Assessing the Impact of Reference Evapotranspiration Models on Decision Support Systems for Irrigation

Reference evapotranspiration (ET0) is a major estimator for crop water requirements predicted by decision support systems for irrigation. However, the impact of different ET0s on the predicted amount of water supply and counts of irrigation events has not been evaluated. Simulations of the Geisenheim Irrigation Scheduling (GS) for vegetable crops with two different ET0s, P2-ET0 and FAO56-ET0, were evaluated to assess exemplarily the impact of ET0s. The sensitivity of both ET0s to local climate conditions was characterized through a random forest analysis, and a linear regression model was used to adjust the original GS by adapting Kc-values to the exchange ET0. For assessing the outcomes of GS irrigation decision, simulations of 173 individual cropping cycles including six vegetable crops over eight years were conducted. After adjusting P2-ET0 Kc-values to FAO56-ET0 Kc-values, there was no impact of the ET0-model on the practical irrigation scheduling with GS. Finally, we discuss that any ET0-model, if adjusted accordingly, might have little impact on similar irrigation systems and provide a method to exchange ET0s.