Time series analysis of environmental tracers combined with hydrologicalobservations and models provides insight into processes of runoffgenerationand groundwater recharge. The natural integration of temporal andspatialvariability of stable isotope data (oxygen-18, deuterium) at differentscales of hydrological systems can be used as a basis for the study ofcatchment response to climate variability and change. This approach isdemonstrated using monitoring data of runoff, groundwater levels, stableisotope and chemical composition at the meso-scale Dreisam catchment(BlackForrest, Germany). The observations reveal that the serious hydrologicdrought in summer 2003 was preceded by deviations from the hydrologicandisotopic regime. The departure from a regular seasonal variation startedalready during winter and spring 2002/2003 - half a year before thehydrological drought became obvious. Isotope data suggest that the lackofintense groundwater recharge from snow-melt due to a warmer than averagewinter season aggravated the drought of 2003. Further investigationsshoweda scale-dependent and event-dependent percentage of snow-meltcontributionsto runoff and groundwater recharge. As a result the role of snow-meltforgroundwater regimes needs to be reviewed. Climate changes resulting indifferent snow-melt conditions might have non-linear impacts on thewaterbalance of catchments and aquifers. Environmental tracers providemethodsfor the integrated study of these processes at different scales.