Study On River Network Vulnerability And Its Thermal Environmental Effects In Shanghai

The natural function,landscape ecological function and social service function of river network have been playing an important role in Shanghai development.Since Shanghai’s Open Port,the river network has been singleness and mainstream under the human disturbance.And it has a negative impact on hydrology,climate,landscape ecology,shipping and other aspects.The river network morphological structure and ecological environment have aroused widespread concern in society and academia.The research on the evolution,evaluation and function of river network can be comprehensive,multi﹣level understanding the relationship between urban development and river network.It has important practical and theoretical significance.By consulting literature and historical data,using GIS technology to construct the Shanghai Old Town Area historical river network.Based on 1965,1994 and 2013 Land use data,this paper expounds the river network evolution and influencing factors in the historical period and recent decades.Taking vulnerability as the breakthrough point,the assessment framework of river network vulnerability PSR model is built.The river network vulnerability and spatial distribution are analyzed by using Arcgis spatial analysis tool.And the impact of land use patterns is discussed.In order to analyze the river network thermal environmental effects,the study area is located in inside the Shanghai outer ring road,and Landsat remote sensing image is the data base.The temporal and spatial variation characteristics of the thermal environment between season and main stream are discussed.The relationship between land cover type,river network and surface temperature is also analyzed.Its"Cold Island Effect"and influencing factors are studied.The main conclusions of this paper are as follows:(1)The Shanghai Old Town river network evolution can be divided into before Open Port and after Open Port.According to the change of the ratio between the all rivers length and the moat length,and its annual ratios,the river network evolution from the Open Port to before 1949 period can be divided into Preparation period(1875﹣1901),Beginning period(1901﹣1911),Rapid period(1911﹣1918)and Ending period(1918﹣1949).Because of the traditional economy town dweller’s ideological concept limitations,the river system evolution in Shanghai Old Town lags behind Concession.By analyzing the drainage density,surface water ratio,box dimension and other indicators in the central city(Zhabei and Hongkou district),near suburbs(Xinzhuang industrial district)and far suburbs(Huinan Town district)in 1965,1994 and 2013,it is found that the river network degradation in Zhabei and Hongkou district occurs from 1965 to 1994,with only minor changes from 1994 to 2013.The surface water ratio in Xinzhuang industrial district is comparatively consistent the two period,but the river length and box dimension are not comparatively.From 1994 to 2013,the river network evolution rate in Huinan Town district is significantly faster than that in 1965 to 1994.(2)Urbanization has caused obvious differences in characteristics between Shanghai’s regions.The drainage networks in Pudong and Qingpu areas are densely,but in the central city is sparseness.The river network vulnerability radiates from the central city high to suburbs low.The vulnerability degree area proportion of is ranked as follows:slight vulnerability(31.93%)>moderate vulnerability(22.71%)>micro﹣vulnerability(20.71%)>severe vulnerability(20.26%)>extreme vulnerability(20.71%).The river network vulnerability exists spatial aggregation and has obvious spatial heterogeneity.There is a clear boundary between the high and low river network vulnerability.The four land cover types are significantly correlated with river network vulnerability.Construction land is the main driving factor for the change of the river network vulnerability.(3)On the seasonal time scale,the spatial distribution of land surface temperature is quite different.It has high same degree between spring and summer.Spring and summer land surface temperatures differs spatially from that in autumn and is completely different from that in winter.The Huangpu River and other rivers have obvious low temperature corridors in spring and summer,but not in autumn and winter.The water surface temperature is the lowest in spring and summer,and the lowest in autumn and winter is urban green space.According to the study on DI and the relationship between land use area proportion and surface temperature,land use types has less impact on surface temperature in autumn and winter,but has more impact in spring and summer.The water area with the best cooling effect in spring,summer,autumn and winter accounts for0.20,0.35,0.20 and 0.15.The construction land area with the best cooling effect in spring,summer accounts for 0.70.The correlation degree between surface water ratio and land surface temperature is obviously higher than that of drainage density.When the surface water ratio increases by10%,the surface temperature decreases by 0.9682℃and 0.6880℃in spring and summer respectively.In spring and summer,the river area,river width and river velocity have a good correlation with river surface temperature and the cooling effect.According to the cooling effect study on 22 municipal rivers,water average temperature drop gradient in the spring,summer,autumn and winter is 7.24℃/km,7.55℃/km,2.95℃/km,4.25℃/km.When river width increases 10 m,spring and temperature drop amplitude increases 0.56℃,0.56℃,respectively.When river area increases 1km~2,spring and temperature drop amplitude increases 2.56℃,1.94℃,respectively.When river velocity increases 0.1m/s,spring and temperature drop amplitude increases 1.63℃,1.48℃,respectively.The study of cooling effect of Huangpu River shows that there are some differences in cooling effect between east coast and west coast.