An analysis of precipitation variations in the west-central Tianshan Mountains over the last 300Â years

Tree-ring based precipitation/PDSI series from six sites were applied to reconstruct the regional precipitation (dry/wet) index for the west-central Tianshan Mountains for the last 300 years. The analysis of the reconstructed index series indicates that the dry and wet years in the whole time period were almost equal in frequencies. The results show that the 300-year period is characterized by a series of dry/wet stages, including six dry stages (1707-1719, 1768-1782, 1822-1832, 1880-1886, 1913-1924 and 1973-1989) and five wet stages (1723-1741, 1843-1857, 1893-1907, 1933-1940 and after-1990 period). The reconstructed regional precipitation (dry/wet) series also exhibits quasi-periodicities of 2-5 y, 7-8 y, 11 y, 30 y, 50 y and 80 y, with the 11 y, 30 y and 50 y quasi-periodicities being more significant. Shifts from dry to wet climate occurred in 1720, 1779 and 1886, and the shifts from wet to dry climate occurred in 1741, 1854 and 1904. In addition, the analysis also indicates that solar activities might have significantly affected the regional precipitation (dry/wet) variability on ∼10 y scale during 1770s-2000s. The effects of solar activities on annual precipitation in the Tianshan Mountains are more complicated than expected, and the complexity might be associated with a number of unknown processes.