THE HISTORICAL RECONSTRUCTION OF THE MAXIMUM TEMPERATURE OVER THE PAST 195 YEARS, LINXIA REGION, GANSU PROVINCE BASED ON THE DATA FROM Picea purpurea Mast
Global warming was widely accepted in the 20th century, but there were diversities in different region. This paper analyzed the background of the regional response to global change in the Linxia region of the west of the Loess Plateau by tree ring. Sampling points is located in the Songmingyan National Forest Park in Linxia City, Gansu Province, and it belongs to the northern piedmont of Linxia Taizi Mountain (35. 24°N, 103. 40°E). According to the growth conditions of the trees, 39 tree cores from 21 different trees were collected, and recorded as SMY. This sampling point's altitude is from 2551m to 2638m, which is located below the Picea purpurea's tree line. Based on the tree ring width analysis of Picea purpurea Mast. in Linxia region, Gansu Province, we found that tree-ring width chronologies had a low correlation with precipitation and PDSI, but had the highest correlation with 3 ~10 monthly mean maximum temperature (r = 0. 578, p < 0. 0001, n = 62) in this study, which the meteorological data was from Linxia Meteorological Station (35°35'N, 103oll'E; a. s. 1. = 1918.5m,1951 ~ 2012A.D.). Based upon the correlation analysis, the mean maximum temperature from March to October was reconstructed using STD chronology. The transfer function saw text. We reconstructed the mean maximum temperature from March to October of 1818 ~ 2011 A.D. using tree-ring width index in study region. The explained variance reached 40%,and 38% after adjusting degree of the freedom. The reconstruction displayed the fluctuation of temperature in this region. The years of high temperature and low temperature in reconstruction sequence are roughly same, respectively 14. 9% and 12. 9%. After an 11 -year moving average, the reconstruction showed that cold and warm intervals appear alternatively in decadal scale. This presents four warm periods (1818 ~1854A.D.,1882 ~1900A.D.,1937 ~ 1966A.D. and 2001 ~2012A.D.),with temperatures lower than the mean ; and three cold periods (1855 ~ 1881 A.D.,1901 ~ 1936A.D., and 1967 ~ 2000A.D.),with temperatures higher than the mean. Moreover, the reconstruction temperature curve didn't show a significant warming trend at the early stage over the past 195 years, but a significant warming trend in the late 20th century, and it was up to 0. 77℃ from 1970 ~ 1980A.D. mean maximum temperature to 2001 ~ 2012A.D. mean maximum temperature, which matched well with the IPCC Fifth Report. This showed that Linxia region responded to this global warming event. Spatial analysis showed that 3 ~10 monthly mean temperature change has a certain spatial representation in Linxia region, which could stand for the variation of temperature on the central west of Loess Plateau. MTM analysis showed remarkable 42. 74,7. 79~3. 18 and 2. 77 year cycles at a 95% confidence level for the past 195 years. The cycle of 42. 74 years is similar to the Bruckner cycle, and it matches well with the cycle of PDO. It is also possibly associated with variations of solar activity. The cycles of 3 ~ 7 years correspond to the cycles of Asian ENSO,which was reported other paper on a number of occasions. The cycle of 2. 77 years is associated with either ENSO or TBO. Above all, the maximum temperature is influenced by not only the regional climate, but also variations of solar activity, ENSO and TBO in this study.