May-June drought reconstruction over the past 821 years on the south-central Tibetan Plateau derived from tree-ring width series

Knowledge of drought variability and their possible mechanisms during the past hundred years is still limited in the mountainous region of south-central Tibetan Plateau (TP). In this study, a long-term tree-ring width chronology dating back to 1190 CE was combined using 328 increment cores from the Nagqu region. Based on the relationships between this tree-ring width chronology and climate data, we reconstructed May-June self-calibrated Palmer Drought Severity Index (scPDSI) for the past 821 years (1190-2010 CE). Additional comparisons with other available precipitation or drought reconstructions were conducted. We further investigated the influence of the South Asian summer monsoon (SASM) on the drought variability in our study region. Results indicated that our tree-ring width chronology contained stable drought signal in the early summer season (May-June). During the past 821 years, the longest dry and wet periods lasted for 116 and 90 years, respectively, based on a 21-year Fast Fourier transform filter. Specifically, longer than ten years' dry periods prevailed during 1211-1245 CE, 1280-1358, 1421-1471, 1500-1571, 1580-1598, 1650-1691, 1782-1807 and 1867-1982; while wet intervals occurred in 1190-1210 CE, 1246-1279, 1359-1420, 1472-1499, 1599-1649, 1692-1781, 1808-1866 and 1983-2010. Generally consistent dry and wet intervals across the southern TP were found by comparisons with other available datasets during their common periods. Interestingly, we detected an unstable influence of the SASM on the May-June drought variability in our study region, at least for the past three and a half centuries. This study therefore gives a new perspective of drought variability as well as their relationships with the SASM over a long-term period on the south-central TP.