Assessing the suitability of American National Aeronautics and Space Administration (NASA) agro-climatology archive to predict daily meteorological variables and reference evapotranspiration in Sicily, Italy

- POWER-NASA air temperature are quite well estimated for elevation z < 650 m a.s.l.
- Errors on RH depend on sea distance D (coastal stations), and on z (inland stations).
- POWER-NASA solar radiation generally reproduces the values measured on ground.
- POWER-NASA archive allows suitable ET0 estimates where climate data are missing.

For decades, the importance of evapotranspiration processes has been recognized in many disciplines, including hydrologic and drainage studies, irrigation systems design and management.In this research, the suitability of the Prediction Of Worldwide Energy Resource database published by the American National Aeronautics and Space Administration (POWER-NASA), to estimate daily meteorological variables and ET0 was assessed in Sicily, Italy, for the period 2006-2014, based on ground data measured by a network of climate stations belonging to the regional Agro-meteorological Information Service (SIAS). After comparing the climate data (minimum, Tmin, maximum, Tmax, and average, Tavg, air temperature, relative air humidity, RH, global solar radiation, Rs and wind speed, u) available in both databases, a statistical comparison was carried out on ET0 values estimated according to the Penman Monteith equation in the version proposed by the Food and Agriculture Organization (FAO-56 PM).The analysis showed that correlations between air temperature and relative air humidity from both databases are affected by elevation of the weather stations and the distance from the sea. In addition, ET0 values estimated with POWER-NASA database were generally comparable to those obtained by using the SIAS records, with RMSE values ranging between 0.68 and 1.27 mm d−1 and MBE varying between −0.39 and 0.73 mm d−1. The greatest differences in ET0 values are due to the resolution of POWER-NASA archive (1° latitude by 1° longitude), that cannot detect the actual spatial variability observed on ground, as well as to inaccurate estimations of relative air humidity occurring for the coastal weather stations as well as of the air temperature for those inland stations characterized by high elevations. However, the achieved results support the possibility of obtaining suitable estimates of daily ET0 based on the POWER-NASA agro-climatology archive, even to other Mediterranean countries where most of the climate variables are not measured.