Two millennia of Main region (southern Germany) hydroclimate variability

Abstract

A reconstruction of hydroclimate with an annual resolution covering millennia for a geographically limited region in continental Europe significantly improves our knowledge of past climate dynamics. With the use of an extensive collection of oak ring-width series (Quercus robur and Quercus petraea) from living trees, historic timbers and subfossil alluvial wood deposits from the Main River region in southern Germany, a regional, 2000-year long, seasonally resolved hydroclimate reconstruction for the Main region has been developed. Climate-growth response analysis has been performed with daily climate records from AD 1900 onwards. To test the stability of the developed transfer function, a bootstrapped transfer function stability test (BTFS) as well as a classical calibration/verification approach have been implemented to study climate-growth model performance. Living oak trees from the Main River region show a significant sensitivity to the precipitation sum from 26 February to 6 July (spring to midsummer) during the full (r=0.49, p<0.01, N=116) and split (r=0.58, p<0.01, N=58) calibration periods. BTFS confirmed the stability of the developed transfer function. The developed precipitation reconstruction reveals high variability on a high- to mid-frequency scale during the past two millennia. Very dry spring to midsummer seasons lasting multiple years appeared in the decades AD 500/510s, 940s, 1170s, 1390s and 1160s. At the end of the AD 330s, a persistent multi-year drought with drastically reduced rainfall (with regard to 1901–2000) could be identified, which was the driest decade over the past 2000 years in this region. In the AD 550s, 1050s, 1310s and 1480s, multi-year periods with high rainfall hit the Main region. In spring to midsummer of AD 338, precipitation was reduced by ∼38 % and in AD 357 it increased by ∼39 %. The presented hydroclimate reconstruction and its comparison to other records reveal interesting insights into the hydroclimate dynamics of the geographically limited area over the Common Era, in addition to revealing noticeable temporal differences.