Project 565 - Geodetic Monitoring of the Global Water Cycle
Water is essential to life and central to human welfare, progress and sustainable economic growth. The global hydrological cycle operates on a continuum of temporal and spatial scales. Its variability which regulates flood, drought, and disease hazards is being continuously transformed by climate change, erosion, pollution, agriculture, and civil engineering practices. Despite its fundamental role for mankind, and despite the challenges through increasingly limited availability of water for human activities, knowledge of key quantities of the hydrological cycle is still associated with large uncertainties, and urgent questions cannot be answered.
Geodetic observations relate to the Earth's gravity field, shape, and rotation and their changes in time (the three fundamental areas of geodesy). At time scales from weeks to decades, hydrological loading of the Earth's surface dominates non-secular variation in each of these areas of geodesy. Thus, geodesy naturally provides integral constraints on the water cycle at multiple spatial and temporal scales. Space-geodetic sensors capture the signals of variation in the entire fluid envelope of the solid Earth, including the terrestrial water storage. Space geodetic observations of surface mass variability are inherently strong at regional to global scales, and could be an important complement to traditional in-situ measurements of terrestrial water storage.
The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) has the capability to monitor mass transport in the Earth system and particularly the global water cycle. Crucial to this application are the gravity satellite missions that measure the temporal variability of the Earth's gravity field. The GRACE mission has demonstrated the great potential of these missions, but the continuity of the satellite missions is not secured. Moreover, the utilization of the full suite of the geodetic observations is hampered by model insufficiencies, inconsistencies, and a lack of integration of the different space-geodetic techniques. As a consequence, the dissemination of products into practical water management has not taken place.
The proposed project aims to develop GGOS into a monitoring system for the hydrological cycle on global to regional scales. The intergovernmental and international frames of the Group on Earth Observation (GEO) and GGOS, respectively, will be used to ensure sufficient satellite gravity missions, particularly with participation of emerging space agencies in Africa and Asia. Ongoing and planned research will: address the combination of space-geodetic observations, particularly GPS and GRACE-type observations, in order to exploit their individual strengths and mitigate their weaknesses; improve the geophysical models for the processing of the observations; enhance the extraction of highly accurate information on changes in terrestrial water storage, prepare the assimilation of the observations in integrated predictive models of the hydrological cycle, and focus on the interpretation of the space-geodetic observations in terms of regional groundwater and soil moisture changes.
Through cooperation with research institutions in developing countries, the project will support capacity building in the field of space-geodetic data processing, modeling of the hydrological cycle, and interpretation of the observations in terms of terrestrial water storage. Through interaction with water management authorities particularly in developing countries, the practical use of the products for regional water management will be promoted. Coordination of the research and capacity building will be provided through a series of five annual workshops, with the first one focusing on satellite gravity missions, a second and third one on data processing, technique integration, modeling and interpretation, and the last two on hydrological applications, particularly in developing countries. Expected results are an improved understanding of mass redistribution in the water cycle, in particular, changes in groundwater; better exploitation of the space-geodetic observations for hydrology; and societal benefits through an improved knowledge basis for regional water management.