Intercode comparisons for simulating water balance of surficial sediments in semiarid regions

Abstract

[1] Near-surface water balance modeling is often used to evaluate land-atmosphere interactions, deep drainage, and groundwater recharge. The purpose of this study was to compare water balance simulation results from seven different codes, HELP, HYDRUS-1D, SHAW, SoilCover, SWIM, UNSAT-H, and VS2DTI, using 1-3 year water balance monitoring data from nonvegetated engineered covers (3 m deep) in warm (Texas) and cold (Idaho) desert regions. Simulation results from most codes were similar and reasonably approximated measured water balance components. Simulation of infiltrationexcess runoff was a problem for all codes. Annual drainage was estimated to within ±64% by most codes. Outliers result from the modeling approach (storage routing versus Richards' equation), upper boundary condition during precipitation, lower boundary condition (seepage face versus unit gradient), and water retention function (van Genuchten versus Brooks and Corey). A unique aspect of the code comparison study was the ability to explain the outliers by incorporating the simulation approaches (boundary conditions or hydraulic parameters) used in the outlying codes in a single code and comparing the results of the modified and unmodified code. This approach overcomes the criticism that valid code comparisons are infeasible because of large numbers of differences among codes. The code comparison study identified important factors for simulating the near-surface water balance.

Potential climate change effects on groundwater recharge in the High Plains Aquifer, USA

“…It uses the Penman-Monteith equation [Monteith, 1965] for simulation of the energy balance, and this allows ET to be affected by dynamic vegetation growth responding to availability of water, nutrients, and light [Wu et al, 1994]. WAVES uses Richards' equation for modeling unsaturated flow, which has the advantage of allowing water movement to be simulated under relatively dry conditions [Scanlon et al, 2002]. WAVES has been shown to be able to reproduce measured field data in a variety of environments [Zhang et al, 1996[Zhang et al, , 1999Wang et al, 2001;Crosbie et al, 2008] and has previously been used in modeling recharge under future climate scenarios [Green et al, 2007;Crosbie et al, 2010bCrosbie et al, , 2013.…”

Sensitivity of groundwater recharge using climatic analogues and HYDRUS-1D

“…The HYDRUS-1D model structure was previously compared to six other models by Scanlon et al (2002). Drainage measured in a lysimeter experiment could be estimated within ±64% by most codes.…”

“…In the present study, with analogue stations from a subtropical climate class, a not too coarse soil texture and the presence of groundwater at relatively shallow depth caused matric potential driven flow to be an important factor for the water balance. Using a capacity-type model would probably overestimate drainage and groundwater recharge (Scanlon et al, 2002). Under a forest cover, van der Salm et al …”

“…Consequently, such soil/atmospheric and vegetation responses and feedback mechanisms may also influence the net outcome in water savings, for example increases in the The HYDRUS-1D model structure was previously compared to six other models by Scanlon et al (2002). Drainage measured in a lysimeter experiment could be estimated within ±64 % by most codes.…”

“…Drainage measured in a lysimeter experiment could be estimated within ±64 % by most codes. Scanlon et al (2002) showed that divergences in simulation outputs could be attributed to (i) modelling concept (Richards equation vs. capacity model); (ii) upper boundary condition (ET 0 during precipitation set to zero vs. substracted from P ) and time discretization of precipitation (cf. also Mertens et al, 2002); (iii) functional form of water retention functions (Brooks and Corey vs. van Genuchten); and (iv) type of lower boundary condition (seepage face vs. unit gradient for the lysimeter study).…”