Sensitivity analysis of the rice model WARM in Europe: exploring the effects of different locations, climates and methods of analysis on model sensitivity to crop parameters.

Sensitivity analysis studies how the variation in model outputs can be due to different sources of variation. This issue is addressed, in this study, as an application of sensitivity analysis techniques to a cropmodel in the Mediterranean region. In particular, an application of Morris and Sobol’ sensitivity analysis methods to the ricemodelWARMis presented. The output considered is aboveground biomass at maturity, simulated at five
rice districts of different countries (France, Greece, Italy, Portugal, and Spain) for years characterized by low, intermediate, and high continentality. The total effect index of Sobol’ (that accounts for the total contribution to the output variation due a given parameter) and two Morris indices (mean and standard deviation s of the ratios output changes/parameter variations) were used as sensitivity metrics. Radiation use efficiency (RUE), optimum temperature (Topt), and leaf area index at emergence (LAIini) ranked in most of the combinations site x year as first, second and third most relevant parameters. Exceptionswere observed, depending on the sensitivity method (e.g. LAIini resulted not relevant by the Morris method), or site-continentality pattern (e.g. with intermediate continentality in Spain, LAIini and Topt were second and third ranked; with low continentality in Portugal, RUE was outranked by Topt). Low s values associated with the most relevant parameters indicated limited parameter interactions. The importance of sensitivity analyses by exploring site x climate combinations is discussed as pre-requisite to evaluate either novel crop-modelling approaches or the application of known modelling solutions to conditions not explored previously. The need of developing tools for sensitivity analysis within the modelling environment is also emphasized.