| Abstract |
Continental waters have a crucial impact on terrestrial life and human needs, and play a major role in climate variability. Without taking into account the ice caps, fresh continental waters are stored in various reservoirs: the snow pack, underground reservoirs, the root zone (first few meters of the soil) and vegetation, and as surface waters (rivers, lakes, man-made reservoirs, wetlands and inundated areas). Water on Earth is continuously recycled through precipitation, evapotranspiration, runoff, and vertical and horizontal diffusion and transfer in soils. An improved description of the global water cycle, especially the yet poorly known continental branch, is of major importance for inventory and eventually better control of water resources available for human consumption and activities (agriculture, urbanisation, hydroelectric energy resources), as well as for climate prediction.
Remote sensing techniques can now be used to monitor water balance of large river basinson time scales ranging from weeks to months: among these, the most promising are satellite altimetry on surface waters (rivers and their tributaries, wetlands and floodplains) providing water levels and space gravity missions providing estimates of spatio-temporal variations of terrestrial water storage in soils (soil wetness and groundwater) and in surface water reservoirs. To be used in conjunction with in situ observations and hydrological modeling, these observations from space have the potential to significantly improve our understanding of hydrological processes affecting large river basins in response to climate variability.
A first Workshop of this kind was held in Toulouse, France, in September 2003. The summary and recommendations, published in AGU's EOS, insisted on the organisation of a sequel meeting.
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