Recent studies have demonstrated a direct relation between climate characteristics and vegetation in catchments. For example, plants appear to develop a root system that allows both optimal growth and resistance against region-specific droughts (Gao et al., 2014; Ho et al., 2005). As climatic conditions also affect the way catchments store and release water (i.e., the transit times), we expect a direct relation between vegetation and transit times. To test this hypothesis, we have established a dataset of water balance and stable water isotope data across more than 50 catchments in various climate zones, which will be further expanded over the course of the project. This dataset allows for determining root zone storage capacities and transit time metrics such as the young water fraction (Kirchner, 2016) across catchment scales and climate zones. We will present how transit time metrics vary as a function of root zone storage capacities and how this can be related to catchment and vegetation characteristics and climatic conditions. The results will help understand how changing vegetation cover due to climate and land use change might affect catchment water storage and release in future. We see a vast potential of isotope studies across diverse catchments. We are thus calling for a community effort to provide streamflow isotope data from previous work in a unified framework as a basis for further global analyses using stable water isotopes. Gao, H.; Hrachowitz, M.; Schymanski, S. J.; Fenicia, F.; Sriwongsitanon, N.; Savenije, H. H. G., Climate controls how ecosystems size the root zone storage capacity at catchment scale. Geophysical Research Letters 2014, 41, 7916–7923, doi:10.1002/2014GL061668. Ho, M. D.; Rosas, J. C.; Brown, K. M.; Lynch, J. P., Root architectural tradeoffs for water and phosphorus acquisition. Functional Plant Biology 2005, 32, (8), 737-748. Kirchner, J. W., Aggregation in environmental systems – Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments. Hydrology and Earth System Sciences 2016, 20, (1), 279-297.