| Chinese urbanization is pacing rapidly,the scale of cities has been greatly expanded,and regional urban circle(clusters)have gradually developed.Urbanization has changed the type and structure of the city's underlying surface.Particularly the impervious and hardened road surface has increased enormously.The natural ecology such as vegetation,forests,water,marshes have been severely wrecked.And,the local thermal and water circulation have undergone major changes.The density of reinforced concrete buildings(structures)has rose steeply,so do the average canopy height the roughness,which have changed the normal direction of the airflow and increased the frequency of calm winds.Human activities and emissions from industrial production have changed the local thermal conditions and increased atmospheric particulates and aerosols over the city.The effects of urbanization,especially large-scale urban agglomeration effects,has led to abnormal changes in the local climate,appeared with the effects of urban "heat island,rain island,dry island,calm wind island,and turbid island",and an increased frequency of high-temperature heat waves,internal haze,haze,etc,which had bad influence on the normal operation of the city and the people's life.The climate change of the urban circle(clusters)is an indisputable fact.Due to the influence of human activities and over-exploitation,the climate changes of the urban circle(clusters)is more complex and changeable.On the one hand,the city circle(clusters)is in the global atmosphere,therefore it is also affected by global climate change and it is called the effect of changes in the climate system.On the other hand,local climate change caused by human activities and over-exploitation,and it is also called the impact of urbanization on climate change.How to separate the climate change of urban circles(groups)brought by urbanization is a technology that both concerned at home and abroad.The suburbs or villages on the edge of the urban circle which are far away from the urban areas and less affected by the local climate change brought by urbanization.Generally only affected by the changes of the global climate system,therefore,they can be used as a contrast station of urbanization climate effects.In this paper,taking the Wuhan city clusters for an example.The urban circles and villages were identified according to the data of urban population,land cover and nighttime lighting.And also the typical urban stations and comparison rural stations were selected.The UMR(Urban Minus Rural)method was used to analyze the differences in the changing trends of air temperature,precipitation,relative humidity and wind speed in urban and rural areas according to the data of these elements from 1960 to 2016 which were homogenized.And calculate the influence value and contribution rate of urbanization to those above elements.And also the spatial distribution of the trend was analyzed.The comprehensive index of urbanization was figured out by the analysis on principal components.And then the regression modeling was undertook with each meteorological element to reveal the relationship between urbanization and regional climate changes.The main conclusions are shown as follows:(1)Influence of urbanization on temperature changesThe characteristics of time change.Urbanization has the greatest impact on temperature changes,showing a significant warming effect,which is the main reason for the urban heat island effect.Urbanization has a warming effect on the annual average temperature,maximum and minimum temperature of urban stations.The corresponding urbanization warming rates,which was obtained by UMR analysis,were 0.22?/10a,0.05?/10a,and 0.35?/10a respectively,and the contribution rates of urbanization warming were 62.87%,23.77%,and 70.68%.Urbanization has a warming effect on three temperatures in the four seasons of the city.The highest temperature increase is summer,followed by spring and autumn,and the smallest in winter.As with the annual changes rules,the lowest temperature increase rate in the season is the highest,the highest temperature increase rate is the opposite.The intensity of urban heat island shows asymmetry changes.The features of Spatial distribution.The spatial distribution of the temperature change is generally the same.The typical village stations in the northern and southern are low-value areas of warming trends,and the urban-intensive areas in the Midwest regions are high-value areas with warming trends,which affect the obvious the warming effect of urbanization.(2)Impact of urbanization on precipitation changes(a)Changes in total precipitation.The annual precipitation of urban and rural stations all showed an in apparent weaker growth trend in the fluctuations.The UMR sequence of annual precipitation showed a slight increase,but urbanization had no significant effect on the annual precipitation.The UMR of precipitation in spring and summer is increasing,while in autumn and winter is decreasing,which shows that urbanization has the tendency of increasing the precipitation of the city in spring and summer.In terms of spatial distribution,the variation trend of precipitation in a year and four seasons is quite different,and the high values of variation trend in the summer and autumn is mainly located in the Midwest,but in winter which was opposite.(b)The changes of rainfall days.Compared with precipitation,urbanization has more significant effects on precipitation days.The UMR sequences of the precipitation days of the year and the four seasons are both decreasing.The urbanization reduces the number of precipitation days,but the total rainfall does not change significantly,but the rainfall intensity increases.In terms of spatial distribution,the high values of precipitation days in a year and the seasons of winter,spring,and autumn are mainly located at the Midwest of the country;summers are mainly located at the East.(c)Graded precipitation changes.With rainfall from mild rain to heavy rain,the UMR sequence of days(quantity)of precipitation gradually changed from a decreasing trend to an increasing trend.Urbanization increases the number(amount)of heavy rainfall events and decreases the number(amount)of mild precipitation,which leading to polarization of precipitation,extremes enhanced and urbanization make the spatial distribution of precipitation more obvious.In terms of spatial distribution,with the increase of rainfall intensity,the stations that with an increasing trend of precipitation(days)began to increase from the east.From mild rain to moderate rain,the high value area of precipitation changes from east to mid-west,and the the two High-value areas of precipitation days of are both located in the Midwest of the country;from heavy rains to rainstorm,the trends of precipitation(days),change from the east to the urban agglomeration of the Midwest.In general,precipitation was less affected by urbanization than temperature.(3)The influence of urbanization on the change of relative humidityUrbanization makes the relative humidity of urban stations decrease,so the effect of the urbanization is significant.The UMR sequences of relative humidity showed a downward trend in both the year and the four seasons,and the decline was more notable in summer and autumn.The city gradually presents"dry islandization".In terms of spatial distribution,the relati ve humidity in the urban agglomeration of the Midwest.showed a more declining trend of relative humidity,which was more"dry",which is the high value zone for relative humidity changes;the relative humidity of southern and northern rural stations showed a weaker downward trend.,which is the low value zone for relative humidity changes(4)Effect of Urbanization on Wind Speed ChangeUrbanization makes the average wind speed in urban stations decrease,and the role of urbanization is significant.The UMR sequence of annual wind speed is decreasing,and the urbanization has the effect of reducing the wind speed at urban stations.In terms of spatial distribution,the average wind speed reduction trend is more obvious in urban agglomeration in Midwest,which is the high value zone for the average wind speed changes,the average wind speed in the southern and northern rural stations shows a downward trend,which is the low value zone for the changing trend.(5)The Influence of Urbanization Reflected by Urbanization Development Composite Index on Meteorological ElementsThe integrated index of urbanization development has the best fitting efficiency with temperature,then the relative humidity and wind speed,but the the worst effect on precipitation.which shows that urbanization has the most obvious impact on temperature,followed by relative humidity and wind speed,and has least effect on precipitation.The influence of urbanization on the climate accords with the environmental Kuznets curve to some extent.This is basically consistent with the conclusion of the influence of urbanization on meterorological elements,which is analyzed by the UMR method. |
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