Investigating the role of groundwater in mitigating vegetation water stress

Groundwater is often the most persistent water stored in the landscape, which can play a major role in supporting vegetation to mitigate water stress conditions. Yet in most vegetation models, such a role is ignored.
Our objective is to examine the effect of adding the groundwater component on describing vegetation water stress using four variables. Three of these are terrestrial essential climate (TEC) variables; namely actual evapotranspiration (ET), soil moisture (SM), and biomass productivity (BP). The fourth variable is related to vegetation-physiology; solar-induced chlorophyll fluorescence (SIF), which indicates vegetation water stress.
To do so, we propose an integrated eco-hydrological modelling framework that couples the plant-soil-water systems (including groundwater). The coupling between soil and planet has already been realized through the SCOPE-STEMMUS model. SCOPE simulates the radiative transfer in soil, leaves, and vegetation canopies, as well as photosynthesis. STEMMUS is a soil model which simulates the transfer of energy, mass and momentum in the unsaturated zone. Here we focus on adding the groundwater modelling component to the SCOPE-STEMMUS. We add the MODFLOW 6 groundwater flow model which simulates the flow in the saturated zone and its interaction with the surface. The coupling scheme between STEMMUS-SCOPE and MODFLOW 6 (SSM) is realized through the MODFLOW application programming interface, which allows for coupling MODFLOW to other models through exchanging variables without modifying the source codes of the models. The SSM has been tested in a point and grid-scale over the Dinkel catchment, the Netherlands for a year period simulation.
The results showed that groundwater had affected ET, SM, BP, and SIF simulations. Hence, including the groundwater modelling component provides insights into the cause-effect relationships between drought and vegetation water stress and better describes the variability of the TECVs during drought events