Simplifying Sirius: sensitivity analysis and development of a meta-model for wheat yield prediction

A sensitivity analysis and analysis of the structure of the Sirius wheat model has resulted in the development of a simpler meta-model, which produced very similar yield predictions to Sirius of potential and water-limited yields at two locations in the UK, Rothamsted and Edinburgh. This greatly increases the understanding of the nature and consequences of the relationships implicit within Sirius. The analysis showed that the response of wheat crops to climate could be explained using a few simple relationships. The meta-model aggregates the three main Sirius components, the calculation of leaf area index, the soil water balance model and the evapotranspiration calculations, into simpler equations. This results in a requirement for calibration of fewer model parameters and means that weather variables can be provided on a monthly rather than a daily time-step, because the meta-model can use cumulative values of weather variables. Consequently the meta-model is a valuable tool for regional impact assessments when detailed input data are usually not available. Because the meta-model was developed from the analysis of Sirius, rather than from statistical fitting of yield to weather data, it should perform well for other locations in Great Britain and with different management scenarios.