Dendroclimatological Potential of Drought-Sensitive tree Stands in Southern Tibet for the Reconstruction of Monsoonal Activity

Abstract

Southem Tibet is influenced by the Asian summer monsoon which causes 70-80% of the annual precipitation to fall between June and August, showing a steep gradient from east to west. Teleconnections between the tree-ring chronologies of a sampling network have demonstrated a distinct dendroecological region in the catchment area of the Yarlung Tsangpo river, where tree growth is mainly limited by summer precipitation. Ring width at these sites is strongly correlated to late summer (August to October) precipitation of the year prior to growth, indicating that the trees bear a high potential for the reconstruction of the rainfall variability at the northwestem fringe of the monsoonal regime. Light rings and other wood anatomical features like intra-annual growth bands can be observed in the westernmost stands of Pinus densata. If these growth bands occur in the earlywood of the tree ring, they can be explained by cold events during spring; ifthey are located in the transition zone between earlywood and latewood, they are caused by dry conditions during May and especially June, which points to a delayed arrival of the moist monsoonal air masses in southem Tibet in the corresponding years.