LysimeterGEO for modelling soil-vegetation-atmosphere 1D system in the Critical Zone

Measuring and modelling of water and solute fluxes in the Critical Zone across soil-vegetation-atmosphere system is nowadays a very important challenge because of the complexity of both soil and plants. Considering the one-dimensional problem, we implement a virtual lysimeter model, LysimeterGEO, in which we coupled infiltration and evapotranspiration by using stress factor (Jarvis, 1976; Ball et al., 1987), with which we can compute effective evapotranspiration and remove it from Richards’ equation balance (Casulli and Zanolli, 2010).

As regards the IT implementation, LysimeterGEO is a system of components built upon the Object Modelling System v3 (OMS3). The infiltration component of the virtual lysimeter is WHETGEO 1D - Water, Heat and Transport in GEOframe (Tubini N. 2021), which solves the mass and energy balance for the one-dimensional case. The mass balance is represented by the Richards equation and the non-linear system is solved using the nested Newton algorithm (Casulli and Zanolli, 2010). Evapotranspiration flows are instead estimated using the GEOframe-Prospero model (Bottazzi M. 2020) which estimates the effective transpiration through the equilibrium temperature of the canopy as a function of the stomatal conductance. Finally, the transpiration is calculated starting from the method of Schymanski and Or (2017) and modified by including the dependence on the transpiring surface, the model of conductance of the stomata, as well as the conservation of mass. In LysimeterGEO the interaction between infiltration and evapotranspiration is made possible by BrokerGEO component (D’Amato C. 2021), which computes the water stress factor for vegetation by using Jarvis or Ball-Berry model. BrokerGEO computes the water stress factor considering the water content information by WHETGEO in each control volumes of the soil column discretization. Moreover, it computes a representative water stress factor for the whole column of soil for the evapotranspiration component. Finally, the density root distribution is considered to remove water into the soil used for evapotranspiration flows.

The modelling of water and solute fluxes across soil-vegetation-atmosphere is made possible by implementation of travel times of waters within vegetation, the growing of the roots and in general the growing of the plants. The idea of a joint infiltration-evapotranspiration model allows us to investigate also problems related to radical growth and the different effect of roots on vegetation. Furthermore, the implementation of travel times on a vegetation scale allows a careful analysis of the behaviour of the same as the soil moisture conditions vary.