Due to climate change, water availability for different uses such as domestic water supply, hydropower production and agricultural irrigation could be significantly reduced in the near future mainly in regions with arid and semi-arid climate. Precipitation data in the form of time series from different stations in South East Europe (SEE) as well as results from global atmospheric circulation models indicate that climate change will reduce water availability in this part of the Mediterranean. In this presentation the coupling of hydrological, hydraulic and climate change models is suggested in order to explore the impact of climate change on water resources at the river basin level. The methodology is illustrated for the Mesta/Nestos river basin, which is shared between Bulgaria and Greece. The case study is part of the worldwide UNESCO-HELP initiative.