Tempo-spatial Pattern And Ecological Benefits Of Parks In Shanghai Based On Multi-source Data

Urban parks provided residents with abundant recreational places and alleviated mental pressure.Meanwhile,urban parks played an important role in maintaining urban ecological balance,mitigating urban heat island?UHI?effect and improving biodiversity.The research took the typical highly urbanized region,Shanghai,as the study area,whose basic park information was collected through network.Based on Baidu Map application program interface?API?,the locations and boundaries of parks in Shanghai were obtained,and then the parks were digitized and position rectified in ArcMap.On the basis,spatial pattern and spatial evolution characteristics of parks in Shanghai were analyzed.Afterwards,based on Landsat 8 remote sensing?RS?data,the thermal influence of parks in Shanghai such as maximum cooling range and maximum temperature drop were calculated through buffer analysis,and then the potential influencing factors were explored via k-mean cluster analysis and Pearson correlation coefficient.Moreover,based on multi-temporal and multi-source RS data,three newly-built country parks were chosen to evaluate the ecological benefit comprehensively,including the mitigation of UHI effects and ecosystem service value improvement,on contrast to the unbuilt situation.The main conclusions of this study are as follows:?1?260 parks in Shanghai were digitized up to June,2018.As to the distribution of parks,the quantity of parks showed the characteristic of Pudong New District?count:32?>suburb districts?count:14-32?>central districts?count:9-21?>outer suburb districts?count:5-9?,and 53.85 percent of parks were within the outer ring road of Shanghai.The quantity of newly built parks was changing in the pattern with two peaks and one valley,where the peaks of park construction were in the early liberation period and the beginning of this century.At the early stage,parks were mostly distributed along Suzhou River and Huangpu River,whose spatial pattern were of strong directionality.As the city scale and urbanization developed,the spatial pattern of parks in Shanghai changed from discrete to aggregated,with weakened directionality.Furthermore,high Kernel density area of parks in Shanghai extended from central urban area to the central urban area of suburban districts such as Jiading District,Baoshan District and Songjiang District.And the area with highest Kernel density of parks was the juncture of Jing'an District and Huangpu District,with a density of 0.97 parks per square kilometer.?2?Base on the Landsat 8 remote sensing data of 24^th August 2017,the average land surface temperature?LST?of parks in Shanghai was 39.24 degree Celsius.Generally,average LST of parks was highest in central urban area,middle in suburban town and lowest in suburban area.Based on the k-mean clustering of average LST of parks and 10 meters buffer zones in 1500 meters distance areas surrounding the park,Shanghai parks could be clustered into five categories,combined with the location characteristics of each categories,which could be summarized as:?i?the suburban town type,with LST rising first and then dropping sharply as buffer distance increased;?ii?the high urbanization type,with LST rising first and then remaining steady as buffer distance increased,and the LST was the highest overall;?iii?the transition type of suburbs,with LST rising first and then stabilizing as buffer distance increased,and overall the LST was sub-high;?iv?the suburban type,with LST decreasing fluctuatingly as buffer distance increased,and the LST was the lowest;?v?the riverside type,with LST decreasing fluctuatingly as buffer distance increased,and the LST was sub-low.?3?The average LST of parks in Shanghai was logarithmic to park area and park perimeter,and the linear fitting R² were 0.56 and 0.51 respectively.Meanwhile,the LST of parks and the LST of buffer zones were positively correlated with their respective internal forest area,Normalized Difference Vegetation Index?NDVI?and water area,while negatively correlated with their respective internal construction land area and Normalized Difference Impervious Surface Index?NDISI?.The average cooling range of parks was 157.08 meters,and the average temperature drop was 2.10 degree Celsius.However,the cooling area of parks only accounted for 2.38 percent of the total area of Shanghai,and was mainly concentrated in central urban areas.The cooling benefits of parks were related to the location as well as internal and external environmental differences of parks.When the NDVI of parks and buffer zones were similar and both in a high value,parks were the supplement of regional green space and played the role of maintaining LST at a low level together with their buffer zones.When the NDISI of parks was low and the NDISI difference between park and its buffer zone was huge,the cooling island effect of parks was prominent,and the maximum cooling range of the park would be increased.?4?Jiabei,Pujiang and Langxia country park all showed remarkable decrease of constructive land and increase of vegetation coverage after land consolidation and park construction.Jiabei country park showed remarkable improvement in ecological benefits overall,while Pujiang country park and Langxia country park both showed somewhat improvement in ecological benefits.The construction of country parks played an active role in the reduction of regional construction land,the increase of vegetation coverage,soil formation and protection,as well as the mitigation of thermal environment.At the same time,the functional orientation and the completion degree of country park construction had an impact on the improvement of ecological benefits.The higher the completion degree of park construction,the more obvious the mitigation of thermal environment.Water area also helped on the improvement of ecological benefits of country parks.Appropriate increase of water area in country parks could enhance the ecological benefits of parks to a greater extent.This study was helpful to understand the spatial layout of parks in Shanghai and its impact on thermal environment,as well as the ecological benefits and weaknesses brought about by construction of new parks.It provides a reference for the improvement of regional thermal environment as well as the layout of parks,and is helpful for the the planning and location selection of new parks in Shanghai.