Study On Urban Expansion And Its Effects On Eco-Environment In Xi'An Region Based On Landsat TM Data

In recent years, the research on Land Use/Cover Change (LUCC) and its effects on eco-environment has attracted more and more scientists to pay attention to it. However, the ecological effects induced by urban expansion were seldom covered. The objective of this paper is to retrieve the information of urban expansion (1988-2003) in Xi'an region and its effects on eco-environment by using Landsat TM satellite images.In this study, two TM images of the study area (1988 and 2003) were used. After imagery pre-processing, which included atmospheric correction, geometric correction, and orthographic correction, ratio residential-area index (RRI) was proposed to retrieve the urban information. RRI is an index like RVI (ratio vegetation index), which can reflect the information of residential area. Compared with maximum likelihood classification (MLC) and artificial neural network (ANN) classification, the retrieval method of RRI could eliminate the influence of barrens, thus the accuracy of RRI was also higher than that of MLC and ANN. By analyzing the urban area in 1988 and 2003, the urban expansion of Xi'an region during the 15 years was obtained. In addition, supervised classification was used to retrieve land use information. The training samples were selected according to spectrum features, and the TM images of Xi'an region in 1988 and 2003 were classified into 6 land use types respectively, namely woodland, farmland, orchard, urban areas, water-body and uncultivated. With the help of area transfer matrix of land use changes, the relationship between urban expansion and the other five land uses was also analyzed. This could tell us where the expansion came from. At last, using related statistics data and environment detection data that we collected, the effects of urban expansion on eco-environment were analyzed.Through this study, the conclusions were drew as follows:(1) By using RRI, the information of urban expansion in Xi'an from 1988 to 2003 was acquired. And the overall accuracy of RRI, MLC and ANN were 87.08%, 75.83% and 79.17%, respectively. During the 15 years, the urban area of Xi'an region increased 51.84% from 87.251 Km~2 in 1988 to 132.482 Km~2 in 2003.(2) The urban expansion area was mainly transferred from farmland, uncultivated land, orchard and water-body. And farmland did the most important contribution to urban expansion.(3) The eco-environmental effects of urban expansion in the study area were not very optimistic. The pollution of water resources, Heat Island Effect and geological hazards were the most 3 obvious problems. Because of urban expansion and economic development, water pollution had induced water supply shortage in Xi'an region; With the continual increase of urban area which changed the ground feature, the annual average temperature of Xi'an city has increased 1.8℃ from 1989 to 2001; Urban expansion also needed more water supplies, which resulted in overexploiting ground water that caused many geological problems like ground subsidence and split.