Causes And Effects Of Spatial And Temporal Variations Of Extreme Low Temperature In Heihe River Basin During 1961-2015

Over the past century,global warming leads to an increased in the frequency and intensity of extreme weather events,which has had a more profound impact on the ecological environment and human social and economic development.Compared with the average state,extreme events have more emergency and unpredictability,which have the most direct impact on the ecological environment,human health and social economic development,so it has been gained comprehensive attention of scholars.Compared with extreme high temperature event,the change of extreme low temperature event becomes more acute.Heihe river basin is the second largest inward flowing river in northwest inland basin,the natural landscape is complete and it is through the mountain-oasis-desert oasis,respectively.And the air temperature changes greatly.How are the change of extreme low temperature and influence mechanism? The research shows very important.Based on temperature data 52 grid points from 1961 to 2015 in the heihe river basin,selecting cold days(TX10),cold night(TN10),ice days(ID),frost days(FD),monthly minimum value of daily minimum temperature(TNn),monthly maximum value of daily minimum temperature(TNx),cold spell duration days(CSDI),cold period(CP),and using linear regression analysis,spatial interpolation,correlation analysis,Morlet wavelet power.We analyze spatial and temporal characteristics and their causes for extreme low temperature in Heihe River basin.The main conclusions of this paper are as follows:(1)The occurrences of TX10,TN10,ID,FD and CSDI have significantly decreased by-2.21d/10 a,-4.4d/10 a,-2.37d/10 a,-3.73d/10 a and-0.45d/10 a,respectively.TNn and TNx have significantly rised by 0.54?/10 a and 0.36?/10 a,respectively.CP shows statistically significant shortening trend at rate of-0.5p/10 a.The inter-decadal changes show that TX10 and TN10 have remarkable changes in the1980 s,others have Significant changes in the 1990 s.(2)Obvious spatial difference can be found for extreme low temperature in Heihe River basin.From Heihe river basin upstream to downstream,TN10 shows a increasing trend,ID and FD have significantly decreased trend,TNn and TNx have arising trend,CP has a shorting trend;TX10 and CSDI is the longest in the middle Heihe River Basin.(3)Mutation test showed: Mutation points of TX10 and TN10 are earlier in the1970 s,other indices have mutations in the 1980s-1990 s.Extreme low temperature of Heihe River basin have a 2~4years,2~7years short cycle,which is related to the Atmospheric circulation and El Nino events,others also exist a 11 years and 22 years cycle,which is related to solar activity.(4)With the increase of altitude,TX10 and TN10 have a gradually decreasing trends at rates of-0.004d/100 m and-0.003d/100m;ID and FD have a gradually increasing trends at rates of 2.574d/100 m and 4.338d/100m;TNn and TNx have a gradually decreasing trends at rates of-0.349?/100 m and-0.408?/100m;CSDI has a gradually decreasing trends at rates of-0.018d/100m;CP shows statistically significant extending trend at rate of 0.66p/100 m.(5)the correlation of extreme low temperature in Heihe river basin and average temperature is better,extreme low temperature shows clear responses to regional warming,and regional warming has different effects on the extreme low temperature.(6)The narrowing of the northern hemisphere polar vortex area(NHPVAI)and Asia polar vortex area(APVAI)are a possible cause that lead to changes of extreme low temperature in heihe river basin;El Nino and southern oscillation have a certain effect for extreme low temperature in Heihe River basin;carbon dioxide emissions(CDE)caused by Human activity can not be ignored for the influence of extreme low temperature of the heihe river basin.