Catchment‐scale Richards equation‐based modeling of evapotranspiration via boundary condition switching and root water uptake schemes. Issue 7 (27th July 2015)

• Record Type: Journal Article
• Authors: Camporese, Matteo; Daly, Edoardo; Paniconi, Claudio
• Is Part Of: Water resources research. Volume 51:Issue 7(2015:Jul.)
• Page Start: 5756
• Page End: 5771
• Publication Date: 2015-07-27
• Subjects: Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2015WR017139
• Languages: English
• ISSNs: 0043-1397

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>In arid and semiarid climate catchments, where annual evapotranspiration (<italic>ET</italic>) and rainfall are typically comparable, modeling <italic>ET</italic> is important for proper assessment of water availability and sustainable land use management. The aim of the present study is to assess different parsimonious schemes for representing <italic>ET</italic> in a process‐based model of coupled surface and subsurface flow. A simplified method for computing <italic>ET</italic> based on a switching procedure for the boundary conditions of the Richards equation at the soil surface is compared to a sink term approach that includes root water uptake, root distribution, root water compensation, and water and oxygen stress. The study site for the analysis is a small pasture catchment in southeastern Australia. A comprehensive sensitivity analysis carried out on the parameters of the sink term shows that the maximum root depth is the dominant control on catchment‐scale <italic>ET</italic> and streamflow. Comparison with the boundary condition switching method demonstrates that this simpler scheme (only one parameter) can successfully reproduce <italic>ET</italic> when the vegetation root depth is shallow (not exceeding approximately 50 cm). For deeper rooting systems, the switching scheme fails to match the <italic>ET</italic> fluxes and is affected by numerical artifacts, generating physically unrealistic soil moisture dynamics. It is further shown that when transpiration is the dominant contribution to <italic>ET</italic>, the inclusion of oxygen stress and root water compensation in the model can have a considerable effect on the estimation of both <italic>ET</italic> and streamflow; this is mostly due to the water fluxes associated with the riparian zone.</p> </abstract>