Simulation of willow short‐rotation forest evaporation using a modified Shuttleworth–Wallace approach

Abstract

Abstract:Evaporation from a willow short-rotation forest was analysed using a modified version of the Shuttleworth-Wallace model. The main modification consisted of a two-layer soil module, which enabled soil surface resistance to be calculated as a function of the wetness of the top soil. Introduction of the threshold value of the leaf area index when scaling up from the leaf to the canopy resistance resulted in improvement to the simulated evaporation. The analysis was concentrated mainly on the 1988 season (May-October) when total evaporation was measured by the energy balance/Bowen ratio method throughout the growing season, covering all stages of canopy development. At the beginning of the 1994 season, soil evaporation were also measured with a ventilated chamber system. The general seasonal dynamics of the evaporation were fairly well simulated with the model. The largest deviation between measured and simulated evaporation occurred in June, when the model underestimated evaporation by about 1 mm day 1 . The model underestimated also in May but not as much as in June. In September and October the performance of the model was very good. For 130 days of the period May-October the cumulated measured evaporation was 364 mm and the simulated evaporation for the same days was 362 mm. It should be pointed out that this result was obtained without calibrating the model against the measured evaporation. The total simulated evaporation for the season was 450 mm with transpiration constituting 298 mm (66%), soil evaporation 102 mm (23%) and interception evaporation 50 mm (11%). The sensitivity analysis showed, in general, that simulated evaporation was most sensitive to changes in resistances when the leaf area index was smallest, i.e. under non-closed canopy conditions. Changes in stomatal resistance, which is one of the most sensitive parameters, with associated changes in canopy transpiration, resulted in a negative feedback effect on soil evaporation. This reduced the total evaporation's sensitivity to stomatal resistance. This type of interaction between canopy and soil or undergrowth fluxes has been observed in other studies as well.

Spatiotemporal variations of T/ET (the ratio of transpiration to evapotranspiration) in three forests of Eastern China

“…For example, the portion of EI in ET in temperate forest in a forest in Finland (Ge et al, 2011) and Sweden (Iritz et al, 2001) was around 10%, which had similar climate and vegetation status as CBS, while EI occupied about 15.79% of ET at a tropical rainforest (Kume et al, 2011), which had more precipitation than the two subtropical forests but similar vegetation status. In addition, the simulated T/ET were comparable with the measured ones ( Fig.…”

“…Shuttleworth-Wallace model (S-W model) is the first model designed for ET partition, which is a physically-based combination model based on Penman-Monteith equation (Shuttleworth and Wallace, 1985). S-W model has also been regarded as an accurate model and the foundation of other ET partition models, which provides a validation for other models (Kool et al, 2014) and has been widely used (Hu et al, 2009;Iritz et al, 2001;Kato et al, 2004), while there have been no attempt in using S-W model to partition ET into its components at forests of China, which occupied an important portion in global forests (FAO, 2010). China has conducted eddy covariance measurements since 2003 at three forests along the north-south transect of Eastern China (NSTEC), which experiences apparent decreasing temperature and precipitation gradients with the increasing latitude .…”

Surface energy balance model of transpiration from variable canopy cover and evaporation from residue-covered or bare soil systems: model evaluation

“…These extended approaches provide the potential for modeling ET for the entire range of plant cover and the ability of partitioning ET between crop transpiration and soil evaporation. The advantage of these models has been recognized by several authors (e.g., Shuttleworth and Gurney 1990;Farahani and Ahuja 1996;Stannard 1993;Massman 1992;Gardiol et al 2003;Iritz et al 2001;Tourula and Heikinheimo 1998;Ortega-Farias et al 2007;Anadranistakis et al 2000;Alves and Cameira 2002;Lafleur and Rouse 1990). Results from using multiple-layer models are encouraging, in general, and these models performed satisfactorily for a large range of canopy cover than single-layer models.…”

Evapotranspiration of Partially Vegetated Surfaces

“…Surface resistances regulate the heat and mass transfer in plant and soil surfaces, and aerodynamic resistances regulate fluxes between the surface and the atmospheric boundary layer. Several studies have evaluated the performance of the S-W model to estimate evapotranspiration (Farahani & Baush,1995;Stannard, 1993;Lafleur & Rouse, 1990;Farahani & Ahuja, 1996;Iritz et al 2001;Tourula & Heikinheimo, 1998;Anadranistakis et al, 2000;Ortega-Farias et al, 2007). Field tests of the model have shown promising results for a wide range of both agricultural and non-agricultural vegetation.…”

“…Using the potential of the S-W model to partition transpiration and evaporation, Farahani and Ahuja (1996) extended the model to include the effects of crop residues on soil evaporation by the inclusion of a partially covered soil area and partitioning evaporation between the bare and residue-covered areas. Iritz et al (2001) applied a modified version of the S-W model to estimate evapotranspiration for a forest. The main modification consisted of a two-layer soil module, which enabled soil surface resistance to be calculated as a function of the wetness of the top soil.…”