Modeling the monthly mean soil-water balance with a statistical-dynamical ecohydrology model as coupled to a two-component canopy model

Abstract

Abstract. The statistical-dynamical annual water balance model of Eagleson (1978) is a pioneering work in the analysis of climate, soil and vegetation interactions. This paper describes several enhancements and modifications to the model that improve its physical realism at the expense of its mathematical elegance and analytical tractability. In particular, the analytical solutions for the root zone fluxes are re-derived using separate potential rates of transpiration and bare-soil evaporation. Those potential rates, along with the rate of evaporation from canopy interception, are calculated using the two-component Shuttleworth-Wallace (1985) canopy model. In addition, the soil column is divided into two layers, with the upper layer representing the dynamic root zone. The resulting ability to account for changes in root-zone water storage allows for implementation at the monthly timescale. This new version of the Eagleson model is coined the Statistical-Dynamical Ecohydrology Model (SDEM). The ability of the SDEM to capture the seasonal dynamics of the local-scale soil-water balance is demonstrated for two grassland sites in the US Great Plains. Sensitivity of the results to variations in peak green leaf area index (LAI) suggests that the mean peak green LAI is determined by some minimum in root zone soil moisture during the growing season. That minimum appears to be close to the soil matric potential at which the dominant grass species begins to experience water stress and well above the wilting point, thereby suggesting an ecological optimality hypothesis in which the need to avoid water-stress-induced leaf abscission is balanced by the maximization of carbon assimilation (and associated transpiration). Finally, analysis of the sensitivity of model-determined peak green LAI to soil texture shows that the coupled model is able to reproCorrespondence to: J. A. Ramírez (ramirez@engr.colostate.edu) duce the so-called "inverse texture effect", which consists of the observation that natural vegetation in dry climates tends to be most productive in sandier soils despite their lower water holding capacity. Although the determination of LAI based on complete or near-complete utilization of soil moisture is not a new approach in ecohydrology, this paper demonstrates its use for the first time with a new monthly statistical-dynamical model of the water balance. Accordingly, the SDEM provides a new framework for studying the controls of soil texture and climate on vegetation density and evapotranspiration.

Evapotranspiration Partition and Crop Coefficients of Tifton 85 Bermudagrass as Affected by the Frequency of Cuttings. Application of the FAO56 Dual Kc Model

“…A small E s /ET c ratio of 13% was also referred to for native grasslands, however for arid conditions [49]. High transpiration ratios, but smaller than those observed in this study, were reported by various authors [15,46,50], namely influenced by soil texture [45]. Transpiration ratios for tropical and temperate grasslands of 62 ± 19% and 57 ± 19%, respectively, were reported by Schlesinger and Jasechko [60], therefore values with upper limits that are smaller than those observed in this study.…”

“…It is very precise when an appropriate parameterization is achieved, which is a quite demanding task that limits the operational use of SW in agricultural water management practice; various examples of the application of SW to grass are reported in the literature [44,45]. Other double source models were applied to grass, such as the one reported by Huang et al [46], which is based upon the estimation of gross ecosystem productivity using CO 2 fluxes observed with the eddy covariance method, and that proposed by Wang and Yamanaka [47], which consists of a modification of the SW model.…”

Sequential assimilation of satellite-derived vegetation and soil moisture products using SURFEX_v8.0: LDAS-Monde assessment over the Euro-Mediterranean area

“…Loew et al, 2013;Albergel et al, 2013a, b) and in situ measurements (Dorigo et al, 2015. Lambin et al (1999) found that the GEOV1 LAI dataset is also consistent over time and can be used, for example, for detection of change and for providing information on shifting trends or trajectories in land use and cover change. To verify the results from literature for the spatial and temporal domain considered in this study, a consistency evaluation both for SSM and LAI against the open-loop experiment has been performed.…”

Regional Equivalent Water Thickness Modeling from Remote Sensing across a Tree Cover/LAI Gradient in Mediterranean Forests of Northern Tunisia

“…Methods were then proposed to overcome this fact by modifying the linear regression between VI and EWT variables, accounting for the seasonal and interannual vegetation variability [4,30,35], as well as the species mixture and their related biophysical properties [36]. Considering that leaf area index (LAI) is an integrated proxy for canopy density and ecosystem water content capacity according to the ecohydrological equilibrium theory [37], canopy variables represented by LAI are also important parameters affecting the retrieval of water vegetation status from remote sensing vegetation indexes. Based on the Prospect simulation model [38] combined with canopy models, Ceccato et al [20] showed that GVMI is suitable for retrieving vegetation water content when the LAI is equal to or greater than two due to the effect of soil background.…”