Climate signals in a multispecies tree-ring network from central and southern Italy and reconstruction of the late summer temperatures since the early 1700s

Giovanni Leonelli,Carlo Baroni,Paolo Cherubini,Michele Brunetti,Anna Coppola,Marco Marchetti,Francesco Ripullone,Manuela Pelfini,Emanuele Conte,Giovanna Battipaglia,Maurizio Maugeri,Tiziana Gentilesca,Antonello Provenzale,Marco Borghetti,Valter Maggi,Roberto Tognetti,Maria Cristina Salvatore,Fabio Lombardi

doi:10.5194/cp-13-1451-2017

Abstract

Abstract. A first assessment of the main climatic drivers that modulate the tree-ring width (RW) and maximum latewood density (MXD) along the Italian Peninsula and northeastern Sicily was performed using 27 forest sites, which include conifers (RW and MXD) and broadleaves (only RW). Tree-ring data were compared using the correlation analysis of the monthly and seasonal variables of temperature, precipitation and standardized precipitation index (SPI, used to characterize meteorological droughts) against each species-specific site chronology and against the highly sensitive to climate (HSTC) chronologies (based on selected indexed individual series). We find that climate signals in conifer MXD are stronger and more stable over time than those in conifer and broadleaf RW. In particular, conifer MXD variability is directly influenced by the late summer (August, September) temperature and is inversely influenced by the summer precipitation and droughts (SPI at a timescale of 3 months). The MXD sensitivity to August–September (AS) temperature and to summer drought is mainly driven by the latitudinal gradient of summer precipitation amounts, with sites in the northern Apennines showing stronger climate signals than sites in the south. Conifer RW is influenced by the temperature and drought of the previous summer, whereas broadleaf RW is more influenced by summer precipitation and drought of the current growing season. The reconstruction of the late summer temperatures for the Italian Peninsula for the past 300 years, based on the HSTC chronology of conifer MXD, shows a stable model performance that underlines periods of climatic cooling (and likely also wetter conditions) in 1699, 1740, 1814, 1914 and 1938, and follows well the variability of the instrumental record and of other tree-ring-based reconstructions in the region. Considering a 20-year low-pass-filtered series, the reconstructed temperature record consistently deviates < 1 °C from the instrumental record. This divergence may also be due to the precipitation patterns and drought stresses that influence the tree-ring MXD at our study sites. The reconstructed late summer temperature variability is also linked to summer drought conditions and it is valid for the west–east oriented region including Sardinia, Sicily, the Italian Peninsula and the western Balkan area along the Adriatic coast.

Highlights

Climate reconstructions for periods before instrumental records rely on proxy data from natural archives and on the ability to date them
In order to improve the highly sensitive to climate (HSTC) chronology over the early period showing an expressed population signal (EPS) < ∼ 0.8, we considered the yearly difference of the indexed normalized series from the mean and discarded the early portion of the series exceeding the threshold of 2.5 standard deviations in a given year
We performed the construction of the HSTC chronologies using the individual series from the 12 sites (5 from conifers and 7 from broadleaves; see Table 1, bold values in Table 2 and Sect. 2) for which the site chronologies did not meet the quality standards

Summary

Introduction

Climate reconstructions for periods before instrumental records rely on proxy data from natural archives and on the ability to date them. As a consequence of the poleward expansion of the subtropical dry zones (e.g., Fu et al, 2006), subtropical environments under climate change are already facing strong hydroclimatic changes due to lower precipitation and human exploitation (e.g., in southwestern North America; Seager et al, 2007; Seager and Vecchi, 2010). In these environments (including the Mediterranean region), soil moisture will likely drop, resulting in a contraction of temperate drylands by approximately a third (converting into subtropical drylands), and longer periods of drought in deep soil layers are expected (Schlaepfer et al, 2017). Natural summer fires in the Mediterranean area are expected to increase in frequency over the coming decades as a response to increasingly frequent drought conditions, assuming a lack of additional fire management and prevention measures (Turco et al, 2017)

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Conclusion