以形态学视角,厘清城市绿色空间(urban green spaces,UGS)与地表城市热岛(surface urban heat island,SUHI)形态演化的关系为存量背景下如何微调绿地改善城市热环境提供了新途径.本文以西安市建成区为例,基于形态学空间格局分析法,分析2002-2021年UGS形态演化特征,同时识别SUHI范围,以地表城市热岛扩张指数拆分SUHI形态演化过程.在此基础上,采用皮尔逊分析法与随机森林模型相结合的方式,探讨UGS与SUHI形态演化的动态关系,同时参照西安市国土空间总体规划草案,提出具体的UGS改造方案并进行空间落位,进而预估改造措施实施后的效果.结果表明:①2002-2021年,UGS面积缩减,整体呈现大斑块破碎,小斑块消失,相互间连通性降低的趋势.②2002-2021年,地表温度最高值逐年攀升,温度增幅下降;SUHI覆盖范围蔓延程度大于收缩程度.SUHI收缩由建成区中央点状收缩转变为建成区边缘点状收缩.2002-2012年,边缘式扩张为主要扩张类型,存在于城市边缘地带,2012-2021年,边缘式扩张和填充式扩张比例相当,在研究区均匀分布.③除孤岛外,各类UGS与SUHI形态变化呈极显著负相关关系.其中,核心区、桥接区贡献度较大;核心区主要作用于SUHI边缘式、填充式扩张,桥接区同时作用于SUHI填充式扩张和收缩.④未来绿地优化应着眼于碎片化空间,在易于形成SUHI边缘扩张的城市边缘地带,保证核心区的连通性,在易于形成SUHI填充扩张的中心城区,注重桥接区、孤岛等细碎斑块的合理联系.⑤"点对点"式绿地更新改造后,各类UGS均有不同程度的增减,总体而言降温效果良好.
Study on the relationship between green space and surface heat island evolution in urban built-up areas based on morphology:The case of Xi'an city
From a morphological standpoint,elucidating the relationship between the morphological evolution of UGS and SUHI offers a novel avenue for fine-tuning green spaces to ameliorate the urban thermal environment amid stock reduction.This study takes the built-up area of Xi'an city in China as the research area.Initially,employing Morphological Spatial Pattern Analysis(MSPA),this paper examines the characteristics of UGS morphological evolution from 2002 to 2021.Subsequently,it identifies SUHI coverage,and disaggregates the SUHI morphological evolution process using the Urban Heat Island Expansion Index.Building upon this,we explore the dynamic relationship between UGS and SUHI morphology evolution by combining the Pearson Correlation Analysis method with the Random Forest model.Simultaneously,we reference the Draft Public Consultation of the Overall Land and Space Planning of Xi'an city,propose specific UGS transformation plans with spatial allocation and estimate the effects after taking the renovation measures.Findings indicate a decrease in the UGS area from 2002 to 2021,with an overall pattern of larger patches fragmenting and smaller ones disappearing,thereby diminishing interconnectivity.During this period,surface temperature peaks rise,with a decreasing temperature increment.SUHI coverage exhibits greater expansion than contraction.SUHI contraction shifts from central point-like to peripheral point-like within the built-up areas.From 2002 to 2012,the edge expansion was the primary type of expansion,which occurred in the peripheral zones of the city.From 2012 to 2021,the proportions of the edge expansion and the infilling expansion were similar,and they were evenly distributed across the study area.Except the islet,there was a highly significant negative correlation between the morphological changes of various types of UGS and SUHI.Among them,excluding the core,small patches(such as bridges)made a significant contribution.The core primarily influenced the edge expansion and infilling expansion of SUHI.The bridge simultaneously affected the infilling expansion and contraction of SUHI.In the future,green space optimization will focus on fragmented spaces.Urban peripheries prone to SUHI edge expansion should ensure connectivity in the core,and central urban zones susceptible to SUHI infilling expansion should emphasize rational connections among fragmented patches like bridges and islets.After the"point-to-point"green space renewal and renovation,all types of UGS have been increased or decreased to different degrees,and the cooling effect is generally good.
morphological spatial pattern analysisurban green spacesurface urban heat islandheat island expansion
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