Understanding variability in root zone storage capacity in boreal regions

Abstract. The root zone storage capacity ( S r ) of vegetation is an important parameter in the hydrological behaviour of a catchment. Traditionally, S r is derived from soil and vegetation data. However, more recently a new method has been developed that uses climate data to estimate S r based on the assumption that vegetation adapts its root zone storage capacity to overcome dry periods. This method also enables one to take into account temporal variability of derived S r values resulting from changes in climate or land cover. The current study applies this new method in 64 catchments in Finland to investigate the reasons for variability in S r in borealregions. Relations were assessed between climate-derived S r values and climate variables (precipitation- potential evaporationrate, mean annual temperature, max snow water equivalent, snow-off date), detailed vegetation characteristics (leaf cover, treelength, root biomass), and vegetation types. The results show that in particular the phase difference between snow-off date and onset of potential evaporationhas a large influence on the derived S r values. Further to this it is found that (non-)coincidence of snow melt and potential evaporationcould cause a division between catchments with a high and a low S r value. It is concluded that the climate-derived root zone storage capacity leads to plausible S r values in borealareas and that, apart from climate variables, catchment vegetation characteristics can also be directly linked to the derived S r values. As the climate-derived S r enables incorporating climatic and vegetation conditions in a hydrological parameter, it could be beneficial to assess the effects of changing climate and environmental conditions in borealregions.