Impacts of hydraulic redistribution on eco-hydrological cycles: A case study over the Amazon basin

Abstract

Hydraulic redistribution (HR) refers to the process of soil water transport through the low-resistance pathway provided by plant roots. It has been observed in field studies and proposed to be one of the processes that enable plants to resist water limitations. However, most land-surface models (LSMs) currently do not include this underground root process. In this study, a HR scheme was incorporated into the Community Land Model version 4.5 (CLM4.5) to investigate the effect of HR on the eco-hydrological cycle. Two paired numerical simulations (with and without the new HR scheme) were conducted for the Tapajos National Forest km83 (BRSa3) site and the Amazon. Simulations for the BRSa3 site in the Amazon showed that HR during the wet season was small, 0.1 mm day–1, transferring water from shallow wet layers to deep dry layers at night; however, HR in the dry season was more obvious, up to 0.3 mm day–1, transferring water from deep wet layers to shallow dry layers at night. By incorporating HR into CLM4.5, the new model increased gross primary production (GPP) and evapotranspiration (ET) by 10% and 15%, respectively, at the BRSa3 site, partly overcoming the underestimation. For the Amazon, regional analysis also revealed that vegetation responses (including GPP and ET) to seasonal drought and the severe drought of 2005 were better captured with the HR scheme incorporated.