Hydraulic redistribution and its impact on hydroclimatological predictions over North America

Vegetation roots serve as preferential pathways for the movement of moisture from wet to dry soil layers during the night. This passive transport occurs both from upper soil layer to deeper layers during the wet season (‘hydraulic descent') and from the deeper to upper layers during dry seasons (‘hydraulic left') as determined by the moisture gradients. The conductivities of transport through the root system are significantly, often orders of magnitude, larger than that of the surrounding soil resulting in movement of soil-moisture at rates that are substantially larger than that through the soil. This phenomenon is called hydraulic redistribution (HR). HR is generally a nighttime phenomenon when the lack of transpiration demand allows the drier soil-regions to serve as a sink for the moisture transported through the roots. HR allows plant to use deeper layer as a storage whereby during the wet season the water is moved to the deeper layers using roots as the primary conduit and then this water is used during the dry season to meet transpiration demands. To study the impact of HR on hydrometeorological/hydroclimatological predictions we have implemented a model that incorporates soil-root transport processes to the CLM (common Land Model) framework. The parameters of this model are derived as a function of different plant functional types using published data. Simulations are performed over a 30x30 km2 grid covering the North American continent. Studies show that there is significant sensitivity of both precipitation and near surface temperature predictions to HR. Southwestern regions of North America show higher impacts and HR demonstrates substantial remote impacts including that over the oceans.