Drought reconstruction based on grape harvest dates for the Czech Lands, 1499-2012

Abstract

The timing of maturity of grapes depends on the weather conditions during the growing season. This study relies on the dependence of harvest dates on the air temperature and dry/wet conditions. Recorded observations show that increases in air temperature and dryness are associated with earlier grape harvests. Documentary data of grape harvests from the Bohemian wine-growing region (mainly northwest of Prague) were combined with mean Standardized Precipitation Evapotranspiration Index (SPEI) series starting in 1841 and ordinary least square regression with subsequent scaling to reconstruct the mean SPEI values for this area for April to August from 1499 to 2012. The reconstructed SPEI series explains 75% of the drought variability since 1841. All dry years that were detected by the reconstructed April-August SPEI values correlate well with years of excellent and good red wine of vintage quality for 1499-1840. A comparison of the reconstructed series with other SPEI reconstructions from the Czech Lands (the recent Czech Republic) based on documentary and instrumental data shows good agreement. The results demonstrate that grape harvest series may be used as a proxy for drought reconstruction in the central European region.