APRIL TO JULY PRECIPITATION RECONSTRUCTION BASED ON TREE-RING WIDTH FOR THE PAST 242 YEARS IN THE NORTHERN GREATER KHINGAN MOUNTAINS,NORTHEAST CHINA
The northern region of the Greater Khingan Mountains is one of the sensitive areas affected by climate change,and due to the relatively short-term measurement data,there is still a weak understanding of interannual and interdecadal regional precipitation variability.To evaluate the strength and frequency of similar events,and our understanding of historical climatic regimes of Northeastern China,it is important to obtain a longer record of past climatic variations.Tree-ring cores of Pinus sylvestris were collected in the Mangui Town in Hulunbuir City,Inner Mongolia Autonomous Region(52°04′N,122° 11′E;710 m).The forest resources in the Mangui Forest Area are rich and widely distributed,and tree species mainly include Larix gmelini,Betula platyphylla,Populus davidiana,and Pinus sylvestris.The forest soil is mostly brown coniferous soil with a small amount of dark meadow soil and swamp soil,and the soil layer thickness is about 30cm.A total of 55 core tree rings of Pinus sylvestris were collected using an increment borer and a tree ring width chronology was established.Cores were brought to the laboratory and air-dried prior to mounting and sanding;all samples were prepared following standard dendrochronological techniques.Tree-ring widths were measured to 0.01mm using a LINTAB 1M 6.0 measuring system.The width measurement and cross-dating accuracies were verified using COFECHA.Correlation analysis showed that the precipitation in spring and early growth season was the main limiting factor for the radial growth of Pinus sylvestris var.mongolica in Mangui area.The radial growth of trees had the highest correlation with the precipitation(r=0.549,p＜0.001)from April to July in the current year.A single linear regression model was used to reconstruct the precipitation from April to July of the current year in this area for the past 242 years.The reconstruction equation explained 30.1％of the variance of the precipitation.The equation successfully passed the leave-one-out methods,which indicated that the reconstructed sequence results were stable and reliable.In the past 242 years(1776～2017,EPS＞0.85),there were five wet periods(1 788～1805,1841～1871,1887～1 899,1926～1966 and 1993～2000)and six dry periods(1776～1787,1806～1840,1872～1886.1900～1925,1967～1992 and 2001～2017).1900～1925 was the worst drought in the study area in the past 242 years.The dry and wet periods of reconstructed precipitation were in good agreement with the results of other comparison series.Spatial correlation analyses with a gridded precipitation dataset showed that our precipitation reconstruction sequences had a good representation for the variation of April-July precipitation in northern Greater Khingan Range.In addition,the spatial analysis with SST data also showed that the precipitation reconstruction sequences from this study were significantly positively correlated with SST in the Pacific Ocean.Power spectrum and wavelet analysis showed that the reconstruction sequence had significant periods of 2.1,2.5,2.8,4.1,7.0 and 63.7 years(p＜0.01).In summary,the change of precipitation from April to July in the study area can be related to some large-scale climate oscillations,such as El Nino-Southern Oscillation and Pacific Decadal Oscillation.
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