Publication issue des travaux du projet PLUIES-TIBET.

Les auteurs ont étudié la largeur des cernes d'arbres sur une période de 500 ans dans deux régions du plateau tibétain de topologie contrastées distantes de 50 km, et analysé les liens avec certains paramètres climatiques (précipitations, indices de sécheresse, débits des cours d'eau).

Alors que des corrélations significatives entre la taille des cernes, les précipitations locales entre avril et juin, l'indice de sécheresse et les débits des cours d'eau, sont observées entre 1948/1954 et 1970, ces corrélations disparaissent pour la période 1970-1998.

Ces résultats appellent à la prudence lors de l'utilisation de la taille des cernes des arbres pour les reconstructions paléoclimatiques.

Résumé en anglais

An unstable tree-growth response to climate in two 500 year chronologies, North Eastern Qinghai-Tibetan Plateau

Two new Juniper tree-ring-width (TRW) chronologies spanning more than 500 years were developed in the Yellow River source area, North Eastern Qinghai-Tibetan Plateau (NE-QTP). For the two studied sites, located approximately 50 km apart, split correlation and coherence analysis reveal unstable tree-growth responses to local moisture availability. While significant correlations are obtained with April–June local precipitation, Palmer Drought Severity Index (PDSI) and river flow from 1948/1954 to 1998 and from 1948/1954 to 1970s, these correlations vanish for the time period 1970s-1998. The local instrumental climate data (precipitation, PDSI and river flow) exhibit opposite correlations with large scale modes of variability (El Niño Southern Oscillation, ENSO, and Pacific Decadal Oscillation, PDO) before and after the 1977 PDO shift. One tree-ring chronology is coherent and anti-phased with instrumental ENSO/PDO indices at 5.2-year frequency. On the longer time span, this TRW chronology is compared with PDO reconstructed from historical Chinese data. This comparison also exhibits unstable multi-decadal relationships, notably in the mid 19th century. Altogether, the comparison between our two chronologies, local instrumental climate records, and ENSO/PDO indices suggest a cautious use of local TRW records for paleoclimate reconstructions. Further studies are needed to explore both the spatial coherency of tree-ring records and the temporal stability of their response to local and large scale climate variability.