Climate and global change impacts on the hydrological cycle, water resources and ecosystems pose great challenges for water and ecosystem management globally. The projected climate change scenarios clearly call for development of new and improved integrated tools for the assessment of climate change impacts on the hydrological cycle, and for assessment of groundwater–surface water interaction. Coastal aquifers and ecosystems are currently under pressure globally from overexploitation and saltwater intrusion. Population growth, climate change and sea level rise will enhance the pressures and the need for protection and sustainable management of water resources and ecosystems for coastal communities in the future.

This special issue of Hydrology and Earth Systems Sciences originates from the EU Interreg IVB project "CLIWAT" on climate change impact on the hydrological cycle and adaptive water management. The CLIWAT project develops and applies new innovative tools for mapping of the current status of groundwater and simulation of future changes to the hydrological cycle based on different climate scenarios and models. The papers of the special issue will focus on describing and demonstrating the applied methods and indicate where improvement and new innovative solutions are required to establish a full and efficient toolbox for evaluating current and future status and climate change impacts on water resources and ecosystems. The necessary tools fall into three groups:

– tools for geological, geophysical and geochemical mapping and characterization of the subsurface including the distribution of freshwater and saltwater;

– tools for assessing climate change impact on the evolution of water resources quantity and quality and ecosystem status (e.g. density-dependent groundwater flow models and integrated hydrological models);

– tools for efficient online visualization and dissemination of, for example, established models and climate change scenario simulations.