May-July precipitation reconstruction from oak tree-rings for Bohemia (Czech Republic) since AD 1040

This contribution presents a near-millennium-long reconstruction of May-July (MJJ) precipitation for Bohemia, the western part of the recent Czech Republic. A well-replicated chronology of oak (Quercus spp.) tree-ring width (TRW) measurements covering the 1040-2013 period was employed as a high-resolution hydroclimatic proxy. Standardized TRW indices were calibrated to selected grid points from the CRU precipitation database, covering the geographical distribution of the oak data used. The oak TRW chronology explains 34% of MJJ precipitation variability during the 1901-1980 period used for calibration. Although the relationship between oak TRW and target data was relatively stable for this period, the coherence drops significantly beyond it. However, two independent verification periods reveal highly positive reduction of error (RE) and coefficient of efficiency (CE) statistics. Less formal verification based on direct comparison with 14 European proxy-based reconstructions further suggests relatively good agreement in the temporal occurrence of above/below mean late spring-early summer precipitation totals, especially in the 16th-17th centuries. The new MJJ precipitation reconstruction is restricted to inter-annual and inter-decadal variability, which is in line with our understanding of natural precipitation variability. Reconstruction reveals two long periods of low precipitation variability, in the 13th-14th centuries and 1630s-1850s. It also demonstrates that precipitation anomalies of larger amplitude and longer duration occurred in the earlier part of the last millennium than those found in the instrumental period. Negative trends in soil moisture content and gradual changes in annual precipitation distribution leading to higher extremity of precipitation regime may be responsible for the lower sensitivity of oaks to precipitation after the 1980s. The new reconstruction does not indicate any exceptional recent decline in MJJ precipitation.