19,980 crop yield forecasts have been published for the European Union (EU) Member States (MS) during 1993–2015 using the MARS-Crop Yield Forecasting System (MCYFS). We assess the performance of these forecasts for soft wheat, durum wheat, grain maize, rapeseed, sunflower, potato and sugar beet, and sought to answer three questions. First, how good has the system performed? This was investigated by calculating several accuracy indicators (e.g. the mean absolute percentage error, MAPE) for the first forecasts during a season, forecasts one month pre-harvest, and the end-of-campaign (EOC) forecasts during 2006–2015 using reported yields. Second, do forecasts improve during the season? This was evaluated by comparing the accuracy of the first, the pre-harvest, and the EOC forecasts. Third, have forecasts systematically improved year-to-year? This was quantified by testing whether linear models fitted to the median of the national level absolute relative forecast errors for each crop at EU-12 (EU-27) level from 1993 to 2015 (2006–2015) were characterized by significant negative slopes. Encouragingly, the lowest median MAPE across all crops is obtained for Europe's largest producer, France, equalling 3.73%. Similarly, the highest median MAPE is obtained for Portugal, at 14.37%. Forecasts generally underestimated reported yields, with a systematic underestimation across all MS for soft wheat, rapeseed and sugar beet forecasts. Forecasts generally improve during the growing season; both the forecast error and its variability tend to progressively decrease. This is the case for the cereals, and to a lesser extent for the tuber crops, while seasonal forecast improvements are lower for the oilseed crops. The median EU-12 yield forecasts for rapeseed, potato and sugar beet have significantly (p-value < 0.05) improved from 1993 to 2015. No evidence was found for improvements for the other crops, neither was there any significant improvement in any of the crop forecasts from 2006 to 2015, evaluated at EU-27 level. In the early years of the MCYFS, most of the yield time series were characterized by strong trends; nowadays yield growth has slowed or even plateaued in several MS. In addition, an increased volatility in yield statistics is observed, and while crop yield forecasts tend to improve in a given year, in recent years, there is no evidence of structural improvements that carry-over from year-to-year. This underlines that renewed efforts to improve operational crop yield forecasting are needed, especially in the light of the increasingly variable and occasionally unprecedented climatic conditions impacting the EU's crop production systems.

中文翻译：

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欧盟 MARS 作物产量预测系统的性能：评估 1993 年至 2015 年的准确性、季节性和逐年改进

1993-2015 年间，欧盟 (EU) 成员国 (MS) 使用 MARS-作物产量预测系统 (MCYFS) 发布了 19,980 份作物产量预测。我们评估了这些对软小麦、硬粒小麦、谷物玉米、油菜籽、向日葵、马铃薯和甜菜的预测的表现，并试图回答三个问题。首先，系统的表现如何？这是通过计算几个准确度指标（例如平均绝对百分比误差，MAPE）对一个季节的第一次预测、收获前一个月的预测以及 2006-2015 年期间的活动结束 (EOC) 预测使用报告的产量。其次，预测在本赛季有所改善吗？这是通过比较第一次、收获前和 EOC 预测的准确性来评估的。第三，预测是否有系统地逐年改进？这是通过测试拟合到 1993 年至 2015 年（2006-2015 年）欧盟 12 (EU-27) 水平的每种作物的国家水平绝对相对预测误差中位数的线性模型是否具有显着负斜率的特征来量化。令人鼓舞的是，欧洲最大生产国法国的 MAPE 中值最低，为 3.73%。同样，葡萄牙获得的 MAPE 中位数最高，为 14.37%。预测普遍低估了报告的单产，所有 MS 对软小麦、油菜籽和甜菜的预测都存在系统性低估。预测在生长季节普遍改善；预测误差及其可变性都趋于逐渐减少。谷物是这种情况，块茎作物的情况则较轻，而油籽作物的季节性预测改善幅度较小。从 1993 年到 2015 年，欧盟 12 国对油菜籽、马铃薯和甜菜的产量预测中值显着提高（p 值 < 0.05）。 2006 年至 2015 年的作物预测，在欧盟 27 国水平上进行评估。在 MCYFS 的早期，大多数收益率时间序列的特点是强劲的趋势；如今，在几个 MS 中，产量增长已经放缓甚至趋于平稳。此外，观察到产量统计数据的波动性增加，虽然作物产量预测在特定年份往往会有所改善，但近年来，没有证据表明结构性改善会逐年延续。