Historical vintage descriptions from Luxembourg - an indicator for the climatic conditions in the past?

Verbal vintage descriptions in a historical wine chronicle (809-1904) of the Luxembourgish winegrowing region were assigned to five wine quality and three wine quantity classes. To calibrate models describing the impact of the seasonal heat consumption on wine quality and quantity, instrumental records from Luxembourg-City in a reference period (1854-1885) and the associated vintage quality and quantity classes were correlated. Dummy regression models showed, that in the reference period the wine quality classes assigned were significantly correlated with the annual modified heliothermic index values (representing the heat consumption) (R2adj.= 0.55, p = 0.0002); whereas, the incorporation of the wine quantity as additional predictor variable did not significantly improve model output. Based on linear correlations between annual thermal conditions and wine quality descriptions, average April-September temperatures were reconstructed for the period 1200-1904. Running averages calculated using LOESS smoothing showed that periods with cooler and warmer climatic conditions alternated in the past centuries. Even though a precise reconstruction of the annual temperature conditions solely based on vintage descriptions is not possible due to the broad set of potentially interfering effects, long-term climatic trends described in the literature such as the Medieval Climate Optimum and the Little Ice Age could be retrieved