21世纪以来西安城乡梯度土地覆盖变化及对城市热岛影响时空特征

Spatiotemporal Pattern of Urban-rural Aradient Land Cover Changes and Their Impact on Urban Heat Island in Xi’an City Since the 21st Century

城市快速扩张导致城乡梯度土地覆盖发生显著的变化,引发不透水地表的增加,植被覆盖的减少,从而加剧了城市热岛强度。研究城乡梯度土地覆盖变化引起的城市热岛效应,并揭示城市热岛的时空特征及强度的变化,对城市规划建设、人居环境改善及提升城市生态系统服务功能具有重要的意义。基于Landsat系列4期影像,利用单窗算法反演西安市地表温度,计算热场变异指数得到热力场强度图并对其进行等级划分,结合土地利用/覆盖类型数据分析城乡梯度土地覆盖变化对城市热岛强度的影响。结果表明:①2000年西安市极强热岛效应区占研究区面积的10.58%,逐渐增加到2011年极强热岛效应区域的面积占比达到16.14%,而后到2015年降低为9.00%,整体上西安市城市热岛效应呈现出了先增长后降低的趋势;②2000年到2015年城乡建设用地面积增加了412.76 km2,极强热岛强度的范围随城市建成区的扩张逐年向外扩展;③无热岛效应区约70%位于耕地和林地,水域在无热岛效应中的占比也在逐年增多,从31%增加到了47%。不透水地表面积占比与地表温度有显著相关性,城乡梯度植被和水体面积的增加可以有效地缓解城市热岛强度。

Rapid urban expansion had a significant impact in land use/cover change along urban-rural gradient,and the increase of impervious construction land and the reduction of vegetation cover had induced and aggravated the urban heat island effect. Studying the impact of urban-rural gradient land cover change on urban heat island effect was significant for urban planning and construction,improving the comfort of human settlements and enhancing the function of urban ecological services. The surface temperature of Xi’an city was retrieved by mono-window algorithm based on Landsat images,and the thermal field intensity map was obtained by calculating the thermal field variation index,and the gradient land cover changes in urban and rural areas were analyzed with land use data. The results showed that:①The urban heat island effect in Xi’an showed a trend of first increasing and then decreasing from 2000 to 2015. In 2000,the extremely strong heat island effect area accounted for 10.58% of the research area,and gradually increased to 16.14% in 2011,and then decreased to 9.00% in 2015. ② From 2000 to 2015,the area of construction land increased 412.76 km2 and the intensity of extremely strong heat island expanded year by year with the expansion of urban built-up areas. ③About 70% of the nonheat island effect areas were located on farmland and forest land,and the proportion of water area in the nonheat island effect was increasing year by year from 31% to 47%,which showed that the increase of vegetation and water area could effectively alleviate the urban heat island effect.