In recent years, international organizations and rich scientific activity have pointed out water as a strategic issue for the economic development of the Mediterranean region. This region is characterized by a severe and continuous decline in surface and groundwater resources in terms of both quantity and quality, combined with an increase in demand, among which 70–80 % relates to agricultural activities. This situation is exacerbated on the southern shore of the Mediterranean, where the specificity of climate (aridity and frequent droughts) combined with changes induced by human activities increase the risk of water shortage. In order to answer these societal challenges, it is necessary to implement systemic approaches of the eco-hydrological functioning of agro-systems in connection with physical reservoirs (storage and renewal capacities) and actors (operators and managers). The targeted spatial scales are the scales of the decision-making processes ranging from the plot for irrigation scheduling to the intermediate scale of the catchment for resource planning in the whole Mediterranean region. Long-term observations are essential for both resource management and eco-hydrological model development and calibration over a wide range of climate conditions including extremes that are likely to become more frequent in the future. Current water resource observation systems were thought to provide a good picture of available supply at the catchment outflow locations, but are affected by a loss of data quality, a decrease in the number of gauging stations, and the lack of available data since the 1980s. In particular, upstream processes such as snowpack dynamics and subsurface flows that contribute to groundwater recharge and downstream usage are poorly monitored, and the sediment exports from the continent to the sea are poorly known, giving no clue to understanding how arable lands are removed and transported out of the cultivated areas. These topics have received the attention of the international community, within which the SICMED program (continental surface and interface in the Mediterranean) (CNRS/INSU, MISTRALS program) has supported many research actions for 10 years, some results of which are expected to be presented in this issue.

This special issue welcomes studies dedicated to the water cycle and the water resources in the semi-arid Mediterranean areas. Potential topics include but are not limited to the following: specific eco-hydrological process understanding (groundwater recharge, snowpack dynamics, intermittent wadi flows, evapotranspiration of crops), quantification and prediction of water resources and uses, impact of water resource management on the sediment transport to the sea, observation issues based on earth observation data and characterization and impact analysis of drought events, and social interactions related to the transfer of research to practice.