Response of ecological environment change to urban construction land expansion in Bole City of Xinjiang

Abstract: At present, China is in the rapid development stage of urbanization, while urbanization is exerting its positive effect, and it inevitably brings negative effects. The "urban social problems" in the form of urban ecological deterioration is becoming more and more concerned by the government and the society. Therefore, it is very important for timely, accurately and quickly detecting the ecological changes which caused by the urban expansion. Four evaluation indices, such as humidity (Wet), green degree (NDVI), dry degree (NDBI) and heat degree (LST) were extracted from Landsat remote sensing images (2000—2016), and the integrated index method was used to deal with the normalized environmental factors, and the final evaluation results of the ecological environment of Bole City were obtained. And the spatial expansion pattern of Bole City was analyzed by using the urban expansion intensity index and the gravity center displacement model. The results showed that the ecological environment quality of Bole City had deteriorated to some extent during 2000—2016. The remote sensing ecological index (RSEI)values of the Bole city decreased from 0.703 in 2000 to 0.688 in 2011 and 0.565 in 2016. The RSEI level of the ecosystem ranged from 81.78% in 2000 to 76.8% in 2011, and then to 64.15% in 2016. During 2000—2016, the area of improved ecological environment was 1 051.65 km2 (accounting for 13.50%), and the area of deteriorated ecological environment was 3 064.59 km2 (accounting for 39.34%). It indicated that the ecological environment of Bole City was deteriorating during 2000—2016, but some parts of the ecological environment was improved. Spatial analysis showed that, the areas where had healthy ecological environment were mainly distributed in the front of the mountain plain, the old city and its surrounding areas; the ecological environment poor region was mainly distributed in the outlying areas of the main urban area and along the banks of Bortala River. Further analysis showed that the built-up area had increased by 11.04 km2, showing a trend of gradual expansion. During the entire study period (2000—2016), gravity center of Bole City had shifted to different directions; During 2000—2011, the gravity center of the city was moved to the southeast direction (SE) by 2.13 km; During 2011—2016, the gravity center of the city was shifted to the Northeast (NE) direction about 5.17 km; The city expanded in a planar distribution during 2000—2016, the gravity center of the city moved to the east in a large scale, as well as showed small scale transformation to the north, south and westward in a planar distribution. The areas where were affected by urban expansion, characteristic of extension and RSEI results further indicated city expansion was a predominate factor of ecological environment deterioration in the study area. In a word, this paper used remote sensing ecological index to comprehensively evaluate the ecological changes of Bole with multi-index, large-scale and multi-phase, and discussed the response of ecological environment to the urban land expansion. On the one hand, it can serve the ecological environment monitoring and ecological city construction of Bole city; on the other hand, it can test the applicability and effectiveness of RSEI in arid areas.