Root zone storage capacity ( S r ) is an important variable for hydrology and climate studies, as it strongly inﬂuences the hydrological functioning of a catchment and, via evaporation, the local climate. Despite its importance, it remains difﬁcult to obtain a well-founded catchment representative estimate. This study tests the hypothesis that vegetation adapts its S r to create a buffer large enough to sustain the plant during drought conditions of a certain critical strength (with a certain probability of exceedance). Following this method, S r can be estimated from precipitation and evaporative demand data. The results of this ‘‘climate-based method’’ are compared with traditional estimates from soil data for 32 catchments in New Zealand. The results show that the differences between catchments in climate-derived catchment represen- tative S r values are larger than for soil-derived S r values. Using a model experiment, we show that the climate-derived S r can better reproduce hydrological regime signatures for humid catchments; for more arid catchments, the soil and climate methods perform similarly. This makes the climate-based S r a valuable addition for increasing hydrological understanding and reducing hydrological model uncertainty.