RESUMO
We constructed standard tree-ring-width chronology of Picea likiangensis var. rubescens for the Larima sampling site in the Ganzi Prefecture, Sichuan Province, by the single-free detren-ding method. The results showed that there was significant and positive correlation between the tree-ring chronology and March-August 1-month scale standardized precipitation and evapotranspiration index (SPEI1) of Yajiang region. The variation of the March-August SPEI1 sequence for 1942-2008 was reconstructed based on the current and last year sequences of the tree-ring chronology, with an explained variation of 42.8%. The newly reconstructed series mainly represented the variation of SPEI1 in the low-frequency domain over the historical period. Three wet periods were found in 1442-1465, 1516-1601 and 1836-2008, while the two intervals were dry periods for the March-August SPEI1 reconstruction in the Yajiang region of West Sichuan Plateau. There was a significant drying trend in 1456-1762 for the reconstructed sequence, a significant wetting trend in 1455-1762, while the wetting trend was the most significant in 1959-2008. Mutation test showed that the sudden changes from dry to wet for the March-August SPEI1 reconstructions occurred in 1512, 1733, 1767, 1831, 1941, 1957 and 1975, while that in 1684 and 1961 was the opposite. The comparison with surrounding region showed a good coherence of variations in the low-frequency domain among the SPEI1 reconstruction for the Yajiang region, the annual precipitation reconstruction for the northeastern Tibetan Plateau, and the SPEI05 reconstruction for the northern slope of the eastern Qilian Mountains. The reconstructed sequence well represented the variation of the March-August SPEI1 in the northeastern Tibetan Plateau and the southern Qinhai Province.
