青藏高原城市扩展过程的区位因素——基于随机森林的多尺度分析

Location factors of urban expansion on the Qinghai Tibet Plateau-Multi-scale analysis based on random forest

过去几十年,青藏高原快速的城市扩展过程给生态环境带来了严重威胁。区位因素会影响城市扩展的空间格局,进而改变其对区域生态环境的影响。因此,认识青藏高原城市扩展过程的区位因素特征对于保护区域生态环境具有重要意义。在全区、生物群区和生态区3个尺度上分析了区位因素对青藏高原城市扩展过程的影响。基于长时间序列城市土地数据分析青藏高原城市扩展过程。利用随机森林模型分析青藏高原城市扩展区位因素特征。研究表明,青藏高原在1990-2020年期间经历了快速的城市扩展过程。全区城市土地面积从277.4 km^(2)增加到974.9 km^(2),增长了2.5倍。对青藏高原城市扩展影响最大的区位因素高程对城市扩展的重要性不断下降。与之相对,铁路因素的重要性迅速上升,其重要性从2.15%增长到10.56%,增加了3.9倍。然而,铁路建设在促进青藏高原城市发展的同时,也会对区域内近三成的濒危物种产生影响。因此,在青藏高原未来城市发展过程中,既要重视铁路对城市扩展带动作用,也要注意减少铁路对区域生物多样性的影响,进而促进高原的可持续发展。

In recent decades,the Qinghai Tibet Plateau(QTP)has experienced a rapid urban expansion,which has brought serious threats to the local ecology and environment.Location factors(e.g.topography,transportation and river,etc.)will affect the spatial pattern of urban expansion,and then change its impact on regional ecology and environment.Therefore,it is of great significance to understand the characteristics of the location factors of urban expansion for the protection of the ecology and environment on the QTP.In this study,we analyzed the impact of location factors on the urban expansion of the QTP at multiscale,that is,the whole region,the biome and the ecoregion.First,based on the long-term urban land dataset,we analyzed the urban expansion of the QTP.Second,the random forest model was used to analyze the location factors of urban expansion on the QTP.We found that the QTP experienced rapid urban expansion during 1990-2020.The urban land area of the whole plateau increased from 277.4 km^(2)to 974.9 km^(2),an increase of 2.5 times.Elevation was the most important location factor affecting the urban expansion of the QTP,and its importance was 30.1%.However,the importance of elevation to urban expansion declined from 1990 to 2020.In contrast,the railway factor was the location factor with the largest change in importance to urban expansion,increasing its importance by a factor of 3.9 from 2.15%to 10.56%.The study also found that the construction of the railway not only promoted the urban development of the QTP,but also affected nearly a third of the endangered species in the region.Therefore,in the future urban development process of the QTP,attention should be paid not only to the role of railways in driving urban expansion,but also to reducing the impact of railways on surrounding biodiversity,so as to promote regional sustainable development.