Global patterns of climate controlled root zone storage capacity based on a large sample of catchments

The root zone storage capacity (S_r) is the maximum volume of water in the subsurface that can potentially be accessed by vegetation for transpiration. It influences the seasonality of transpiration as well as fast and slow runoff processes. S_r is heterogeneous as controlled by local climate conditions, which affect vegetation strategies in sizing their root system able to support plant growth and to prevent water shortages. Climate controlled root zone storage capacities can be derived from the maximum water deficit in the root zone based on water balances in gauged catchments. However, root zone parameterization in most global hydrological models does not account for a climate control on root development, being based on look-up tables that prescribe worldwide the same root zone parameters for each vegetation class. These look-up tables are obtained from measurements of rooting structure that are scarce and hardly representative of the ecosystem scale. Several recent studies such as Van Oorschot (2021, https://doi.org/10.5194/esd-12-725-2021) have shown that replacing tabulated S_r values with climate controlled S_r estimates results in improvements in modelling catchment river discharge.

The objective of this research is to investigate global patterns of root zone storage capacity derived from catchment water deficits of a large sample of catchments worldwide. To this aim we explore relations of catchment S_r estimates and catchment climate descriptors such as climatological potential evaporation and precipitation, and catchment vegetation characteristics. These relations at a catchment scale will be used to develop a global coverage of climate controlled of S_r to replace tabulated root zone parameters in global hydrological and climate modelling.