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The standard FAO Penman-Monteith (PM-ET o) method for computing the reference evapotranspiration (ET o), in addition to air temperature, needs data on solar radiation or sunshine duration, relative humidity and wind speed which are often lacking and/or do not respect appropriate quality requirements. Hence, in many cases, ET o has to be estimated with limited weather data using maximum and minimum temperature only. Essentially, two procedures are used when no more than temperature data are available: (i) the well-known Hargreaves-Samani equation (HS), or (ii) the PM-ET o method with weather parameters estimated from the limited available data, called PM temperature (PMT) method. The application of these temperature-based approaches often led to contradictory results for various climates and world regions. The data used in the analysis refer to 577 weather stations available through the CLIMWAT database. The results, confirmed by various statistical indicators, emphasized that: (a) in hyper-arid and arid zones, the performance of HS and PMT methods are similar, with root mean square errors (RMSEs) around 0.60-0.65 mm d À1 ; (b) in semi-arid to humid climates, the PMT method produced better results than HS, with RMSE smaller than 0.52 mm d À1 ; (c) the performance of PMT method could be improved when adopting the corrections for aridity/humidity in the estimation of the dew point temperature from minimum temperature data. The spatial elaboration of results indicated high variability of ET o estimates by different methods. Thus, a site-specific analysis using daily datasets of sufficient quality is needed for the validation and calibration of temperature methods for ET o estimate. Maps presenting indicative results on under/over estimation of ET o by both temperature methods may be useful for their more accurate application over different Mediterranean climates.

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Th is work compares the performance of AquaCrop, a crop simulation model developed by FAO, with that of two well established models, CropSyst and WOFOST, in simulating sunfl ower (Helianthus annuus L.) growth under diff erent water regimes in a Mediterranean environment. Th e models diff er in the level of complexity describing crop development, in the main growth modules driving the simulation of biomass growth, and in the number of input parameters. AquaCrop is exclusively based on the water-driven growth module, in that transpiration is converted into biomass through a water productivity (WP) parameter; Cropsyst is based on both water and radiation driven modules, while WOFOST simulates crop growth using a carbon driven approach and fraction of intercepted radiation. Th e data used in the analysis were obtained in fi eld experiments with hybrid Sanbro_MR, performed in a typical Mediterranean area of Southern Italy in 2005 and 2007. Th e models were calibrated on data from a full irrigation treatment in 2007, and were validated on a full irrigation treatment in 2005 and several defi cit irrigation (DI) treatments, including regulated defi cit irrigation (RDI) and rain-fed (RF) conditions. Although AquaCrop required less input information than CropSyst and WOFOST, it performed similarly to them in simulating both biomass and yield at harvesting. Th e use of diff erent numbers of parameters and crop growth modules by the tested models did not infl uence substantially the simulation results. Th erefore, for management purposes and in conditions of limited input information, the use of simpler models should be encouraged.

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