| Global warming has become an indisputable fact.In the past 100 years,the global average temperature has increased by about 0.6±0.2?,and the earth's cryosphere is changing rapidly.Permafrost is an important part of the earth's cryosphere,and its degradation rate is faster than expected.Permafrost has an important impact on people's life and economic environment in cold regions.Mohe city is a typical city in permafrost region in China.The permafrost in Mohe city has degraded rapidly under the comprehensive influence of complex factors such as global warming and urban heat island effect.According to the data of Mohe meteorological station and MODIS surface temperature,the air temperature and surface temperature in Mohe increased from 2001 to 2019,and the ground air temperature difference increased at the rate of 0.23?/a.In the frozen soil exploration of Mohe City,researchers found that there is no frozen soil layer in the detection range of 0-10 m in the urban area,and the frozen soil is seriously degraded;The ground temperature of permafrost in the suburbs is low,the frozen soil layer is thick,the upper limit of frozen soil is shallow,about 1.5-3.0m,and the thermal state of frozen soil is relatively stable.This shows that the urban heat island effect has a strong impact on permafrost,and the urban heat island effect in permafrost area is an important factor affecting the state of urban permafrost.This paper selects 14 periods of remote sensing image data in the summer from 2000 to June,July and August 2020,the daily MODIS surface temperature product mod11a1 data in 2013,2016 and 2020,and the daily minimum surface temperature data of 0cm soil temperature in Mohe meteorological station from July 1,1999 to June 30,2020.Through the analysis of the temporal and spatial variation distribution characteristics of urban heat island in Mohe City,the long-term temporal variation of surface soil freezing time The correlation analysis between heat island intensity index and surface soil freezing period and freezing days,and the spatial analysis between urban heat island intensity and surface soil freezing days,try to reveal the impact of urban heat island effect on surface soil freezing in permafrost area.The main conclusions are as follows:(1)From 2000 to 2020,the sum of heat island area and strong heat island area in Mohe city decreased from 3.63% in 2000 to 2.47% in 2020,with a small change range;From 2000 to 2020,the area of strong green island in Mohe city increased first and then decreased,and the area remained basically unchanged;The distribution of heat island intensity in Mohe city is mainly in the middle area and green island area,and the sum of the areas of the middle area and green island area in each year exceeds 80%;From 2000 to 2020,the change of heat island intensity area in Mohe city is mainly from green island area to middle area.The area of green island area decreases from 44.30% in 2000 to 24.24% in 2020,and the area of middle area increases from 51.39% in 2000 to72.72% in 2020.There is no significant change in the intensity proportion of urban heat island in Mohe city from 2000 to 2020.(2)From 2000 to 2020,the start time of surface soil freezing in Mohe city was delayed by about 11 days,and the linear slope was about 0.557 days / year;The end time of surface soil freezing is about 13 days earlier,and the linear slope is about-0.655 days / year;The freezing period of surface soil is reduced by about 24 days,and the linear slope is about-1.224 days / year;The freezing days of surface soil are reduced by about 17 days,and the linear slope is about-0.885 days / year;There is an obvious nonlinear relationship between the freezing days and the freezing period of surface soil in Mohe city.The longer the freezing period is,the more the actual freezing days are.(3)From 2000 to 2020,the urban heat island intensity index of Mohe city decreased by about 3.6?,and the linear slope was about 0.183?/A;The correlation analysis between heat island intensity index and surface soil freezing period and freezing days in Mohe city shows that the heat island intensity index is reduced by 1?,the freezing period is shortened by 5.183 days,and the freezing days are reduced by2.492 days.In Mohe City,which is located in the permafrost area,the urban heat island effect has a certain impact on the surface soil freezing,and the surface soil freezing period and freezing days will be shortened.(4)Through the spatial analysis of the heat island intensity classification map and the spatial distribution map of surface soil freezing days in Mohe city in 2013,2016 and2020,it is found that the surface soil freezing days corresponding to the urban heat island area of Mohe city are less,and the surface soil freezing days corresponding to the Green Island area in the northern and southern suburbs are more,which has a strong spatial correlation.There is a negative correlation between the intensity of urban heat island and the freezing days of surface soil,that is,the stronger the intensity of urban heat island,the less the freezing days of surface soil. |
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