Temporal And Spatial Patterns Of Thermal Environment In The Yangtze River Delta Urban Agglomeration And Its Impact On Ecological Security

The process of urbanization has an important influence on the regional thermal environment,so evaluating the ecological security pattern of urban thermal environment scientifically is of great significance to the regional thermal environment and urban planning.In this paper,MODIS land surface temperature and land use data were used.Firstly,the thermal landscape spatial-temporal pattern of the Yangtze River Delta urban agglomeration were analyzed.Secondly,the spatialtemporal variation characteristics of the Yangtze River Delta urban agglomeration were analyzed by using UHII and UHI footprint.Finally,we constructed the ecological security assessment model based on thermal environment in order to evaluate the temporal and spatial patterns of thermal environment and ecological safety in the urban agglomeration of the Yangtze River,combined with the method of landscape ecological security assessment and the characteristics of thermal landscape's quantity,morphology and structure,we used the CA-Markov model to predict the thermal environment,and the ecological environment security pattern of the urban agglomeration in the Yangtze River Delta in 2020 is also predicted.The main conclusions are as follows:(1)The high temperature zone and sub-high temperature zone of the Yangtze River Delta urban agglomeration were concentrated in the built-up area and the surrounding suburbs.Meanwile,the sub-high temperature zone and high temperature zone distributed widely in summer,followed by spring and autumn,and the least widely in winter.During 2005 to 2015,the low temperature zone,the sub-high temperature zone and the high temperature area showed an upward trend,while the low temperature area showed a downward trend.At the same time,summer and winter were the two seasons of the most obvious changes in the high temperature zone and high temperature zone,the high temperature zone and high temperature in summer was increased first and then decreased;the high temperature zone in winter showed an upward trend,the high temperature zone increased first and then decreased,and the high temperature zone showed a southward trend.(2)A low temperature zone,medium temperature zone and high temperature zone with low temperature zone and high temperature zone had a more complex shape and boundary contour,at the same time,around the low temperature zone,medium temperature zone and high temperature zone with low temperature zone and high temperature zone for better of aggregationand more patches.During 2005 to 2015,the index of low temperature zone and high temperature zone shape and perimeter area fractal dimension increased first and then decreased from 2005 to 2015,the summer low temperature zone and high temperature zone shape and boundary of the changed most obvious;In low temperature zone and high temperature zone interspersion and juxtaposition index showed an upward trend,the low temperature zone and high temperature zone aggregation index showed an upward trend from 2005 to 2015;the summer low temperature zone and high temperature zone walking was significantly decreased,the thermal polymerization of summer patch grades worse,while in winter,the thermal polymerization of can be better for grade plaques.(3)The intensity of UHI in Yangtze River Delta city group showed the decreased first and then increased trend from 2005 to 2015;the summer heat island intensity is the strongest,followed by spring,autumn,with the lowest in winter.During2005 to 2010,the spring and winter heat island intensity increased significantly,during 2010 to 2015 the summer and autumn heat island intensity increased significantly.During the period of 2005-2015,the urban heat island footprints of the Yangtze River Delta urban agglomeration showed an increasing trend.For the season,the summer heat island was the highest,followed by the spring and autumn,and the lowest in winter.(4)The distribution characteristics of urban heat environment of ecological security spatial pattern in Yangtze River Delta city: high risk areas were mainly concentrated in the built-up area and suburban distribution;medium risk areas are mainly distributed widely in the north of the Yangtze River plain area,the south part of cloth city group was scattered;low risk areas are mainly concentrated in the Gaoyou lake,Taihu and Qiandao Lake waters,south city group part of the hilly area were widely distributed.The area of high risk and low risk areas showed an upward trend in 2005-2015,and the medium risk areas were decreased."Z" region has the slip situation significantly of thermal environment ecological security.It is high risk area occupied the medium risk region,especially the coastal area high risk areas tend to contiguous distributions.Shanghai and Wuxi city is the two cities with the worst ecological security of regional thermal environment,high risk areas accounted of the total area of 82.66% and 91.98%,respectively.It almost covers the whole city.The growth rate of the north urban agglomeration in the low risk area was obvious in the first 5 years,but in the last 5 years,Hangzhou and Hangzhou increased obviously in the last 5 years.(5)In 2020,high risk areas in "Z" region are further expanding,and the medium risk areas reduced obviously;Hangzhou and Hangzhou in the mountainous region showed an downward trend;the Yangtze River to the north plain area change not obvious.