Temperature Effect Of Urban Green Space Spatiotemporal Evolution In The City Of Fuzhou

Nowadays,rapid urbanization results in the urban heat island(UHI)where the extreme high temperature event(EHTE)occurs frequently and triggers a series of ecological environment problems.As a strong"force"to alleviate the UHI effect,the urban green space(UGS)plays a key role in maintaining the urban ecological environment and attracts more and more attention because of its cooling effect.Recently,the city of Fuzhou on the West Coast of the Straits has showed a continuous UGS degeneration trend and more and more severe UHI phenomenon.Fuzhou is now among the high temperature cities in China.To improve its thermal environment and ease the UHI effect,it is urgent to carry out research on temperature effect of UGS spatiotemporal evolution.In this dissertation,the UGS evolution,its temperature effect and the relationship with the land surface temperature(LST)in the main area of Fuzhou since 1993s were systematically analyzed combined with the integrated methods of remote sensing(RS),geographic information system(GIS),spatial analysis,landscape pattern analysis and mathematical statistical analysis.And the UGS consevation controlling system was also put forward as an effective strategy.The main research contents and conclusions are as follows:1.The distribution pattern of land surface temperature and its relationship with UGS were analyzed in the main area of Fuzhou by using the thermal infrared remote sensing analysis technology.(1)The spatial distribution of LST changed greatly with a clear expansion from urban cold island(UCI)to UHI supporting the concern that the UHI phenomena gets more and more severe.And its distribution and extension was basically consistent with the outline of the city.The UCI area decreased from 198.52 km~2in 1993 to 132.41 km~2 in2016,with the area reduced by 66.11 km~2 and the amplitude decreased by 33.30%.The UHI area increased significantly by 160.60%,from 23.53 km~2 in 1993 to 61.32 km~2 in2016.This was mostly attributed to the transfer from the low temperature region and the sub-low temperature region,with the volume of 5.16 km~2 and 29.00 km~2,respectively.(2)It was apparent that the LST profile lines in the main urban area of Fuzhou City presented the peak value and valley value intersects,and the characteristics of the"cliff"and"steep wall"were obvious.The non-UGS was mainly distributed in the peak position of the profile lines.The UCI was closely associated with the distribution of UGS which was much more consistent with the distribution of water and wetland.2.The spatiotemporal evolution of UGS and its effects were investigated based on remote sensing(RS)and geographical information system(GIS)techniques.(1)Because of frequent human activities and the rapid development of urbanization,the UGS fragmentation degree increased and prompted relative uneven development of the land use and land cover(LULC).The UGS area has shown a sharp decline,from157.60 km~2 in 1993 to 88.56 km~2 in 2016,with a reduction in area by 69.04 km~2 and a decrease in amplitude by 43.81%.The cropland areas accounted for the largest proportion of the total UGS area,followed by that of forest/grass and water,and the wetland area accounted for the least.According to the reduction proportion these landuse types were sorted as follows:wetland(62.96%)>forest/grass(59.60%)>cropland(38.67%)>water(33.84%).(2)The UGS evolution process was obvious in the study area from 1993 to 2016,with UGS Loss(80.50 km~2)>UGS Unchange(56.00 km~2)>UGS Exchange(21.10km~2)>UGS Gain(11.46 km~2).The area difference between UGS Loss and UGS Gain was 41.77 km~2 with the urban green space evolution process index(GEPX)as high as7.02 which suggested that UGS Loss area was far greater than that of UGS Gain due to the different levels and ways of the human activities to UGS.(3)In each period,the UGS evolution model mainly gave priority to the edge type,followed by the enclave type and the filling type.The region between 3 and 6 kilometers from the city center decreased the most significantly from 1993 to 2016.Therefore,the region between 3 and 6 kilometers should be noticed to prevent the UGS conservation area deterioration in the future.(4)Population growth and economic development stimulated the demand for more land resources objectively,and caused the rapid expansion of construction land,which accelerated and spurred the reduction of UGS.In addition,the government planning and the decision-making played a role in space layout and urban construction in the main area of Fuzhou City.3.The temperature effect differences of UGS evolution in the main area of Fuzhou was discussed combined with the qualitative and quantitative methods.(1)The cooling effect caused by different landuse types was varied with UGS>non-UGS.Different types of UGS affected water>wetland>forest/grass>cropland.There existed a threshold value of cooling efficiency(TVo E).According to the law of diminishing marginal utility,the cooling efficiency curve was fitted between the cooling intensity and the area of UGS patch.In 1993,2000,2008 and 2016,the resulting minimum area was 0.050 km~2,0.055 km~2,0.050 km~2 and 0.055 km~2,respectively,and the mean cooling intensity was 1.84?,1.83?,1.89?and 1.82?,respectively.(2)The cooling effect caused by different types of UGS evolution process varied greatly in the order of UGS Gain>UGS Unchange>UGS Exchange>UGS Loss.The calculation showed that the average cooling effect of UGS Gain was about-5.0?,while the warming effect of UGS Loss was about 7.0?,they resulted in different average temperature variations.The threshold value of urban green space loss area(TVo A)was0.04 km~2 by constructing the regression analysis model between UGS evolution process temperature effect index(GETX)and UGS evolution area,which means keeping the area of UGS Gain equal to that of UGS Loss can alleviate the UHI effect as long as the area of UGS Loss does not exceed the TVo A.(3)The warming contribution to LST by different UGS evolution model varied greatly in the order of edge type>enclave type>filling type.In each period,the high LST difference value caused by the edge type model and enclave type model was mainly localized in Cangshan District and Jinan District.It was between 4 and 7 kilometers from the city center.(4)The mechanism between UGS evolution and the temperature effect was investigated by construction of the temperature vegetation index(TVX)coordinate space in the study area.The UGS decreased with the reduction of vegetation coverage,and thus caused a positive effect on urban warming.For different types of UGS,the temperature variation caused by water was 0.94 times,1.15 times and 1.25 times that of wetland,forest/grass and cropland,respectively,although the change of the vegetation coverage of water was 60%,13.33%and 14.29%of the other three types of UGS.For different UGS evolution process,UGS Unchange,UGS Exchange and UGS Loss developed from the high vegetation index and low surface temperature to the low vegetation index and high surface temperature but the transition was reversed for UGS Gain.4.The influence of UGS landscape pattern on LST variation was explored based on the theory of landscape ecology.(1)From the perspective of the class-level index,the water,forest/grass and cropland with larger area,lower degree of landscape fragmentation and the more complex landscape shape would show lower average LST and could work better for alleviating the UHI effect.(2)From the perspective of landscape-level index,LST was significantly negative correlated with PD,LPI,LSI and SHDI but positively correlated with CONTAG and AI.Therefore,in order to reduce LST,a variety of different types of landscape should be set up as much as possible with a relatively low degree of polymerization.5.The UGS consevation controlling strategy system was proposed and the UGS consevation condition was quantitative evaluated at different times by performing comprehensive evaluation index of UGS consevation.(1)The evaluation index was up and down with big regional differences based on the synchronization characteristics from 1993 to 2016.There was certain unbalanced spatial distribution between the urbanization development level and UGS consevation.The urbanization in both Gulou District and Taijiang District was ahead of the UGS consevation.Whereas,the Cangshan District and Jinan District showed the opposite.And the synchronization index manifested in the order of Jinan District>Cangshan District>Taijiang District>Gulou District.(2)The corresponding LST was generally low when the UGS synchronization index was high and vice versa.The size of the index could reflect a regional LST level in some ways.And the results could provide theoretical support and reference for the UGS conservation controlling in different urbanization area of China.Fuzhou City was chosen as the research object by using a series of remote sensing images.The dynamic relationship between LST and UGS evolution process,type,evolution model and the landscape pattern was elaborated systematically based on remote sensing technology with the temperature vegetation index(TVX)as well as the multiple methods of geostatistics and landscape analysis as the auxiliary tool.Basically,the evaluation methodology of the UGS consevation condition and the controlling rules were put forward.The results can not only contribute to understand the UGS ecological value of effectively alleviating the UHI effect,but also provide beneficial references for the sustainable management of UGS planning practice which has both important theoretical significance and practical value.