Recent advances in Earth observation (EO) satellites have made possible the global observation of several key variables governing the global water cycle. In the coming years an increasing number of EO missions will provide an unprecedented capacity to observe the Earth surface, its interior and the atmosphere, opening a new era in the use of EO for water cycle science and hydrology. The recent successful launches of SMOS and CryoSat by the European Space Agency will open the door to new scientific results and advances in the understanding and characterisation of the water cycle. The full exploitation of this capacity requires coordinated international efforts to develop robust geo-information products that may exploit the synergies offered by the increasing number of water relevant EO missions. In particular, the specific objectives of this session are:

(1) To assess recent progress and uncertainties in the full range of water cycle observations: precipitation, clouds, evaporation, water vapour, soil moisture, run-off, surface water levels, surface water and groundwater measurements as well as surface heat fluxes and the Earth radiation budget;
(2) To identify the main needs and uncertainties in modelling and data assimilation to integrate those EO-derived products to improve our ability to quantify future changes in water cycle variables;
(3) To highlight the challenges and to advocate the opportunities in water cycle science in order to reduce uncertainties in water related climate change impact assessments and adaptation strategies in water resources;