Modelling bulk surface resistance by MODIS data and assessment of MOD16A2 evapotranspiration product in an irrigation district of Southern Italy

In this study, accurate estimates of daily actual evapotranspiration, ETa, were obtained based on the direct Penman-Monteith application, in which the bulk surface resistance term was computed by considering, as main input, daily remotely sensed Land Surface Temperature (LST). In particular, Eddy Covariance measurements of ETa, associated to LST obtained by MODIS time series (MOD11A2) characterized by 8-day resolution, allowed to calibrate a simple bulk surface resistance model, based on two-years of data observations collected in a quite homogeneous irrigation district of Sicily, where olive grove is the main crop. The model was then validated by an independent database collected over four different years.The comparison between measured and modelled actual evapotranspiration fluxes showed that the proposed model is characterized by an acceptable accuracy for practical purposes, with an average RMSE of 0.52 mm d-1 for the whole validation period. In addition, the comparison between ETa values retrieved by the MODIS evapotranspiration product (MOD16A2) and those obtained by the proposed approach, evidenced that to the former are associated the best ETa estimations.The proposed methodology is easily applicable and therefore can be considered as a simple and effective tool to estimate spatial and temporal patterns of actual evapotranspiration, over areas characterized by a level of homogeneity consistent with the MODIS pixel resolution (1 km).Considering that the model was set up for olive crop, further investigations should be focused on other crops under different environmental conditions.