青藏高原近地表土壤冻融状况的时空变化特征

Spatial-temporal Changes of the Near-surface Soil Freeze-thaw Status over the Qinghai-Tibetan Plateau

利用青藏高原(下称高原)87个气象台站的日最低地表温度和气温资料,通过线性回归和相关分析法,分析高原1980-2015年近地表土壤冻融状况变化趋势及其与气温、海拔和纬度的相关性。利用M ann-Kendall检验对其进行突变分析,并探讨其空间变化特征。结果表明:近36年,高原近地表土壤冻融状况发生显著变化。冻结起始时间推迟约26天,其变化速率为0.72 d·a^(-1),冻结结束时间提前约14天,速率为0.40 d·a^(-1);冻结持续时间和冻结天数分别缩短约41天和33天,其变化速率分别为1.13 d·a^(-1)和0.93 d·a^(-1)。高原冻融状况变化整体表现一致,局部地区略有差异。高原中东部地区冻结起始时间较早,结束时间较晚;而在东南部地区则存在相反的变化特征,这是由于该地区海拔较低,且全年土壤温度较高导致。就冻融状况变化速率而言,东部地区变化最快,西部适中,变化较慢的站点零星分布在中部和南部地区。气温对近地表土壤冻融状况有重要影响,但气温对土壤冻融循环存在一定的滞后作用。此外,高原近地表土壤冻融状况与海拔呈极显著相关,随海拔的降低,冻结起始推迟,冻结结束时间提前,冻结持续时间和冻结天数显著减少。

Based on the surface soil daily minimum temperature and air temperature datas from 87 meteorological stations over the Qinghai-Tibetan Plateau （ QTP）, the trends of the near-surface freeze-thaw status and its corre- lation with air temperature, altitude and latitude was analyzed by using the linear regression method and correla- tion method. Using Mann-Kendall method to test the abrupt change and discuss the spatial variation characteristics of the near-surface soil freeze-thaw status over QTP. The results show that the near-surface soil freeze-thaw status changed significantly on QTP in recent 36 years. The first date of the near-surface freeze was delayed by about 26 days, or at a rate of 0.72 d ~ a-1, and the late date of the near-surface freeze was advanced by about 14 days, or at a rate of 0. 40 d ~ a-~. The number of duration days and freeze days of the near-surface freeze decreased about 41 and 33 days respectively, and the rate of change was 1. 13 d ~ a-1 and 0.93 d ~ a-1 , respectively. The trend of the near-surface soil freeze-thaw status was same overall QTP, while in some areas was slight differences. The central and eastern region of QTP, the first date of the near-surface freeze was earlier and the last date was later than other regions. However, there was a contrary variation in the southeast region. It may be the lower elevation of the stations and it had the higher air temperature all years. For the change rate of the near-surface soil freeze- thaw status, the eastern part of QTP changed the fastest, the western was moderate and the stations that changed slower scattered in central and southern regions. The temperature had a significant effect on the near-surface soil freeze-thaw status, but air temperature had a certain lag effect on soil freeze-thaw cycle. And the near-surface soil freeze-thaw status was great significantly correlated with altitude. With decreasing elevation, the first days of the near-surface soil freeze was delayed and the late days was advanced, and the numbers of duration days and freeze days of the near-surface soil freeze were significantly decreased.