Integrating thermal surface temperature into Penman-Monteith model for estimating evapotranspiration and crop water stress of orange orchard in semi-arid region

This work presents an experimental study and modelling of seasonal actual evapotranspiration (ETa) of an orange orchard, with drip irrigation, in the semi-arid region of Tensift Al Haouz (central Morocco). The experimental study consists of the measurements of different fluxes (mainly latent heat), exchanged between the soil plant -atmosphere continuum. Modelling of ETa is based on the modified Penman-Monteith equation by introducing a simple empirical relationship between the bulk surface resistance (r(s)) and surface temperature (T-s). The proposed model was initially calibrated based on one year of eddy covariance measurements, collected over an orange orchard, and then validated by an independent database collected over three different years. The comparison between measured and modeled ETa showed that the proposed model correctly estimates ETa with an error less than 20%. The proposed approach (relationship between r(c) and T-s) employed in the Penman-Monteith model holds great potential for estimating crop water requirements and crop water stress on an operational basis and at a regional scale, since surface temperature and water status are intimately linked.