河西走廊近40年地表土壤冻融状态变化特征

Analysis of Spatiotemporal Variations of Freeze-thaw State of Surface Soil in Hexi Corridor in Recent 40 Years

为探究河西走廊地区土壤冻融规律,基于ERA5-LAND逐小时地表温度数据,通过划分不同冻融阶段并结合Mann-Kendall趋势检验及线性回归法,分析河西走廊近40年地表土壤冻融状态变化特征。结果表明:(1)春季过渡期发生天数呈现平原多山区少,总体年均发生天数为65天以上,完全融化期发生天数整体上为北部多于南部,在同一纬度上呈东部多于西部,且发生天数为200天以上的地区不断增加;秋季过渡期年均发生天数最少,为50天左右,完全冻结期发生天数随海拔升高而增加,其中春季过渡期发生天数的空间分布随时间变化较明显。(2)春季过渡期和完全融化期起始日期由北向南逐渐推迟,南北差异最大为90天以上,且不同时期完全融化期起始日期空间分布变化明显。秋季过渡期起始日期与前者相反,由北向南逐渐提前,不同时期空间分布无明显差异。绝大部分地区在12月份进入完全冻结期,高海拔山区在11月份进入完全冻结期。(3)研究区大部分地区春季过渡期起始日期滞后,完全融化期起始日期提前,故春季过渡期发生天数总体以0.2天/年的速率减少,而大部分地区秋季过渡期起始日期滞后,致使完全融化期发生天数以0.3天/年的速率增加。研究区北部完全冻结期发生天数呈增加趋势,而南部祁连山脉一带则呈现减少趋势,完全冻结期起始日期总体以0.03天/年的速率推迟。(4)山地、绿洲和荒漠地区近40年完全融化期发生天数分别以0.393,0.321,0.288天/年的速率增加,起始日期分别以0.134,0.188,0.206天/年的速率提前,完全冻结期发生天数分别以0.353,0.219,0.016天/年的速率减少,起始日期以0.06,0.10,0.01天/年的速率推迟。在全球变暖趋势下,年均气温每升高1℃,完全融化期发生天数增加8.1天,起始日期提前4.53天,完全冻结期发生天数减少9.02天,起始日期推迟3.27天。研究结果可为土壤冻融对气候变化响应相关研究提供理论依据。

In order to explore the law of soil freeze-thaw in Hexi Corridor,based on the hourly surface temperature data of ERA5-LAND,the changes of surface soil freeze-thaw state in the past 40 years were analyzed by dividing different freeze-thaw stages and combining Mann-Kendall trend test and linear regression method.The results showed that:(1)The number of occurrence days in the spring transition period were more in plains than in mountainous areas,and the average annual occurrence days were more than 65 days.The number of occurrence days of complete melting period was more in the north than in the south,more in the east than in the west at the same latitude,and the number of occurrence days in more than 200 days was increasing.The number of average annual occurrence days in the autumn transition period was the least,about 50 days,and the number of days of complete freezing increased with the increase of altitude,among which the spatial distribution of the number of days in the spring transition period changed significantly with time.(2)The start date of the spring transition period and the complete melting period was gradually postponed from north to south,and the maximum difference between the north and the south was more than 90 days,and the spatial distribution of the start date of the complete melting period in different periods changed significantly.The start date of the autumn transition period was the opposite of the former,gradually advancing from north to south,and there was no obvious difference in spatial distribution between different periods.Most areas were completely frozen in December,and high-altitude mountainous areas were fully frozen in November.(3)The start date of the spring transition period was lagging behind in most areas of the study area,and the start date of the complete melting period was advanced,so the number of days of the spring transition period decreased at a rate of 0.2 d/a,while the start date of the autumn transition period in most areas was lagging,resulting in the increase of the number of days of complete melting period at a rate of 0.3 d/a.The number of days of complete freezing period in the northern part of the study area increased,while the southern Qilian Mountains showed a decreasing trend,and the start date of the complete freezing period was generally delayed at a rate of 0.03 d/a.(4)The number of days of complete melting in mountainous areas,oases and desert areas in the past 40 years increased at the rates of 0.393,0.321 and 0.288 d/a,the start date was advanced by 0.134,0.188 and 0.206 d/a,the number of days of complete freezing period decreased by 0.353,0.219,and 0.016 d/a,respectively,and the start date was delayed at the rate of 0.06,0.1,0.01 d/a.Under the trend of global warming,for every 1°C increase in annual average temperature,the number of days of complete melting increased by 8.1 days,the start date was advanced by 4.53 days,the number of days of complete freezing period decreased by 9.02 days,and the start date was delayed by 3.27 days.The results can provide a theoretical basis for the study of soil freeze-thaw response to climate change.