太湖流域城乡建设用地扩张的高程特征变化

文章以城乡建设用地扩张的高程变化为焦点,运用太湖流域1985、1995、2000 和2010 年4 期土地利用数据及90 m DEM数据,通过构建建设用地密度指数、增量比、扩张速度、扩张强度及建设用地高程指数等指标,探寻太湖流域城乡建设用地高程变化的空间分异特征及其演变规律,结果表明:建设用地流域整体扩张的热点从中等高程区向较高和较低高程区转移,且向较低高程区转移态势尤为凸显,流域空间分布上表现为流域东部下游平原河网及北部沿江的城镇密集区和南部苕溪上游山谷地带建设用地向较低高程区逐渐扩张的趋势,而在除苕溪外的流域其他上游山地丘陵区逐渐向较高高程区扩张;新区开发及新城建设推动着城乡建设用地快速扩张,适宜建设土地供给有限与土地财政驱动下用地需求旺盛之间的矛盾迫使建设用地扩张走向较低和较高高程区,尤其苏南城镇密集区向较低高程区转移趋势更显著;建设用地向低海拔地区扩张必然挤占自然蓄滞水空间,分割和阻塞自然行洪通道,且地势低洼处洪水易蓄难排,而高海拔地区扩张会加快汇流缩短下游洪峰时间,导致区域水文安全隐患和内涝事件频发.

The Elevation Characteristics Variation of Urban and Rural Construction Land Expansion in Taihu Lake Basin

This paper focuses on the elevation variation of urban and rural construction land expansion. It uses 1985, 1995, 2000 and 2010's land use data and 90 m resolution DEM data, and establishes evaluation indexes including density index, incremental proportion, sprawl rate, sprawl intensity index and evaluation index of construction land, to explore the characteristics of spatial heterogeneity and the evolution pattern of urban and rural construction land elevation changes in Taihu Lake Basin. The research results indicate that: the hotspot of construction land expansion has transferred from medium-elevated region to higher-elevated and lower-elevated region in the whole basin, of which the former trend is more significant. Spatially, construction lands distributing along the plain river network in the eastern downstream watershed, in the city and town concentrated areas along the Yangtze River in the north, and in the valley areas of upper reaches of Tiaoxi stream have the trend to expand to lower-elevated region. However, except for Tiaoxi stream basin, the other hill regions in the upstream basin are expanding gradually to higher-elevated zones. The development of new districts and cities has promoted a rapid expansion of urban and rural construction land. Contradiction between the limited supplies of suitable land for construction and the huge demand of land driven by land finance has forced the construction land to expand to higher and lower elevation areas, especially to lower areas in city and town concentrated areas in southern Jiangsu Province. Construction land expanding to lower altitude regions will inevitably occupy the natural water storage space, divide and obstruct the natural flood discharge channel, and lead to difficulties for flood to be discharged in the low-lying place. While construction land expanding to higher altitude regions will accelerate the confluence water and shorten the downstream flood peak time, which lead to regional hydrological security risks and frequent waterlogging disasters.