Forecasting crop evapotranspiration under standard conditions in precision farming

A new methodology is suggested for forecasting crop evapotranspiration under standard conditions (also referred to as potential evapotranspiration ET p ) by combining VIS-NIR satellite images and numerical weather forecasts. The methodology is proposed for farms where a reliable weather station is operating for assessing current reference evapotranspiration according to FAO Penman-Monteith equation (ET 0-PM ). Measured weather data are exploited for correcting systematic errors in weather forecasts and for locally calibrating Hargreaves-Samani (HS) equation for estimating the reference ET (ET 0-HS ). VIS-NIR crop images and current weather conditions are employed for updating a crop coefficient (K c ), analytically derived as the ratio of crop potential evapotranspiration computed with the Penman-Monteith equation (ET P-PM ) and ET 0-PM . Crop parameters in ET P-PM are assessed by means of albedo and LAI, both retrieved from VIS-NIR images. $\mathrm {E}\mathrm {T}_{\mathrm {P}}$ forecasts are then computed with the HS formula by the product ET P-HS = K c .ET 0-HS . The methodology was applied to two experimental farms in Southern Italy, by employing COSMO-LEPS numerical weather forecasts, LANDSAT 8 and DEIMOS-1 VIS-NIR images. ET P-HS forecasts resulted to be more accurate and precise than ET P-PM forecasts. Differently from ET P-PM forecasts, ET P-HS relies only on temperature forecasts, which are generally less uncertain than the forecasts of the other atmospheric variables, which are required for computing ET P-PM .