Monitoring the water cycle from satellite observations is one of the major goals of the Earth
Observation (EO) community. In fact, closing the water budget has been a long-standing objective
of international programs such as the Global Energy and Water Exchange (GEWEX) project.
After many years of hard work, calibrating the satellite data, improving inversion techniques, and
facilitating the coherency of the satellite retrievals, it is admitted that the water cycle budget can
now be closed when using the best satellite datasets. However, this closure is attained at the global
scale only, but we are far from closing it at regional and seasonal scales. Closing the budget at a
global scale was a necessary condition, but this is far from being enough. The EO data are
designed to monitor the spatial and temporal distribution of the water components, not to provide
global and yearly mean numbers. In this context, this study has two main objectives:
study/improve the water budget at a regional level from EO data, and to support the HYdrological
cycle in the Mediterranean Experiment (HYMEX) initiative to better monitor the water cycle in
the Mediterranean region.
