| Urban area in Fuzhou expanded 4.2 times from 1990 to 2015.Urban warming caused by the urban sprawling has been attentively concerned by the scientists and urban inhabitants.The Urban summer temperatures in Beijing,Shanghai,Guangzhou cities have been increased fastly with the urban development in recent 20 years.As the capital of the coastal city,The dynamic change of urban landscape elements,the urban heat caused by urban expansion,and the quantitative relationship between landscape elements and urban warming in Fuzhou,are the focus of the paper.The paper studied the change of the summer land surface temperature,the impervious surface coverage,the vegetation coverage and their relationships during 1994-2015 by use of Landsat images in Fuzhou.The results are listed as following.(1)Dynamics of urban landscape during 1994-2015:Impervious Surface Coverage(ISC)in the study area increased from 43.59%to 54.24%with the average annual growthrate of 1.16%.From 2008 to 2015,the average annual growth rate of ISC was 5.36%.Chengmen town and Jianxin town of Cangshan district are the hot built areas,the average growth rates of ISC in the two towns were 2.45%and 2.17%respectively.Furthermore,the Vegetation Coverage(VC)increased from 54.48%to 55.48%with an average annual growth rate 0.15%.Specifically,the annual growth rate of VC in Taijiang district was 4.24%whereas declining at rate of 1.65%and 2.02%in Cangshan district and Jianxin town respectively.(2)Changes of urban Land Surface Temperature(LST)during 1994-2015:The normalized temperature decreased from 0.34 to 0.28.Spatial variation of surface temperature change is obvious.The temperature of Mawei and Jinan District decreased significantly;for instance,normalized temperature of Mawei District decreased from 0.36 to 0.25.the normalized temperature in traditional downtown such as Gulou and Taijiang District decreased too.The average temperature rose up in the urban expanding zones incuding Gaishan town and Chengmen town in Cangshan district.(3)The dynamic characteristics of the areas classified with the landscape elements ISC and VC:Areas of the first class,the fourth class and the fifth class of ISC respectively increased 58.49km2,59.07km2,21.43km2;Areas of the second class and the third class of ISC respectively reduced 42.68km2 and 97.31km2.Areas of the highest VC and the low VC increased 80.16km2and 12.33km2,while areas for the secondly high VC and the Middle VC decreased 62.08km2 and 30.01km2 respectively.Therefore,when the urban area(the first class of ISC and low VC)was expanding,the ecological areas with high VC and the fourth or fifth class of ISC also spread at the meantime,while the traditional transferring area between urban and suburban or agricultural land in suburban was shrinking gradually.(4)The area change of the LST classes:the areas for the highest temperature zone and sub-moderate temperature zone increased by 73.50km2 and 104.69km2 respectively,areas for the sub-high temperature zone,the moderate temperature zone and the low temperature zone reduced by 28.25km2,128.89km2 and 21.05km2 respectively.(5)The spatial pattern change of the urban landscape elements and the surface temperature:patch shape and division indexes for ISC,VC,and LST decreased,while cohesion index for ISC,VC,and LST increased by 3.41,4.22 and 2.25 respectively.(6)The thermal effect of the urban landscape elements:Based on the pixel unit,in recent 20 years,ISC had a significantly positive correlation with LST,LST that rises by 0.40? with the 1%increasing of ISC,while VC was negatively correlated with LST,LST which decreases by 0.11? with the 1%increasing of VC.Through Multiple stepwise regression analysis,it was found that the average LST will rise by 0.33? if ISC and VC increase by 1%at the same time.(7)Thermal effects of urban landscape spatial configuration:For the fist class patches of ISC and the patches with the highest VC,their landscape indexes such as CA,COHESION,DIVISION significantly regulated the LST.For example,in 2015,if CA,COHESION and DIVISION indexes of the first class ISC rise 1 units,LST will change 0.78 ?,0.10 ? and-6.96 ?.If CA,COHESION and DIVISION indexes of the highest VC rise 1 units,LST will change-1.05 ?,-0.11 ? and 10.7?.Therefore,the warming effect of ISC and the cooling effect of VC would be varied with their spatial patterns,and Changing the CA and DIVISION of landscape patches(ISC or VC)in urban planning can effectively mitigate the urban warming. |
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