Numerical simulations of hydraulic redistribution across climates: The role of the root hydraulic conductivities

Hydraulic redistribution, a process by which vegetation roots redistribute soil moisture, has been recognized as an important mechanism impacting several processes that regulate plant water uptake, energy and water partitioning, and biogeochemical cycling. We analyze how the magnitude of hydraulic redistribution varies across ecosystems that are exposed to different climates and seasonal patterns of incoming shortwave radiation and precipitation. Numerical simulation studies are performed over 10 Ameriflux sites, which show that hydraulic redistribution predictions are significantly influenced by the specified root hydraulic conductivities. We performed sensitivity analyses by considering expected ranges of root conductivities based on previous experimental studies, and found contrasting patterns in energy-limited and water-limited ecosystems. In energy-limited ecosystems, there is a threshold above which high root conductivities enhance hydraulic redistribution with no increase in transpiration, while in water-limited ecosystems increase in root conductivities was always associated with enhancements in both transpiration and hydraulic redistribution. Further we found differences in the magnitude and seasonality of hydraulic redistribution and transpiration across different climates, regulated by interplay between precipitation and transpiration. The annual hydraulic redistribution to transpiration flux ratio (HR/Tr) was significant in Mediterranean climates (HR/Tr ≈ 30%), and in the tropical humid climates (HR/Tr ≈ 15%). However, in the continental climates hydraulic redistribution occurs only during sporadic precipitation events throughout the summer resulting in lower annual magnitudes (HR/Tr < 5%). These results provide more insights for suitable implementation of numerical models to capture belowground processes in eco-hydrology, and enhance our understanding about the variability of hydraulic redistribution across different climates.