Parameterization of a bucket model for soil-vegetation-atmosphere modeling under seasonal climatic regimes

Abstract

Abstract. We investigate the potential impact of accounting for seasonal variations in the climatic forcing and using different methods to parameterize the soil water content at field capacity on the water balance components computed by a bucket model (BM). The single-layer BM of Guswa et al. (2002) is employed, whereas the Richards equation (RE) based Soil Water Atmosphere Plant (SWAP) model is used as a benchmark model. The results are analyzed for two differently-textured soils and for some synthetic runs under real-like seasonal weather conditions, using stochasticallygenerated daily rainfall data for a period of 100 years. Since transient soil-moisture dynamics and climatic seasonality play a key role in certain zones of the World, such as in Mediterranean land areas, a specific feature of this study is to test the prediction capability of the bucket model under a condition where seasonal variations in rainfall are not in phase with the variations in plant transpiration. Reference is made to a hydrologic year in which we have a rainy period (starting 1 November and lasting 151 days) where vegetation is basically assumed in a dormant stage, followed by a drier and rainless period with a vegetation regrowth phase. Better agreement between BM and RE-SWAP intercomparison results are obtained when BM is parameterized by a field capacity value determined through the drainage method proposed by Romano and Santini (2002). Depending on the vegetation regrowth or dormant seasons, rainfall variability within a season results in transpiration regimes and soil moisture fluctuations with distinctive features. During the vegetation regrowth season, transpiration exerts a key control on soil water budget with respect to rainfall. During the dormant season of vegetation, the precipitation regime becomes an important climate forcing. Simulations also highlight the occurrence of bimodality in the probability distribution of soil Correspondence to: N. Romano (nunzio.romano@unina.it) moisture during the season when plants are dormant, reflecting that soil, it being of coarser or finer texture, can be preferentially in either wetter or drier states over this period.

An Algebraic Pedotransfer Function to Calculate Standardized in situ Determined Field Capacity

“…Additionally, the concept of "free drainage" is accepted to be vague, "negligible drainage" to be undefined and that two-to-three-day drainage time might not be compatible with negligible drainage (Cassel & Nielsen, 1986;Hillel, 1998;Romano & Santini, 2002;Twarakavi, Sakai, & Simunek, 2009;Assouline & Or, 2014). Due to operating field experiment difficulties, FC is commonly estimated in laboratory from soil samples, such as the water content at a specific suction value, typically 10 kPa or 33 kPa, which is generally considered incompatible with the definition of FC (Hillel, 1998;Twarakavi et al, 2009;Nemes, Pachepsky, & Timlin, 2011;Romano, Palladino, & Chirico, 2011;Ottoni Filho, Ottoni, Oliveira, Macedo, & Reichardt, 2014a). Thus, it is not only the FC concept that is questionable (Cassel & Nielsen, 1986;Assouline & Or, 2014), but also its most usual determination methodology.…”

State and parameter estimation of two land surface models using the ensemble Kalman filter and the particle filter

“…The latter is a prerequisite for characterizing accurately processes such as infiltration, redistribution, root-water uptake, drainage, and groundwater recharge. We refer the interested reader to Romano et al (2011) for a detailed comparison of bucket type and Richards-based vadose zone flow models.…”

An Integrated Approach for the Environmental Characterization of a Wide Area Potentially Contaminated (Southern Italy)

“…The FC value is determined dynamically using a Richards-based numerical model as the average volumetric water content remaining in a soil profile, after having been completely wetted with water and free drainage beyond the root zone has become negligible [42,43]. Instead, the PWP value is estimated using the pedo-transfer function (PTF) of Vereckeen [44].…”

“…This information is suitably embedded in the well-known "available water" (AW) parameter, which is the difference in the volumetric soil-water contents between the field capacity (FC) and permanent wilting point (PWP) conditions in soil (i.e. AW=FC-PWP) [42,43]. In the cases of relatively large land areas, such as the study area considered here, mapping the spatial variations of AW is an effective dynamic indicator to evaluate the efficiency of the selected phytoremediation protocol in the different parts of the territory.…”