Characteristics Of Surface Air Temperature Change And Urbanization Effect In Urumqi

In recent years,the influence of urbanization on the temperature of the global and regional stations has been widely concerned,and Urumqi,Xinjiang,as a megalopolis in the typical arid region of Western China,has not clear understanding yet of its precise urban effect.Based on the hourly temperature data set of 28 automatic observation stations in Urumqi from 2013 to 2014 and the homogenization data of monthly and daily temperature of 6 national basic/benchmark meteorological stations in Urumqi from 1961 to 2015,the characteristics of the annual,seasonal,pentad and diurnal variations of the temperature in Urumqi were analyzed systematically,and on this basis,it refined the urban heat island effect in Urumqi.The results show that:1)The highest frequency of maximum(minimum)daily temperatures appeares in 17:00(8:00)Beijing time,with the frequency larger than 20%(30%);The appearance time of the maximum temperature in the rural is the same as that in the urban.The appearance time of the minimum temperature in the rural is the same as that in the urban except in winter.2)The maximum(minimum)value of intensity of the urban heat island usually occurs at night(day),with the maximum(minimum)value is about 1.5(0.3)? at 7:00 am(16:00 pm).For the three stages of intensity of the urban heat island:the UHII shows increase between 8 o'clock and 17 o'clock,and shows rapid increase from 17 o'clock to 22 o'clock,then stable in strong phases after 22 o'clock;The largest(lowest)value of pentad average for the UHII occurred in the 72th(67th)pentad,with the value was 1.53(0.33)?.3)Generally speaking,the strength of urban heat island was stronger in night of spring(April),and relatively weaker in summer(July).The UHII was weakest in the day time of autumn(October).The UHII was strongest in winter(January)than that in other seasons.4)From 1961 to 2015,the annual average,maximum and minimum temperature of urban and suburban area in Urumqi are increasing.The growth rate of minimum temperature in the suburbs is higher.The growth rate of average temperature and the minimum temperature of the urban are higher than it of suburbs,while the maximum temperature is lower than the suburbs.The intensity of heat islands in the average and minimum temperature are 0.08?/10a and 0.3?/10a.The urbanization contribution rates of heat islands were 26%and 47%.Howevwr,the heat island intensity of the highest temperature was negative,and the intensity was-0.02?/10a.It reveals that the main effect of urbanization in Urumqi is to affect the minimum temperature.The effect of urbanization is different with it of eastern cities in China.5)From 1961 to 2015,the growth rate of temperature in all seasons,the average temperature and minimum temperature in urban are higher than the suburbs.The growth rate of the maximum temperature is higher than the suburbs except during the summer.This shows that the highest temperature in Urumqi may be affected by the "oasis effect" in summer,what makes a "eold island" phenomenon where the city is lower than the suburbs.The analysis of seasonal heat island difference shows that the growth rate of suburban heat island intensity in winter is basically higher than that of the other three quarters.The urbanization contribution rates of the average and minimum temperature are respectively 53%and 62%,while the heat island intensity in summer is basically less than the other three seasons.The contribution rates of heat island are-100%and 54%in maximum and minimum temperature.The contri-bution of heat slands to growth of maximum temperature in winter and average temperature in summer are insufficient.6)From 1961 to 2015,the daily range of the annual and four seasons of Urumqi is declining in both the city and the suburb,this is to mean,the highest and lowest temperatures in the annual and four seasons of the Urumqi's suburb are both asymmetrical.At the same time,the suburban changes in each season are not consistent,the suburban daily range is the fastest(-0.22?/10a)in winter,the slowest(-0.04?/10a)in spring,and the most obvious decreasing trend of the daily temperature range of the urban is in autumn(-0.56OC/10a),and the slowest in spring(-0.19 ?/10a).In spring,autumn and winter,the diurnal range is significantly affected by urbanization,and summer is affected by the "oasis" effect.7)From 1961 to 2015,the UHII pentad change trend of the average temperature in Urumqi area was the fastest in the seventy-second pentad at the end of year,0.49OC/10a,and the least in the forty-sixth pentad at the end of summer which is-0.1?/10a.The highest temperature reached the maximum in the third pentad at the beginning of the year,0.44?/10a,and the lowest in the fortieth pentad at the middle of summer which is-0.09?/10a.The lowest temperature reached the maximum(0.7 ?/10a)in the fourth pentad at the beginning of year,and the minimum(0.05?/10a)in the twenty-second pentad at spring.The minimum temperature heat island intensity was all increasing in the whole 72 pentads of the year,and the average temperature heat island intensity decreased from 30 to 54 pentad,and the highest temperature was reduced from thirty-third to fifty-fourth pentad.