priorities for science/research support to advance three key observations of the water cycle - precipitation, evaporation, and the land state - whose scientific end-returns should not only advance understanding and predictions of the water cycle but also scientifically benefit other critical cross-cutting themes (such as the carbon cycle). Moreover, coordinated diagnostic studies as well as modeling and assimilation activities which exploit these advanced global observations are formalized to not only harvest NASA's activities but also foster mutual and synergistic benefit with the scientific community.