Abstract
Abstract. The root zone storage capacity (Sr) of vegetation is an important parameter in the hydrological behaviour of a catchment. Traditionally, Sr is derived from soil and vegetation data. However, more recently a new method has been developed that uses climate data to estimate Sr 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 Sr 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 Sr in boreal regions. Relations were assessed between climate-derived Sr values and climate variables (precipitation-potential evaporation rate, mean annual temperature, max snow water equivalent, snow-off date), detailed vegetation characteristics (leaf cover, tree length, root biomass), and vegetation types. The results show that in particular the phase difference between snow-off date and onset of potential evaporation has a large influence on the derived Sr values. Further to this it is found that (non-)coincidence of snow melt and potential evaporation could cause a division between catchments with a high and a low Sr value. It is concluded that the climate-derived root zone storage capacity leads to plausible Sr values in boreal areas and that, apart from climate variables, catchment vegetation characteristics can also be directly linked to the derived Sr values. As the climate-derived Sr 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 boreal regions.
Highlights
The hydrological cycle of boreal regions is changing vastly as a result of climate change (Prowse et al, 2015) and increasing anthropogenic land use activities (Instanes et al, 2016)
It is concluded that the climate-derived root zone storage capacity leads to plausible Sr values in boreal areas and that, apart from climate variables, catchment vegetation characteristics can be directly linked to the derived Sr values
The same can be observed from Fig. 4a: the catchments in the north and mid-boreal regions show a negative correlation between Sr and P /Ep, while in the south boreal region no significant correlation exists: the range in Sr values is large, the variability in P /Ep is small
Summary
The hydrological cycle of boreal regions is changing vastly as a result of climate change (Prowse et al, 2015) and increasing anthropogenic land use activities (Instanes et al, 2016). Predicted changes create climatic conditions at certain higher latitudes, which are similar to those at lower latitudes a few decades earlier (Intergovernmental Panel on Climate Change, 2014). These changes in climate will have an effect on different vegetation types, while at the same time land use activities have been intensified, especially in European countries, and are predicted to increase in the near future due to a “green shift” to a bio-based economy (Golembiewski et al, 2015). The land use changes consist of modifications in actual land use (increase in forest cover), and of more intensive use of forests, including clear cutting, forest trimming, residual harvest and of increasing utilisation of peatland forests as a source for biomass (e.g. Laudon et al, 2011; Nieminen et al, 2017)
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