TREE-RING RECONSTRUCTIONOF HYDROTHERMIC INDEX (AD 1680-2005) IN ISSIK-KUL REGION (TIEN-SHAN, KIRGIZSTAN REPUBLIC)
New regional ring width chronology of spruce (Picea Schrenkiana Fish. et May.) for the period 1680-2005 includes samples collected at the lower treeline in the Issik-Kul lake region (Tien- Shan, Kirgizstan). As the age of the trees at the lower treeline is not very long and rarely exceeds 100 years, we used the wood from old buildings (late 19th-early 20th century) to extend the chronology. The low precipitation and high temperature during the warm season limit the growth at the lower treeline; this allows the reconstruction of the hydrothermal index for the last 324 years. The best fit model includes the June-September precipitation of the previous and current years divided by the average temperature of the same period. The reconstruction accounts for 41 % of the variance in the observed hydrothermal index over 1896-1988. However, the correlation between the reconstructed and observed hydrothermal index has decreased after the 1960s, although it is still statistically significant. A possible cause of this decrease is the increase in summer temperature and in the length of the growing season that occurred in the Tien-Shan Mountains in the1960s-1970s and, consequently, a change of the response factor. According to this reconstruction, the droughts in the Issik-Kul Region occurred in 1742-43, 1774-75, 1828-29, 1856-57, 1873-74, 1879-80,1884-85, including those during the instrumental period in 1894-95 and 1916-17. The longest droughts occurred in 1768-69 /1774-75 and1741-42/1748-49. In general, the 19th century in the Issik-Kul Region was drier than the 20th century. The 20th century does not look un-usual in terms of drought occurrence.