Tree-ring indicators of German summer drought over the last millennium

Past natural and future anthropogenic drought variability has and will impact terrestrial ecosystems, agricultural productivity, socio-economic conditions, and public health on various time-scales. In comparison to reconstructed and projected temperature change, much less is known about variations in the hydrological cycle. Here we present 953 living and historical oak (Quercus sp) ring width samples from Central Germany (51-52°N and 9-10°E), that span the AD 996-2005 period and explain ∼18-70% of inter-annual to decadal scale June-September drought variance at the regional-scale. Driest and wettest summers common to the tree-ring proxy and instrumental target data are 1934, 1959, 1996 and 1958, 1966, 1967, respectively. Spatial field correlations are positive with gridded summer hydro-climate over western-central Europe. Increased mid-tropospheric geopotential height (Z500) anomalies over the British Isles appear associated with increased Central German drought, whereas negative Z500 anomalies over Western Europe trigger wet summer extremes due to anomalous moist air advection from the west. Although our study revealed estimates of inter-annual to decadal drought dynamics at the synoptic scale, lower frequency trends remain insecure.