Spatial and temporal analysis of ecological security of Xi'an City

Based on ecological footprint method, an ecological tension index was put forward and ecological security assessment index established on the ecological security of Xi'an City from 1991 to 2003. The results show that the ecological state of Xi'an City in 1991 can be stratified into three: Ecological safety region, including Zhouzhi and Lantian Counties, with grade I ecological tension index; ecological warning region, including Huxian, Chang'an, Lintong and Gaoling Counties, with grade II ecological tension index; and ecological insecurity region, including Xi'an Cantonal and Yanliang County, with grade III ecological tension index. After 1991, ecological security change shows three types of trend: Declining ecological tension index type, including Zhouzhi, Lantian, Gaoling and Huxian counties, with improving ecological environment; rising ecological tension index type, including Lintong and Chang'an Counties, with deteriorating ecological environment; and static ecological tension index type, including Xi'an Cantonal and Yanliang County. Onto 2003, the ecological state of Xi'an City can be divided into two strata: ecological safety region and ecological insecurity region. Zhouzhi and Lantian Counties still belong to ecological security region; Huxian and Gaoling Counties have moved up from ecological warning region to ecological security region; yet Chang'an and Lintong Counties have dropped down from ecological warning region to ecological insecurity region; while Xi’an Cantonal and Yanliang County still remain in ecological insecurity region.