Evapotranspiration model for semi-arid shrub-lands tested against data from SE Spain

Abstract

A model was developed that predicted evaporation based on combined information on the physiology of overstorey and substrate, micrometeorological conditions and spatial distribution of plants. Predicted evapotranspiration was veri®ed at stand level for Retama sphaerocarpa shrubs, and model parameters were tested to determine their importance in controlling evaporation. Model predictions were compared with evapotranspiration, measured by a Bowen Ratio Energy Balance system (BREB), and transpiration, measured by sap¯ow of the stems of the shrubs in south eastern Spain. Modi®cations made to the original two source clumped model in the tested model signi®cantly improved agreement between predicted surface evapotranspiration rates and rates measured by the Bowen Ratio method. The modi®cations made to the model were improved parameterisation of soil surface conductance, a more detailed description of the radiation balance, and improved parameterisation of the soil aerodynamic conductance terms. Improvements in the soil surface conductance estimates made the most signi®cant change to model predictions, the second two modi®cations showed no signi®cant improvement in prediction of evapotranspiration. A sensitivity analysis indicated that relatively large variations of leaf area index or albedo caused little variation in evapotranspiration during the period measured, whereas variations in soil water content caused large changes in predicted evapotranspiration. Transpiration rates of shrubs (measured and modelled) indicated an independence from surface soil moisture (0±25 cm) supporting the view that R. sphaerocarpa had access to reserves of water deep in the soil which enabled it to survive and grow vigorously in this type of semiarid environment. Thus, it was concluded that land use changes which affect redistribution of water resources (overland and subsurface¯ow) may threaten the stability survival of R. sphaerocarpa stands. #

Facilitation of tree saplings by nurse plants: Microhabitat amelioration or protection against herbivores?

“…Moreover, VPD under shrubs was about half that in open interspaces. These environmental changes can improve the water status of saplings even in the absence of between-microhabitat differences in soil water content, as happened in this study (Holmgren et al 1997;Domingo et al 1999). Although microclimatic differences between microhabitats were not evaluated in winter, shrubs presumably also ameliorate negative temperatures, reducing the risk of frost damage to tissues (Kikvidze & Nakhutsrishvili 1998;Núñez et al 1999).…”

Adsorption of Water Vapor by Bare Soil in an Olive Grove in Southern Spain

“…(9) fitted the results best. In previous studies (McInnes et al 1994;Domingo et al 1999), a power function was used, but it was found that this approach considerably overestimated r a measured at our site, at low wind speeds.…”

Temporal dynamics of soil water balance components in a karst range in southeastern Spain: estimation of potential recharge

“…The technical characteristics of SBIB probes, their calibration as well as successful results with replicates of the same prototype used in different soils, are detailed in different publications (Puigdefábregas et al, , 1998Vidal et al, 1996;Domingo et al, 1999Domingo et al, , 2001Cantón et al, 2001Cantón et al, , 2004. Beginning in July 2003, six probes were installed in a 10 Â 10 m area the eddy tower at a depth of 0.06 m. Moreover, at the end of 2003, six additional y probes were installed in the same place at two depths (three at a depth of 0.06 m and three more at 0.25 m depth), such that y data at two depths are available only from 12 February 2004 to 31 August 2005.…”

“…on the first five days in June, and at 0.25 m only reached 9 %vol. In nearby areas with similar climate, the maximum E occurs in May (Domingo et al, 1999). The seasonal pattern of variation in y, high in spring and late autumn and characteristically low in summer when plants actively take up soil water, is well known (Henninger et al, 1976;Ehrenfeld et al, 1997;Gehrels et al, 1998).…”