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French summer droughts since 1326 CE : A reconstruction based on tree ring cellulose δ18O

Labuhn, Inga LU ; Daux, Valérie; Girardclos, Olivier; Stievenard, Michel; Pierre, Monique and Masson-Delmotte, Valérie (2016) In Climate of the Past 12(5). p.1101-1117
Abstract

The reconstruction of droughts is essential for the understanding of past drought dynamics and can help evaluate future drought scenarios in a changing climate. This article presents a reconstruction of summer droughts in France based on annually resolved, absolutely dated chronologies of oxygen isotope ratios (δ18O) in tree ring cellulose from Quercus spp. Samples were taken from living trees and timber wood from historic buildings at two sites: Fontainebleau (48° 23'N, 2°40'E; 1326-2000 CE) and Angoulême (45°44'N, 0°18'E; 1360-2004 CE). Cellulose δ18O from these sites proved to be a good proxy of summer climate, as the trees were sensitive to temperature and moisture availability. However, offsets in average... (More)

The reconstruction of droughts is essential for the understanding of past drought dynamics and can help evaluate future drought scenarios in a changing climate. This article presents a reconstruction of summer droughts in France based on annually resolved, absolutely dated chronologies of oxygen isotope ratios (δ18O) in tree ring cellulose from Quercus spp. Samples were taken from living trees and timber wood from historic buildings at two sites: Fontainebleau (48° 23'N, 2°40'E; 1326-2000 CE) and Angoulême (45°44'N, 0°18'E; 1360-2004 CE). Cellulose δ18O from these sites proved to be a good proxy of summer climate, as the trees were sensitive to temperature and moisture availability. However, offsets in average δ18O values between tree cohorts necessitated a correction before joining them to the final chronologies. Using the corrected δ18O chronologies, we developed models based on linear regression to reconstruct drought, expressed by the standardized precipitation evapotranspiration index (SPEI). The significant correlations between the SPEI and cellulose δ18O (r ≈-0.70), as well as the verification of the models by independent data support the validity of these reconstructions. At both sites, recent decades are characterized by increasing drought. Fontainebleau displays dominantly wetter conditions during earlier centuries, whereas the current drought intensity is not unprecedented in the Angoulême record. While the δ18O chronologies at the two studied sites are highly correlated during the 19th and 20th centuries, there is a significant decrease in the correlation coefficient between 1600 and 1800 CE, which indicates either a weaker climate sensitivity of the tree ring proxies during this period, or a more heterogeneous climate in the north and the south of France. Future studies of tree ring isotope networks might reveal if the seasonality and spatial patterns of past droughts can explain this decoupling. A regional drought reconstruction based on a combination of the two sites shows good agreement with historical records of grape harvest dates in France, which provide another proxy of summer climate.

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organization
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type
Contribution to journal
publication status
published
subject
in
Climate of the Past
volume
12
issue
5
pages
17 pages
publisher
Copernicus Gesellschaft Mbh
external identifiers
  • scopus:84969549317
  • wos:000378320700001
ISSN
1814-9324
DOI
10.5194/cp-12-1101-2016
language
English
LU publication?
yes
id
bb92846d-bdd3-460d-9579-e896f27e6858
date added to LUP
2016-09-28 14:48:03
date last changed
2017-01-01 08:35:25
@article{bb92846d-bdd3-460d-9579-e896f27e6858,
  abstract     = {<p>The reconstruction of droughts is essential for the understanding of past drought dynamics and can help evaluate future drought scenarios in a changing climate. This article presents a reconstruction of summer droughts in France based on annually resolved, absolutely dated chronologies of oxygen isotope ratios (δ<sup>18</sup>O) in tree ring cellulose from Quercus spp. Samples were taken from living trees and timber wood from historic buildings at two sites: Fontainebleau (48° 23'N, 2°40'E; 1326-2000 CE) and Angoulême (45°44'N, 0°18'E; 1360-2004 CE). Cellulose δ<sup>18</sup>O from these sites proved to be a good proxy of summer climate, as the trees were sensitive to temperature and moisture availability. However, offsets in average δ<sup>18</sup>O values between tree cohorts necessitated a correction before joining them to the final chronologies. Using the corrected δ<sup>18</sup>O chronologies, we developed models based on linear regression to reconstruct drought, expressed by the standardized precipitation evapotranspiration index (SPEI). The significant correlations between the SPEI and cellulose δ<sup>18</sup>O (r ≈-0.70), as well as the verification of the models by independent data support the validity of these reconstructions. At both sites, recent decades are characterized by increasing drought. Fontainebleau displays dominantly wetter conditions during earlier centuries, whereas the current drought intensity is not unprecedented in the Angoulême record. While the δ<sup>18</sup>O chronologies at the two studied sites are highly correlated during the 19th and 20th centuries, there is a significant decrease in the correlation coefficient between 1600 and 1800 CE, which indicates either a weaker climate sensitivity of the tree ring proxies during this period, or a more heterogeneous climate in the north and the south of France. Future studies of tree ring isotope networks might reveal if the seasonality and spatial patterns of past droughts can explain this decoupling. A regional drought reconstruction based on a combination of the two sites shows good agreement with historical records of grape harvest dates in France, which provide another proxy of summer climate.</p>},
  author       = {Labuhn, Inga and Daux, Valérie and Girardclos, Olivier and Stievenard, Michel and Pierre, Monique and Masson-Delmotte, Valérie},
  issn         = {1814-9324},
  language     = {eng},
  month        = {05},
  number       = {5},
  pages        = {1101--1117},
  publisher    = {Copernicus Gesellschaft Mbh},
  series       = {Climate of the Past},
  title        = {French summer droughts since 1326 CE : A reconstruction based on tree ring cellulose δ<sup>18</sup>O},
  url          = {http://dx.doi.org/10.5194/cp-12-1101-2016},
  volume       = {12},
  year         = {2016},
}