Daily forecasting of reference and strawberry crop evapotranspiration in greenhouses in a Mediterranean climate based on solar radiation estimates

This paper presents a method for carrying out daily forecasting of strawberry crop evapotranspiration (ETc), using forecasted greenhouse reference evapotranspiration values (ETogreen) and crop coefficients. ETogreen was estimated using two methods, the first based on incoming solar radiation and the second using the Makkink FAO-24 equation. In both cases, ETogreen was estimated using daily meteorological variables forecasted by the Spanish Meteorology National Agency (AEMET) and then comparing it with the result obtained using measured meteorological data under greenhouse conditions. In addition, values of estimated ETc using measured and forecasted meteorological data were also compared. Lastly, these values were compared with ETc measurements using drainage lysimeters. Incoming solar radiation was estimated from forecasted temperatures and sky cloudiness conditions. Forecasted outdoor and indoor incoming solar radiation values were more accurate using the method based on temperatures. Small differences and high correlations were observed when comparing forecasted and weather measured ETo green and ETc. With respect to forecasted ETo green, the errors were smaller when incoming solar radiation was estimated from forecasted temperature data, especially when using the Makkink equation, with underestimations below 3%. Therefore, these results suggest that the latter method is best suited to the task. Also, the use of forecasted ETc, especially from Makkink FAO24 equation, provided more accurate estimates when compared with lysimeter-measured values.