Developing the Global Geodetic Observing System into a Monitoring System for the Global Water Cycle (IGCP 565 Project) Hans-Peter Plag 1* , Norman Miller 2 , Richard S. Gross 3 , Markus Rothacher 4 , Susanna Zerbini 5 , Chris Rizos 6 1) Nevada Bureau of Mines and Geology and Seismological Laboratory, University of Nevada, Reno, NV, USA, hpplag@unr.edu . 2) Berkeley National Laboratory and University of California, Berkeley, CA, USA. 3) Jet Propulsion Laboratory, California Inst. of Technology, Pasadena, CA, USA. 4) GeoForschungsZentrum Potsdam, Potsdam, Germany. 5) Department of Physics, Sector of Geophysics, University of Bologna, Italy. 6) School of Surveying & Spatial Information Systems, University of New South Wales, Sydney, Australia. ABSTRACT Geodetic observations of the Earth's gravity field, shape, and rotation and their changes in time (the three fundamental areas of geodesy) capture the signals of variation in the entire fluid envelope of the solid Earth, including the terrestrial water storage. Therefore, the Global Geodetic Observing System (GGOS) has the capability to monitor mass transport particularly in the global water cycle. The IGCP 565 Project aims to utilize this potential and to develop GGOS into a monitoring system for the hydrological cycle on global to regional scales. Key scientific issues addressed are: (1) Development of an integrated dynamic model for the predictions of the geodetic signals of daily to interannual surface mass changes; (2) Inversion algorithms for integrated geodetic observations for surface mass changes; (3) Assimilation of observed surface mass changes in hydrological models; and (4) Development of products relevant for regional water management. The project supports capacity building in space-geodetic data processing, modeling of the hydrological cycle, and interpretation of the observations in terms of terrestrial water storage. A focus is on products for regional water management, particularly in developing countries. Coordination of the research and capacity building is provided through a series of five annual workshops. Keywords: Monitoring of the Global Water Cycle, Global Geodetic Observing System, Earth Observation, Regional Water Management, Capacity Building 1. INTRODUCTION Water is essential to life on Earth, which is a unique, living planet due to the abundance and vigorous cycling of water throughout the global water cycle. Water is central to human welfare, progress and sustainable economic growth. Clean, fresh water is arguably the most important resource to human society, as it controls our ability to produce sufficient food to support the human population. In many areas of the world, current demands exceed the supply (as indicated by the water scarcity index, see Oki & Kanae, 2006) and water has to be transported over great distances. This situation is expected to become more severe over the next several decades (see, e.g., EEA, 1999; Lawford et al., 2004; Bernasconi et al., 2005; Oki & Kanae, 2006; United Nations, 2006). However, the water crisis is largely a crisis of governance (United Nations,