Changes of wet and dry in the past hundred years in eastern Kyrgyzstan by tree-ring

The Western Tianshan Mountains in Kyrgyzstan,which is one of the most important water source area,is dominated by westerly and plays an important role in global change research.It is vital to understand the fact of past precipitation changes and explore its possible influence mechanism to the sustainable utilization of regional water resources. Because it is located in the arid inland area,tree rings are sensitive to moisture status and is a good proxy of past precipitation.In this paper,the tree-ring samples of Schrenk spruce(Picea schrenkiana Fisch.et Mey) were collected from the upper and lower treeline of chon-kyzyl-suu on the western Tianshan,Kyrgyzstan in 2012,were used to develop two tree-ring width chronolgies using standard dendrochronological methods.The smoothing spline(SPL),negative exponential curve(NEP) and regional curve(RCS) method were used for removing the growth trend.Finally,standard chronology(STD),residual chronology(RES) and ARSTAN chronology(ARS) were ob-tained.The similarities and differences were analyzed of tree-ring response to climate between upper and lower treeline using Climatic Research Unit(0.5° x 0.5°) and Palmer Drought Severity Index(2.5° ×2.5°).Single correlation calculation indicated that there are a best response between tree-ring width standard chronology and precipitation, and a better response between tree-ring chronology and Palmer Drought Severity Index.The correlation coefficient between KZX tree-ring width standard chronology(SPL) and precipitation from previous July to current June in eastern Kyrgyzstan was 0.61(p 0.000 001).The precipitation and Palmer Drought Severity Index that from previous July to current June over past hundred year were reconstructed using tree ring width chronologies.The model passed all the calibration by the leave-one-out cross-validation method.The power spectrum analysis and morlet wavelet transform reveals that wet and dry spells change with the quasi-periodic 6 a,13 a and 21 a in eastern Kyrgyzstan over the past hundred years.The oscillations were more strong from 1880s to 1920s,the periodic oscillation was significantly reduced in late 20th century,especially after 1980,and change cycles of 13 a and 21 a were most obvious in 1920-1980.The cycles implies that wet and dry changes in the past century in eastern Kyrgyzstan not only contain the local information,but also were impacted by a wider climate change,and the global climate change was further proved.The sliding T-test shows that there were 4 abrupt changes in 1913,1943,1972 and 1950.The dry and wet changes were consistent between the eastern Kyrgyzstan and the Tianshan Mountain in China over the past hundred years:It was dry in 1890s,wettest in 1900s,driest decade in 1910s,driest year in 1917,then the precipitation increased from 1920s to 1930s,dry in 1940s,wet from 1950s to 1960s,dry in 1970s,and wet from 1980s to 2000s,especially from 1980 to the present,which was the longest wet period for the past 100 years.Reconstruction sequence could better reflect the wet and dry change in most areas of the Western Tianshan Mountains,especially on the northern slope of the Tianshan Mountains in Kyrgyzstan.