The Mediterranean region features a nearly closed sea surrounded by urbanized littorals and mountains that acts as a transition zone between humid climates to the north and arid climates to the south. As a result, the region experiences many interactions and feedback between oceanic, atmospheric, and hydrological processes, as well as anthropogenic activities. Understanding these interactions, links to extreme weather events and climate change impact is essential for the environmental and socio-economic prosperity of the region encompassing southern Europe, northern Africa and the Middle East. Understanding the different processes and interactions governing the water cycle in the Mediterranean region is a key challenge for the scientific community and a major requirements to societal development. To address these major scientific challenges HyMeX (HYdrological cycle in the Mediterranean EXperiment) aims at a better understanding and quantification of the hydrological cycle and related processes in the Mediterranean, with emphasis on high-impact weather events, inter-annual to decadal variability of the Mediterranean coupled system, and associated trends in the context of global change. In this context, , the overarching objective of the WACMOS-MED project is to contribute to HYMEX scientific objectives by advancing in the exploitation of ESA and non-ESA EO datasets to enhance our understanding of the water cycle in the Mediterranean area through an integrated approach involving jointly the land, the ocean and the atmosphere components. This activity aims at answering the following questions:

• Are existing EO products suitable to characterise the different components of the water cycle over land, ocean and atmosphere over the Mediterranean area in terms of accuracy, uncertainty, resolution, observation frequency and consistency (temporal and inter-product consistency)?
• How existing products compare with models and reanalysis over the Mediterranean area?
• What are the main gaps and deficiencies of existing products and what are the required developments in order to develop a long-term consistent dataset characterising the ocean, land and atmosphere components of the water cycle dedicated to the Mediterranean area?
• What is the water budget in the Mediterranean based on satellite-based products and how that compare to modelling and reanalysis results?
• How is the water cycle dynamics in the Mediterranean as described by satellite information and how that compare to modelling and reanalysis data?
• Can emerging techniques exploiting the water balance equation at basin scales be extended to a regional case (with focus on the Mediterranean area) to develop a coherent enhanced EO-based dataset that ensure water budget closure coherency over the Mediterranean?
• What is the added value of EO datasets to address some of the main open questions in science over the Mediterranean area (e.g., extreme events).
• What are the future perspectives and science challenges where EO technology may contribute to address the main open questions in Water cycle research and applications in the Mediterranean area