Hydraulic redistribution driven by roots: Modeling and simulation case for the Pantanal

Evapotranspiration is the major component of the water cycle excluding precipitation. Evapotranspiration sub-processes represent important paths of water which have been poorly investigated and may play an important role in the water cycle. Two of these sub-processes are root water uptake (RWU) and root hydraulic redistribution (RHR), which were modelled and numerically explored in this study. Both RWU and RHR were evaluated using the source/sink term in Richards' equation coupled to a vegetation-atmosphere system. This coupling composes a model of water transfer in which the interplay between evapotranspiration and three different root density distributions (exponential, linear and constant scenarios) was simulated to understand, mainly, the influence of rooting systems on RWU and RHR. The results showed that the model consistently described the water dynamics and accurately estimated water fluxes, with evapotranspiration and RWU greater under the constant scenario. RHR contributed, from simulations, up to 21% of the evapotranspiration on a daily basis. Precipitation events may invert the direction of RHR from upward (hydraulic lift) to downward. The last process tends to conserve soil moisture in the root zone. The root systems modified the dynamics of the drainage, being the exponential scenario the greatest contributor to free drainage.