Variation Tr ends of the Freezing and Thawing Index along the Qinghai-Xizang Railway for the Per iod 1966-2004
青藏铁路沿线1966-2004 年 冻结与融化指数的变化趋势

Yearly freezing and thawing index for seven main stations along the Qinghai-Xizang Railway were calculated based on daily maximum and minimum temperature records for the period 1966-2004. Statistical characteristics and variations of the annual freezing and thawing index for these stations were outlined. Trends in annual freezing and thawing index for these stations were analyzed using two methods,namely a non-parametric trend test method,i.e. the Mann-Kendall test and a simple linear regression method. The results show that the mean annual freezing index for these stations ranges from 95 to 2300 oC,and the mean annual thawing index ranges from 630 to 3250 oC. The mean annual freezing index of the seven stations exhibited decreasing trends with linear tendencies ranging from -16.6 to -59.1 oC/10a,and the mean annual thawing index of the seven stations showed increasing trends with linear tendencies ranging from 19.83 to 45.6 oC/10a. The results of the MK trend test show that the significant decreasing trends in the annual freezing index for most stations except for Golmud were detected at the 0.05 significant level. The increasing trends in the annual thawing index for four stations except Golmud and Tuotuohe were determined by the MK method at the 0.05 significant level. Golmud was the only station where no significant trends in both the annual freezing and thawing index were found. Results from the simply linear regression method are similar with that from the MK test.