Relaciones agua-suelo-vegetación.-Influence of soil moisture on the modelling of evapotranspiration in sparse vegetation

Abstract

ABSTRACT This work analyses the relevance of soil water content (θ) on the estimation of actual evapotranspiration (λE) in sparse vegetated areas. This importance is evaluated through the effect of the θ heterogeneity, both vertical and horizontal (differentiating between bare soil (bs) and soil under vegetation (s)), on λE estimates. A clumped evapotranspiration model (CM) that considers vegetation (p), bs and s as sources of evaporation, was used. This model estimates λE of the whole vegetated area, as well as the contribution of each source. The field site is a sparse-vegetated patch of Anthyllis cytisoides (L.) located in the instrumental area of Rambla Honda in Tabernas (Almería), run by the Arid Zones Experimental Station (CSIC). Values of θ measured at three depths (0.02 m, 0.05 m and 0.15 m) and the averaged for the whole 0.15 m soil profile were used to calculate parametric equations of surface soil resistances bs rs and s rs and the surface leaf conductance ls g . The parametric equations were introduced in the CM and the λE estimates obtained were compared with measured values from an Eddy covariance system. Results showed that θ has an important effect on the estimates of bs and s contributions. The modelled λE that provided the best results were obtained when bs rs and s rs were parameterised with θ measured at the surface at 0.02 m (RMSE = 0.2 mm day-1), while the worst estimates were obtained when using θ measured deeper (RMSE = 0.75 mm day-1).