高原城市生态建设对“热岛效应”的减缓作用——以西宁市为例

The mitigation effect of plateau urban ecological construction on“heat island effect”:a case study of Xining City in Qinghai Province of China

快速城市化加剧了城市的热岛效应,而城市生态建设可减缓城市“热岛效应”。本文以地处青藏高原东北部的高原最大城市西宁市为例,基于2000—2019年Landsat遥感影像数据,对城区夏季的地表温度和植被覆盖度的变化进行了对比分析,并依据城区林地、草地的植被覆盖度、水域面积的变化和反演的地表温度,修订了高原城市林地、草地和水域的降温效应模型,估算了西宁市城市生态建设对城市“热岛效应”的减缓效应,结果显示:2000—2019年,西宁城市植被覆盖度整体呈现上升趋势,水域面积不断扩大,城市热岛面积呈现先上升后下降的趋势,城区林地和草地的区域平均降温效应分别为2.12℃和4.29℃,水域的区域平均降温效应为2.19℃,高原城市的生态建设对减缓城市“热岛效应”效果显著。

Background,aim,and scope With global accelerating urbanization process and the development of social economy,the urban heat island effect is becoming increasingly acute.After rapid urbanization for past several decades in china,the urban scale and built-up area have grown rapidly,which has intensified the urban heat island effect.Therefore,constantly enhancing the level of ecologicalization and constructing an eco-city,which is fit to dwell for human being,have become the core content during the urban ecological construction.However,the Qinghai-Tibetan Plateau as the most important ecological barrier,its ecological environmental protection and ecological civilization construction are essential foundations for China’s sustainable development.Owing to special ecological environment and ecological status,the urban ecological construction of the Qinghai-Tibetan Plateau has become a key concern.In this study,Xining City was selected as study area,it located on the Northeastern of the Qinghai-Tibetan Plateau,and is the largest city in this plateau region.Materials and methods Adopting the Landsat remote sensing data during the period of 2000—2019 to analyse surface temperature and vegetation coverage fraction in summer of this study area.Employing the random forest method to interpret land use types.In addition,the corresponding temperature model were obtained by linear fitting,which used to calculating mitigation effect of the heat island effect to the urban ecological construction.Results The results showed that the area of urban heat island in Xining City showed a trend of first increasing and then decreasing during the study period.And the vegetation coverage fraction is on the rise and the water area is expanding.In addition,the regional average cooling effect of forest land,water area,and grassland in Xining City was 2.12℃,2.19℃and 4.29℃,respectively.Thus,the overall ecological construction of Xining City can alleviate the urban heat island effect.Discussion During the 19 years,the urban heat island area of Xining City showed a trend of first rising and then falling.The overall the vegetation coverage fraction showed an upward trend.The proportion of medium to high vegetation coverage fraction and high vegetation coverage fraction reached its peak in 2010 and 2005,respectively.Ecological construction should adapt to the speed of urban construction,although the process of environmental effect is relatively slow,ecological construction plays an important role in realizing sustainable development of urban environmental friendliness and livability.Conclusions The vegetation coverage fraction and water area of Xining City are continuously expanding.Under the urban development trend of rapid expansion of built-up area,urban heat island effect is obviously controlled and alleviated,which is closely related to urban ecological construction.The results of urban ecological construction between 2000 and 2019 are relatively obvious.Recommendations and perspectives The traditional concentrated greening is transformed into a uniform layout.In the old city reconstruction,a large number of trees should be planted,and should be made to afforestation the roofs and walls of buildings,widen the existing river channels and increase constructed wetlands.