Analysis Of Climate Changes In Semi-humid And Arid Regions Of Northwest China

Basing on the data of temperature,precipitation,extreme temperature time from 1955 to 2015,and the data of Evaporation from 1978 to 2001 in Xi'an and Urumqi,this paper studies the characteristics of climate change in the two areas by using the linear trend estimation,sliding average,Mann-Kendall test,Morlet wavelet analysis.The results are as follows.(1)Overall,the temperature in both Xi'an and Urumqi in the past 61 years experiences a warming trend,and the increasing rate of temperature in Xi'an is larger than that in Urumqi.The linear trend of annual average temperature in Xi'an is 0.386 ? / 10 a while that in Urumqi is 0.284 ? / 10 a.The average temperature of the four seasons in Xi'an shows a warming trend,with the main oscillation period of 8a 20 a,28a and 40 a.The average temperature of the four seasons in Urumqi all shows a warming trend except that in summer,with the main oscillation period of 35 a,35a,35 a,and 33 a.(2)The extreme maximum temperatures of all seasons in Xi'an all keep an increasing trend,but there is no obvious mutation in these years.The main oscillation periods of extreme maximum temperature in four seasons of long time series are 12 a,39a,23 a and 14 a respectively.The extreme maximum temperature in the four seasons in Urumqi shows a trend of decreasing in spring,summer and autumn,but it is not striking,and no obvious year of mutation is found.The main oscillation periods of long time series are 27 a,38a,32 a,10a.(3)There is a trend of getting warmer in the extreme minimum temperature of the four seasons in the two regions.Summer warming in Xi'an is prominent,and the mutation of the extreme minimum temperature in the four seasons were respectively in 1996,1994,2000 and 1990,the main oscillation periods of long time series of which were respectively 31 a,16a,23 a and 12 a.The spring temperature in Urumqi apparently increased,and the mutation in spring took place in 1995,whereasthe temperature in summer almost stays steady and no mutation occurs.Meanwhile,the mutation in autumn was mainly in the late 1990 s while the mutation in winter was in the late 1970 s.The main oscillation periods of long time series are respectively 9a,34 a,9a,10 a.(4)The annual precipitation in Xi'an in recent 61 years shows a decreasing trend,while Urumqi experiences an increasing trend.The precipitation in Xi'an in the past 61 years declines mildly,and the oscillation periods of long time series were respectively 22 a,8a and 4a.The precipitation in the four seasons in Xi'an had a downward trend.But it was generally not very sharp except that the spring precipitation had a mutation.The main oscillation periods of the four-season precipitation are 24 a,24a,10 a and 15 a respectively.The precipitation in Urumqi increased obviously over the past 61 years.The oscillation periods of annual precipitation of long time series were 17 a,14a and 4a respectively.The precipitation in four seasons in Urumqi increases The increasing trend of precipitation in winter is obvious while the other seasons arenot.The precipitation in winter obviously changed in 1993.The main oscillation periods of four season's precipitation of long time series are 2a,49 a,31a,5a.(5)The annual and seasonal variation characteristics of precipitation days.In the past 61 years,the annual precipitation days in Xi'an and Urumqi showa downward trend,and the rate of decline in Xi'an is greater than that in Urumqi.The precipitation days of four seasons in Xi'an decreased obviously except in summer.Other than the summer,the mutation of precipitation days of the other 3 seasons took place in 1993,1969 and 1976 respectively.The main oscillation periods of four season's precipitation days of long time series are 24 a,25a,19 a and 16 a.The precipitation days in Urumqi have a downward trend in spring,summer and autumn,but this downward trend is not obvious and there is no obvious year of mutation.The main oscillation periods of four season's precipitation days of long time series are 36 a,34a,3a,24 a.(6)Characteristics of climatic continentality and dryness change.The continentality of Xi'an and Urumqi both showed a decline first and then a slight increase.This is due to the fact that the warming rate in the inland areas of northwestern China in winter is significantly greater than that in summer,thus reducing its continentality.Xi'an's dryness tends to increase,while Urumqi's dryness tends to decline.The climate warming and the decrease of continentality in Xi'an and Urumqi,and the decrease of dryness in Urumqi are all beneficial to the improvement of the fragile ecological environment in the northwest region.However,Xi'an's dryness is on the rise and it is harmful to the ecological environment in the water-deficient northwestern region.