The Impact Of Urban Green Area On Thermal Environment

The continuous increase of urbanization has led to a rapid rise in the city,which has seriously affected the quality of the urban ecological environment and the lives of residents.Urban green areas can alleviate the thermal intensity in the surrounding area and improve human comfortless.As the core area of Beijing,the area within the 5th ring experiences rapid construction and development and a large population capacity.Therefore,it's of great significance to explore the dynamic changes of the urban green area and its influence on the thermal environment within the 5th ring road in Beijing.It will facilitate the establishment of eco-friendly approaches to alleviate urban thermal stress.In this paper,using remote sensing images from the five periods of summer(July)from 1999 to2017,taking the areas within the 5th ring road as the object,this paper explores the characteristics of the temporal and spatial evolution of surface temperature,clarifies the difference in surface temperature under different land-use types,and accurately analyze the correlation between the cold island effect of urban parks and its landscape pattern characteristics.The main findings of this article are as follows:(1)From 1999 to 2017,the time change of the thermal environment in the 5th ring road was generally divided into two stages.From 1999 to 2011,the area of the high-temperature zone and the extremely high-temperature zone gradually increased,and the thermal environment condition improved from 2011 to 2017.In terms of spatial changes,the areas with higher surface temperatures in 1999 were concentrated in the second ring road and gradually moved outward after 1999.By 2011,high temperature and extremely high-temperature areas were concentrated in the area south of the middle between the third and the 5th ring road.In 2017,the overall thermal environment within the 5th ring road has improved to a certain extent.(2)From 1999 to 2017,the proportion of grassland and water body area did not change significantly,the proportion of bare land area gradually decreased,the proportion of impervious surface area showed an overall rising first and then falling,and the proportion of woodland area gradually increased.In terms of spatial changes,from 1999 to 2005,the bare land area decreased.The northeast area between the 4th and 5th ring road changed from impervious and bare land to forest land,while the woodland in the southeast area changed to impervious surface.In 2009,bare land within the 5th ring road was only scattered in the area between the 4th and the 5th ring road.From 2009 to 2011,the spatial pattern has no significant change.In 2017,the area of woodland within the 5th ring road increased significantly and impervious surface area decreased.(3)The average surface temperature of each land-use type is water,woodland,grassland,bare land,and impervious surface from low to high.The ratio of woodland and impervious surface area is an important factor affecting the thermal environment within the 5th ring road.Using the CA-Markov model to predict the land-use pattern in 2035,we can see that in 2035,impervious surface and woodland will be the main land-use type within the 5th ring road(the total area accounts for >94%).According to the correlation model between land use and surface temperature,the surface temperature in 2035 is 44.13 ?.(4)The average temperature inside the selected 73 parks was 40.76 °C,which was 5.21 °C lower than the average surface temperature in the same year.The internal temperature of the park is mainly affected by the area and shape of the park.The average cooling distance of 73 parks is 0.40 km,the average cooling range is 4.52 ?,and the average cooling gradient is 12.88 ?/km.The larger the park area,the higher the proportion of internal and external woodland and water bodies,the lower the proportion of impervious surface,the more complex the shape,the more scattered the internal and external patches,the better the cooling effect of the park on the surrounding area.In addition,through the stepwise regression analysis of the urban park landscape pattern indicators and their cooling effect,a correlation model about the cooling distance,cooling range,and cooling gradient of urban parks is obtained.The fits are 0.75,0.79,and 0.68,respectively,which can better interpret the cooling regular pattern of urban parks.This paper explores the regional thermal environment changes and mitigation measures within the5 th ring road in Beijing,obtains the correlation model between land use and surface temperature,and the cooling effect model of urban parks,hoping to provide a reference for improving the urban living environment and planning urban land.