Annual regional precipitation variations from a 700 year tree-ring record in south Tibet, western China

Newly measured tree-ring series from 114 living and dead cypress Cupressus gigan-tea were collected from 2 high-elevation sites in the Langxian region in south Tibet, western China. Combined with 2 previous ring-width data sets from southern Tibet, the composite chronology correlated at 0.563 with instrumental precipitation over the 1961-2009 period. The low-frequency component of the chronology shows a higher correlation of 0.77 with instrumental data. We reconstructed the annual precipitation (July-June) from A. D. 1300 to 2010 for southern Tibet based on the scaling method. Wet conditions occurred in 1342-1391, 1383-1387, 1408-1423, 1453-1458, 1473-1492, 1508-1524, 1657-1667, 1701-1731, 1742-1768, 1781-1788, 1854-1868, 1917-1933, and 1994-2006, whereas dry years prevailed during 1388-1407, 1424-1452, 1459-1472, 1493-1507, 1525-1656, 1668-1700, 1732-1741, 1769-1780, 1789-1853, 1869-1916, and 1934-1993. Spatial correlation revealed that the annual precipitation reconstruction contained a strong regional precipitation signal for the southern Tibetan Plateau (TP). Coherent moisture variations on the southern TP over the past 700 yr were identified by comparison with other tree-ring-based drought reconstructions of the nearby regions. The reconstructed series showed that high (low) precipitation periods on the southern TP corresponded with dry (wet) spells on the northern TP during most of the past 500 yr, suggesting the influence of different moisture sources from the Westerlies and the south Asian summer monsoon on the northern and southern TP, respectively. The possible mechanism was related to the shift of the convergence shear line and a teleconnection of the North Atlantic Oscillation (NAO) through controlling moisture via the Westerlies.