The Relationship Of Green Space Patternand Landscape Structure With The Heat Island In Xi’an

In order to explore the relationship between urban green space and urban heat island and propose green space optimization strategies to deal with urban heat island,the urban green space in Xi’an city is taken as the research object,and the combination of macroscopic remote sensing and microscopic measurement is adopted,through extraction of normalized vegetation index and inversion of surface temperature by the remote sensing image of 2009,2013 and 2017 in summer and correlation and regression analysis to explore the relationship between green space pattern and heat island,and measure the cooling and humidification effects of different community configurations in park green space to analyze the relationship between landscape structure and heat island.The main conclusions are as follows:(1)From 2009 to 2017,Greenland in Xi’an occupied nearly one-third of the urban area,which is the most varied type of landform among the four types of features.It decreased by 2348.10 hm~2 from 2009 to 2013,and increased 3907.17 hm~2 from 2013 to2017;From 2009 to 2017,NDVI of urban green space of Xi’an in summer increased with the urban loop extrapolation,that is,first ring<second ring<third ring<around the city;The NDVI values of four quadrants in 2009,2013 and 2017 in turns is southeast>northeast>northwest>southwest,southeast>southwest>northwest>northwest,southwest>southeast>northwest>northeast;The standard deviation of NDVI in each ring road and quadrant increased year by year,which means the fluctuation of urban green space coverage increased year by year.(2)In 2009,the urban heat island(including the strong heat island and the heat island)of Xi’an in summer decreased with the extrapolation of the loop,that is,first ring>second ring>third ring>around the city.In 2013,except that the distribution of one ring heat island was high,the urban heat island increased with the extrapolation of the loop and the phenomenon of“hollow heat island”appeared.In 2017,the urban heat island was first ring>second ring>around the city>third ring;The strong cold island and the cold island were mainly distributed in the third ring and the city;the proportion of the heat islands in each quadrant from 2009 to 2017 was increased.The ratios of urban heat islands in the respective quadrants in 2009,2013 and 2017 are northwest>northeast>southwest>southeast,northwest>northeast>southeast>southwest,northwest>southwest>southeast>northeast.(3)Compared with the control point,during the daytime(7:00—19:00),the five plant communities had obvious cooling and humidifying effects and their effects were both as follows:Community C4>C1>C5>C2>C3.In terms of the lasting time of the plant communities’internal temperature lower than the control points’,community C4 was the longest,and C1,C2 and C5 followed,and C3 had the shortest duration;And as for the lasting time of the plant communities’internal relative humidity higher than the control points’,the longest duration to the shortest one was C4>C1>C5>C2>C3.At night,no obvious differences in temperature and relative humidity between the plant communities and the control point had found.(4)The urban green space pattern can alleviate the urban heat island effect,and the correlation coefficients obtained for three years are-0.776,-0.612 and-0.605,respectively,and they exist y=-14.842x+4.6676,y=-12.284x+3.4500 and y=-8.054x+2.7915 linear relationship.In the urban green space landscape structure,the complex layer structure is more conducive to alleviating the urban heat island than the single-structured community vegetation landscape,namely“Joe-Irrigation-Grass”>“Joe-Grass”;In the community vegetation landscape with the same level,the more broad-leaved trees contained in the arbor layer and the fewer coniferous trees are more conducive to alleviating urban heat islands,namely broadleaf>needle-wide mixed>needles.(5)In the optimization of green space pattern,it is recommended to adapt to the appropriate land,increase roof greening and vertical greening,focus on the surrounding area,northeast quadrant,and northwest quadrant,and pay attention to the ecological role of urban park green space;In terms of landscape structure,it is recommended that the internal plant landscape structure level of urban green space is developed to multi-layer.In the urban green space internal plant landscape structure,the arbor layer increases the choice of broad-leaved tree species,and the two-dimensional plane transforms into three-dimensional.