BACCHUS temperature reconstruction for the period 16th to 18th centuries from Viennese and Klosterneuburg grape harvest dates

In the scientific project “Klosterneuburg Wine and Climate Change in Lower Austria” (BACCHUS), we focused on developing a grape harvest date (GHD) time series for the period 1523–2007 in the area of and around Vienna, one of the northeasternmost regions in Europe where vines are grown professionally. Since grape harvest dates are strongly influenced by spring to (early) summer temperatures, especially in a vine‐growing region at a climatic border, we found highly significant correlation coefficients between homogenized multiple monthly mean temperatures at Vienna, Hohe Warte, and GHD. For example, correlation values reach −0.76 (p = 0.01) between GHD and April to July mean temperature or −0.79 (p = 0.01) between GHD and May to July mean temperature. This made it possible to reconstruct May to July mean temperatures, starting in 1523. The years from 1775 to 1850 were used as calibration period for determining the temperature sensitivity of GHD, as the running correlation coefficients (10 year moving window) were most pronounced in this period, varying between almost −1 and −0.7 (p = 0.05). We found warm decades in the 16th century, at the beginning of our series, which were as warm as the 1990s. Afterwards the mean May to July temperatures started to drop; the coldest decade of the record was from 1771 to 1780. A constant temperature increase for more than 30 years, as from the 1970s to the present, seems to be unprecedented during the last 470 years.