April–August temperatures in the Czech Lands, 1499–2015, reconstructed from grape-harvest dates

Abstract

Viticulture has long been essential to the commercial and social well-being of parts of the Czech Lands (now the Czech Republic), and detailed records have been kept for centuries of the timing and relative success of the grape crop. Using such documentary data from the Bohemian wine-growing region (mainly northwest of the capital, Prague), series of grape-harvest dates (GHDs) were created for the 1499–2015 period. Because the link between harvest dates and temperatures is strong, GHD series, together with instrumental mean temperature series starting in 1801, were used to reconstruct mean April–August temperatures for the region from 1499 to 2015. Linear regression (LR) and variance scaling (VS) methods were used for calibration and compared in terms of explained variance and their ability to capture extreme values. It emerged that LR does not significantly underestimate temperature variability. However, VS shows far greater capacity to capture extremes. GHDs explain 64 % of temperature variability over the full calibration period. The 1986–2015 period was identified as the warmest 30-year period of the past 514 years, an observation consistent with recent global warming. The highest April–August temperatures appeared in a reconstruction for the year 1540, which was warmer than the next two very warm, and far more recent, seasons in 2003 and 2015. The coldest period occurred at the beginning of the 20th century (1900–1929). The series reconstructed for the Czech Lands is in close agreement with other (central) European reconstructions based on other proxies. The series created here makes an important contribution to a better understanding of long-term spatiotemporal temperature variability in central Europe.