Wine must yields as indicators of May to July climate in Europe, 1416–1988

Abstract. Narrative historical records of wine production in Central Europe date back to 1200. The extent to which such data can be used as proxy data for summer temperatures is being explored. Here, we investigated taxes paid to the authorities in the French-Luxembourg Moselle region, Germany and the Swiss Plateau over the last few centuries drawing on 11 regional series from the early 15th merged into three supra-regional series: (1) the Moselle series, starting in 1416 and consisting of data from the former city-republic of Metz (France) and the Grand Duchy of Luxembourg; (2) the series for Germany, starting in 1511 and mainly originating from the former city-state of Heilbronn; and (3) the third series, starting in 1529 and representing production on the Swiss Plateau. The residuals of the supra-regional yield series were averaged, divided into seven classes, and multiplied by five quality classes. Yield quality indices (YQI) varying between 35 (large and excellent) and 1 (small and undrinkable) century to 1988. We detrended the data to compensate for longer-term biases. The homogenised series were significantly correlated with temperatures between May and July. Regression analysis of the composite series revealed that yield and quality primarily depend on the climate conditions from May to July as well as on those in June of the previous year. Crops with a YQI > 28 (rated "good" by traditional winegrowers) were related to above-average May–July temperatures, early grape harvest dates and high tree-ring maximum latewood density resulting from frequent anticyclonic weather situations. Crops with YQI > 10 could not be uncritically assigned to cold summers since winter, and spring frosts often reduced yields without affecting quality. Severe crop failures sometimes triggered witch hunts. In summary, narrative evidence on wine production allows reconstructions based on tree-rings to be specified and verified.