Drought fluctuations based on dendrochronology since 1786 for the Lenglongling Mountains at the northwestern fringe of the East Asian summer monsoon region

The Lenglongling Mountains (LLM) located in northeastern part of the Tibet Plateau, belong to a marginal area of the East Asian summer monsoon (EASM) and are sensitive to monsoon dynamics. Two tree-ring width chronologies developed from six sites of Picea crassifolia in the LLM were employed to study the regional drought variability. Correlation and temporal correlation analyses showed that relationships between the two chronologies and self-calibrated Palmer Drought Severity Index (sc_PDSI) were significant and stable across time, demonstrating the strength of sc_PDSI in modeling drought conditions in this region. Based on the relationships, the mean sc_PDSI was reconstructed for the period from 1786 to 2013. Dry conditions prevailed during 1817–1819, 1829–1831, 1928–1931 and 1999–2001. Relatively wet periods were identified for 1792–1795 and 1954–1956. Spatial correlations with other fourteen precipitation/drought reconstructed series in previous studies revealed that in arid regions of Northwest China, long-term variability of moisture conditions was synchronous before the 1950s at a decadal scale (1791–1954). In northwestern margin of the EASM, most of all selected reconstructions had better consistency in low-frequency variation, especially during dry periods, indicating similar regional moisture variations and analogous modes of climate forcing on tree growth in the region.