Water resources are an important issue in the Mediterranean and semi-arid regions due to water scarcity. The climate of Mediterranean areas (located in the Mediterranean basin but also in Australia, California, Chile and South Africa), and more broadly in semi-arid regions, is characterized by a strong spatio-temporal variability of precipitation. This implies a notable influence of extreme events, flash floods and drought periods which affect water resources management. While these regions record a significant population density, notably in developing countries in the South and East of the Mediterranean basin, they are particularly prone to and are sensitive to climate change, as revealed in several recent reports such as the IPCC or MedECC MAR1. in the past few decades, the expansion of urban areas, changes in land use and agricultural practice and the development of irrigation areas combined with climate change have strongly modified land and water resources. The objective of this session is to discuss the recent advances in Mediterranean and semi-arid hydrology, notably to address the following key challenges:
• the quantification and modelling of threshold effects on runoff genesis, in particular for intermittent and ephemeral streams with strong surface-subsurface interactions in drylands;
• the improvement of forecasting systems for water resources and extreme events, such as flash-floods and droughts;
• the improvement of measurements capabilities with novel approaches, data availability and sharing through regional or international cooperation;
• a better quantification of the impact of water-energy-food nexus on the hydrological cycle, through remote sensing and hydrological modelling;
• gaining a better understanding of the hydrological functioning through regional networking, to assess the potential impacts of climate and land use changes at the regional level.