Performance of the MARS-crop yield forecasting system for the European Union: Assessing accuracy, in-season, and year-to-year improvements from 1993 to 2015.

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.

In-season performance of European Union wheat forecasts during extreme impacts.

Here we assess the quality and in-season development of European wheat (Triticum spp.) yield forecasts during low, medium, and high-yielding years. 440 forecasts were evaluated for 75 wheat forecast years from 1993-2013 for 25 European Union (EU) Member States. By July, years with median yields were accurately forecast with errors below ~2%. Yield forecasts in years with low yields were overestimated by ~10%, while yield forecasts in high-yielding years were underestimated by ~8%. Four-fifths of the lowest yields had a drought or hot driver, a third a wet driver, while a quarter had both. Forecast accuracy of high-yielding years improved gradually during the season, and drought-driven yield reductions were anticipated with lead times of ~2 months. Single, contrasting successive in-season, as well as spatially distant dry and wet extreme synoptic weather systems affected multiple-countries in 2003, '06, '07, '11 and 12', leading to wheat losses up to 8.1 Mt (>40% of total EU loss). In these years, June forecasts (~ 1-month lead-time) underestimated these impacts by 10.4 to 78.4%. To cope with increasingly unprecedented impacts, near-real-time information fusion needs to underpin operational crop yield forecasting to benefit from improved crop modelling, more detailed and frequent earth observations, and faster computation.

Soil quality and vulnerability in a Mediterranean natural ecosystem of Central Italy.

Wet and dry atmospheric depositions and soil chemical and microbiological properties were determined in a Mediterranean natural ecosystem of Central Italy near Rome (Castelporziano Estate). The monitoring of depositions permitted us to quantify the exceedances of S and N compounds (expressed as eqH(+)ha(-1)year(-1)) over the critical loads of acidity. Critical loads, i.e. the quantity of a substance which a part of the environment can tolerate without adverse effects occurring, were determined adopting the level 0 methodology following the UN/ECE Convention on Long-range Transboundary Air Pollution. Deposition data were available for the period 1992-1997, and acidity exceedances were referred to the main vegetation types present in the area. Results showed that most part of the Estate has a medium degree of vulnerability to acidification, and the corresponding risk of acidification deriving from the exceedances of atmospheric deposition was rather low. The study of soil chemical and microbiological properties included mainly total soil organic carbon (SOC), microbial biomass-C, biomass-C/SOC, soil respiration, and metabolic quotient (qCO2). Soil organic C metabolism has been discussed on the basis of the results from eight sampling sites.