Abstract
The world's population is predicted to exceed nine billion by 2050 and there is increasing concern about the capability of agriculture to feed such a large population. Foresight studies on food security are frequently based on crop yield trends estimated from yield time series provided by national and regional statistical agencies. Various types of statistical models have been proposed for the analysis of yield time series, but the predictive performances of these models have not yet been evaluated in detail. In this study, we present eight statistical models for analyzing yield time series and compare their ability to predict wheat yield at the national and regional scales, using data provided by the Food and Agriculture Organization of the United Nations and by the French Ministry of Agriculture. The Holt-Winters and dynamic linear models performed equally well, giving the most accurate predictions of wheat yield. However, dynamic linear models have two advantages over Holt-Winters models: they can be used to reconstruct past yield trends retrospectively and to analyze uncertainty. The results obtained with dynamic linear models indicated a stagnation of wheat yields in many countries, but the estimated rate of increase of wheat yield remained above 0.06 t ha−1 year−1 in several countries in Europe, Asia, Africa and America, and the estimated values were highly uncertain for several major wheat producing countries. The rate of yield increase differed considerably between French regions, suggesting that efforts to identify the main causes of yield stagnation should focus on a subnational scale.
Highlights
Agriculture will be faced with major challenges in the few decades
We evaluated the predictive capabilities of the models, by calculating root mean square error of prediction (RMSEP) for each model in turn
Examples of fitted values Examples of wheat yield time series obtained in France and Brazil are shown in Figures 1 and 2, respectively
Summary
Agriculture will be faced with major challenges in the few decades. The number of undernourished people was estimated at 868 million for the period 201022012 [1], indicating that food demand has not yet been satisfied in some parts of the world. Yield levels have remained constant or have even declined for some crops [3,4,6214] This is the case for wheat, for which several authors have recently shown much slower rates of yield increase than the period prior to 1990s, with yield stagnation in several countries, including France [3,8,14] and Switzerland [6]. These results have raised significant concerns in the scientific community about the ability of agriculture to feed the world in the future
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