Adaptation of standardised (FAO and ASCE) procedures of estimating net longwave and shortwave radiation to Mediterranean greenhouse crops

Daily net shortwave (Sn,g) and longwave (Ln,g) radiation were both measured in six representative Mediterranean greenhouse crop cycles. Daily Sn,g and Ln,g were firstly estimated with the standardised FAO and ASCE procedures for reference surfaces using meteorological data. Daily Sn,g estimated with a seasonal albedo of 0.23 was generally lower than measured values for most crops (RMSE of 0.66 MJ m-2 d-1). Accurate Sn,g estimates were obtained using a seasonal albedo of 0.16 for all the studied crops (RMSE of 0.33 MJ m-2 d-1). Most crops, sown/transplanted at low densities and grown with high-wire production systems over the cold winter period, presented limited vegetative growth. Consequently, in most cases a substantial soil part was uncovered throughout the whole cycle. Daily Ln,g determined with the standardised procedure was substantially underestimated (RMSE of 4.12 MJ m-2 d-1). The Ln,g is affected by the transmission coefficient of the covering material to the longwave radiation (TLR), which varies mostly depending on its optical properties. Incorporating TLR as multiplicative factor into the standardised procedure led to accurate daily Ln,g estimates for all crops, particularly when they reached effective full cover (RMSE of 0.75 MJ m-2 d-1), although Ln,g was still overestimated at the beginning of the cycles, particularly during hot periods. Daily total net radiation (Rn,g), estimated with standardised Sn,g and Ln,g procedures, was much lower than measured values for all cycles, with poor model performance indicators. Daily Rn,g was correctly estimated when standardised Sn,g and Ln,g procedures were adapted to Mediterranean greenhouse crops: pooling all measured data the RMSE was 0.94 MJ m-2 d-1, which improved further when data from the beginning of the cycles were excluded. & COPY; 2023 The Author(s). Published by Elsevier Ltd on behalf of IAgrE. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/