Land use change with topographic gradients in the Yuci District rapid urbanization area

The influence of topographic factors on land use change is significant for land use and cover change research. In order to explore the characteristics of land use change with different topographic gradients, in this study, ASTER GDEM data and remote sensing data of Yuci District in 2000, 2008, and 2016 were used to analyze the spatio-temporal characteristics of land use change from 2000 to 2016. The distribution characteristics and varying development of each land use type with aspect gradient, slope change rate, landform relief, and terrain niche were analyzed. The results showed the following: 1) from 2000 to 2016, construction land expanded primarily to the northwest and was mainly distributed in areas with a landform relief less than 30 m, a slope change rate less than 2°, a sunny slope or semi-sunny slope, and a terrain niche grade area of 1-3. The land uses of Yuci District were mainly construction, crop land, and unused land, which accounted for more than 93% of the research area. The crop land area is the largest, accounting for an average 46.91% of total land area in 2000, 2008, and 2016. The land use change was characterized by a decrease in unused land area and an increase in crop and construction land areas. The construction land area increased by 43.07 km², while the unused land area decreased by 37.33 km² from 2000 to 2008. However, from 2008 to 2016, the unused land area decreased by 221.00 km², while the crop and construction land areas increased by 170.61 km² and 37.36 km², respectively. 2) Construction land, crop land, and water were mainly distributed on low gradients of landform relief, slope change rate, and terrain niche. Conversely, forest land and unused land were mainly distributed on middle and high gradients of the three topographic factors. The construction land and crop land was predominantly distributed on flat land, with sunny or semi-sunny slopes, while forest land was predominantly distributed along shady and semi-shady slopes. The distribution of unused land was predominantly along sunny and semi-sunny slopes. From 2000 to 2016, the main distribution area of crop land gradually expanded to areas with a landform relief greater than 30 m, a slope change rate of 2°-15°, and a terrain niche of 4-7 grade area. There were evident differences in the topographic gradient of land use change as a result of topographic factors, human activity, policy factors, transportation, and location. Therefore, this study provides a scientific basis for rational planning and utilization of land in the process of regional urbanization and decision support for ecological environment management.