Improvement of FAO - 56 model to estimate transpiration fluxes of 1 drought tolerant crops under soil water deficit : An application for 2 olive groves

16 Agro-hydrological models are considered an economic and simple tool to quantify crop water 17 requirements. In the last two decades, agro-hydrological physically based models have been 18 developed to simulate mass and energy exchange processes in the soil-plant-atmosphere 19 system. Although very reliable, due to the high number of required variables, simplified 20 models have been proposed to quantify crop water consumes. 21 The main aim of the paper is to propose an amendment of FAO-56 spreadsheet program in 22 order to introduce a more realistic shape of the stress function, valid for mature olive orchards 23 (Olea europaea L.). The modified model is successively validated by means of the 24 comparison between measured and simulated soil water contents and actual transpiration 25 fluxes. These outputs are finally compared with those obtained with the original version of the 26 model. 27 Experiments also allowed assessing the ability of simulated crop water stress coefficients to 28 explain the actual water stress conditions evaluated on the basis of measured relative 29 transpirations and midday stem water potentials. 30 The results show that the modified model significantly improves the estimation of actual crop 31 transpiration fluxes and soil water contents under soil water deficit conditions, according to 32 the RMSEs associated to the revised model, resulting significantly higher than the 33 corresponding values obtained with the original version. 34