Estimation of air temperature and reference evapotranspiration using MODIS land surface temperature over Greece

Moderate Resolution Imaging Spectroradiometer MODIS, land surface temperature data, during daytime LSTday or night-time LSTnight, were employed for predicting maximum Tmax or minimum Tmin air temperature measured at ground stations, respectively, in order to be used as alternative inputs in minimum data-based reference evapotranspiration ET models in 28 stations in Greece during the growing season May–October. The deviations between daily LSTnight and Tmin were found to be small, but they were greater between LSTday and Tmax. Furthermore, the temperature vegetation index TVX method was employed for achieving more accurate Tmax values from LSTday, after determining the normalized difference vegetation index of a full canopy NDVImax. The TVX method was validated on ‘temporal’ basis, but when the method was tested spatially, the improvement on the Tmax estimates from LSTday was not encouraging, for being used operationally over Greece. Thus, LSTday or LSTnight MODIS data were used as inputs in three ET models [Hargreaves–Samani, Droogers–Allen, and Reference Evapotranspiration Model for Complex Terrains REMCT] and their estimations, as compared with ground-based Penman–Monteith estimates, indicated that the REMCT model achieved the most accurate ET predictions r = 0.93, mean bias error  = 0.44 mm day–1 and root mean square error  = 0.74 mm day–1, which can allow the spatial analysis of ET at higher spatial resolutions in areas with lack of ground temperature data.