Research On The Impact Of The Evolution Of The Spatial Structure Of Lanzhou On The Thermal Environment

With the continuous development of society,the urbanization is growing in intensity,which leads to profound changes in the urban spatial structure.The urban spatial structure is closely related to the urban thermal environment and plays a leading role in thermal environment of the city.Illustrating by the case of Lanzhou,9 groups remote sensing satellite image data of landsad4-5 TM and Landsat 8 are classified by using SCNN classification method and the Arc GIS 10.1 and the ENVI 5.0 software.And the Spatiotemporal analysis of Spatial Structure of Lanzhou follows,which focus on the analysis of impervious surface changes.Then,using the radiation transfer equation method and the mono-window algorithm to invert the surface temperature of Lanzhou City,the obtained data were selected and normalized to obtain the Lanzhou City surface temperature thermal level,and the characteristics of space-time changes of thermal level of Lanzhou City during the past 26 years was analyzed according to the thermal level,focusing on the evolution of the normal temperature region and the law of migration of the center of the high temperature area.Finally,the influence of the spatial structure of Lanzhou City on the thermal environment was analyzed and expounded.The primary research conclusions are as follows:First,from 1990 to 2016,the quantity changes of urban spatial structure space in Lanzhou: the area and the proportion of impervious surface was increasing,the area and the proportion of bare land,water area,and vegetation were decreasing continuously;In terms of the speed changes: The average annual expansion rate,average annual growth rate,and single-land use type dynamic degree of impervious surface show positive growth,the data fluctuation is stable,the average annual growth rate and average annual growth rate of bare land,water area,vegetation,and the dynamic degree of single land use type show negative growth,which shows significant fluctuations.Among them,the vegetation was the most prominent and the data in the water area fluctuate smoothly.In terms of the number of spatial structures transferred,bare land was the main transfer target,the impervious surface is the main transfer object.From 1990 to 2016,the impervious surface quantity data of Lanzhou : The impervious surface area in 2016 was 2.064 times that of in 1990,with a total expansion of 71.663km2.;For the expansion strength and the space expansion direction: Generally speaking,the impervious surface of Lanzhou was developed rapidly.The main direction of expansion is: east and north,Northwest,and Southeast;For the center migration: During 26 years,the center of impervious surface structure in Lanzhou is in the Qilihe District or the Mars Street(central-northwest(1994)-southeastern(2008)-northwestern(2016)).Second,from 1990 to 2016,the quantity changes of thermal level in Lanzhou: the area and the proportion of low-temperature and normal-temperature areas increased,the proportion of normal-temperature areas accounted for the largest proportion,and the areas of sub-low temperature,sub-high temperature,and high-temperature areas decreased continuously,and their proportions of area decreased too,at the same time,the proportion of sub-low temperature area decreased most than others;For the rate changes: the annual average expansion speed and growth rate of low temperature and normal temperature area showed positive growth,and the data fluctuation in normal temperature area was relatively stable.The annual expansion speed and growth rate of the sub-low temperature zone,sub-high temperature zone,and high temperature zone show a negative growth,the data fluctuations in the sub-high temperature zone and the high temperature zone were obvious,the sub-high temperature zone was the most prominent,the data fluctuation in the sub-low temperature zone is stable,and the spatial structure shifts.Quantity changes of spatial structure transform: The sub-high temperature zone is the main target for the transform,and the normal temperature zone is the main transfer target.From 1990 to 2016,the number of normal temperature districts in Lanzhou: The area of normal temperature in 2016 was 1.532 times than in 1990,with a total expansion of 35.014 km2.;in the direction of expansion strength and spatial expansion,generally the normal temperature zone district of Lanzhou developed rapidly.The main expansion directions are: Southeast,west,and east;For the high temperature area migration center of Lanzhou: 1990 Anning District Northwest Normal University-2008 Qilihe District Lanzhou First People's Hospital-2016 peace District Jian ning West Road(1990-Center of the Southeast(2008)-Northwestern(2016)),and the trend of change is basically the same as that of the impervious surface center.Thirdly,basing on the influence of the urban spatial structure on the thermal environment,bare space has been distributed in all five thermal level spaces all years,but more than 78% is distributed in the normal temperature zone,and the sub-high temperature zone;The impervious surface are also distributed across five thermal level spaces all years,of which 90% are distributed in the normal temperature zone and the sub-high temperature zone;More than 80% of the water area is in the low temperature zone,and the water zone accounts for the low temperature zone area over time.The proportion increased gradually,and did not appear in the sub-high temperature zone and high temperature zone;more than 80% of the vegetation area was in the sub-low temperature zone and normal temperature zone,of which the sub-low temperature zone is dominated,but did not appear in the high temperature zone;According to the contribution degree of the thermal environment which is closely related to the urban spatial structure: the impervious surface contribution rate is the largest in the calendar year,it is rising constantly,and the contribution of bare land,water areas,and vegetation is continuously declining,among which the contribution of the water area is the minimum.In general,impervious to water has a greater impact on temperature.Bare land and vegetation have less impact and watershed has the least impact.From the contribution index of thermal effect,the impervious surface> bare land> vegetation> water area;the thermal unit weight index indicated: impervious surface> bare land > vegetation > water area.Therefore,the impervious surface in the spatial structure of Lanzhou is the one that has the greatest impact on the thermal environment of Lanzhou;the water area is the one that has the least impact on the thermal environment of Lanzhou.