Pre-Instrumental Summer Precipitation Variability In Northwestern Greece From A High-Elevation Pinus Heldreichii Network

The spatiotemporal variability of precipitation is of vital importance to Mediterranean ecology and economy, but pre-instrumental changes are not well understood. Here, we present a millennial-length June-July precipitation reconstruction derived from a network of 22 Pinus heldreichii high-elevation sites in the Pindus Mountains of northwestern Greece. Tree-ring width chronologies from these sites cohere exceptionally well over the past several hundred years (r(1467-2015) = 0.64) revealing coherence at inter-annual to centennial timescales across the network. The network mean calibrates significantly against instrumental June-July precipitation over the past 40 years (r(1976-2015) = 0.71), even though no high-elevation observational record is available representing the moist conditions at the treeline above 1,900 m a.s.l. For the final reconstruction, the instrumental target data are adjusted to provide realistic estimates of high-elevation summer rainfall back to 729 CE. The reconstruction contains substantially more low-frequency variability than other high-resolution hydroclimate records from the eastern Mediterranean including extended dry periods from 1,350 to 1,379 CE (39 +/- 4.5 mm) and 913 to 942 (40 +/- 8.4 mm), and moist periods from 862 to 891 (86 +/- 11 mm) and 1,522 to 1,551 (80 +/- 3.5 mm), relative to the long-term mean of 61 mm. The most recent 30-year period from 1986 to 2015 is characterized by above average June-July precipitation (73 +/- 2 mm). Low-frequency changes in summer precipitation are likely related to variations in the position and persistence of storm tracks steering local depressions and causing extensive rainfall (or lack thereof) in high-elevation environments of the Pindus Mountains.